ceph: capability management

The Ceph metadata servers control client access to inode metadata and
file data by issuing capabilities, granting clients permission to read
and/or write both inode field and file data to OSDs (storage nodes).
Each capability consists of a set of bits indicating which operations
are allowed.

If the client holds a *_SHARED cap, the client has a coherent value
that can be safely read from the cached inode.

In the case of a *_EXCL (exclusive) or FILE_WR capabilities, the client
is allowed to change inode attributes (e.g., file size, mtime), note
its dirty state in the ceph_cap, and asynchronously flush that
metadata change to the MDS.

In the event of a conflicting operation (perhaps by another client),
the MDS will revoke the conflicting client capabilities.

In order for a client to cache an inode, it must hold a capability
with at least one MDS server.  When inodes are released, release
notifications are batched and periodically sent en masse to the MDS
cluster to release server state.

Signed-off-by: Sage Weil <sage@newdream.net>

1 files changed, 2830 insertions, 0 deletions

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
new file mode 100644
index 0000000..5c7d0e9
--- /dev/null
+++ b/fs/ceph/caps.c
@@ -0,0 +1,2830 @@
+#include "ceph_debug.h"
+
+#include <linux/fs.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/vmalloc.h>
+#include <linux/wait.h>
+
+#include "super.h"
+#include "decode.h"
+#include "messenger.h"
+
+/*
+ * Capability management
+ *
+ * The Ceph metadata servers control client access to inode metadata
+ * and file data by issuing capabilities, granting clients permission
+ * to read and/or write both inode field and file data to OSDs
+ * (storage nodes).  Each capability consists of a set of bits
+ * indicating which operations are allowed.
+ *
+ * If the client holds a *_SHARED cap, the client has a coherent value
+ * that can be safely read from the cached inode.
+ *
+ * In the case of a *_EXCL (exclusive) or FILE_WR capabilities, the
+ * client is allowed to change inode attributes (e.g., file size,
+ * mtime), note its dirty state in the ceph_cap, and asynchronously
+ * flush that metadata change to the MDS.
+ *
+ * In the event of a conflicting operation (perhaps by another
+ * client), the MDS will revoke the conflicting client capabilities.
+ *
+ * In order for a client to cache an inode, it must hold a capability
+ * with at least one MDS server.  When inodes are released, release
+ * notifications are batched and periodically sent en masse to the MDS
+ * cluster to release server state.
+ */
+
+
+/*
+ * Generate readable cap strings for debugging output.
+ */
+#define MAX_CAP_STR 20
+static char cap_str[MAX_CAP_STR][40];
+static DEFINE_SPINLOCK(cap_str_lock);
+static int last_cap_str;
+
+static char *gcap_string(char *s, int c)
+{
+	if (c & CEPH_CAP_GSHARED)
+		*s++ = 's';
+	if (c & CEPH_CAP_GEXCL)
+		*s++ = 'x';
+	if (c & CEPH_CAP_GCACHE)
+		*s++ = 'c';
+	if (c & CEPH_CAP_GRD)
+		*s++ = 'r';
+	if (c & CEPH_CAP_GWR)
+		*s++ = 'w';
+	if (c & CEPH_CAP_GBUFFER)
+		*s++ = 'b';
+	if (c & CEPH_CAP_GLAZYIO)
+		*s++ = 'l';
+	return s;
+}
+
+const char *ceph_cap_string(int caps)
+{
+	int i;
+	char *s;
+	int c;
+
+	spin_lock(&cap_str_lock);
+	i = last_cap_str++;
+	if (last_cap_str == MAX_CAP_STR)
+		last_cap_str = 0;
+	spin_unlock(&cap_str_lock);
+
+	s = cap_str[i];
+
+	if (caps & CEPH_CAP_PIN)
+		*s++ = 'p';
+
+	c = (caps >> CEPH_CAP_SAUTH) & 3;
+	if (c) {
+		*s++ = 'A';
+		s = gcap_string(s, c);
+	}
+
+	c = (caps >> CEPH_CAP_SLINK) & 3;
+	if (c) {
+		*s++ = 'L';
+		s = gcap_string(s, c);
+	}
+
+	c = (caps >> CEPH_CAP_SXATTR) & 3;
+	if (c) {
+		*s++ = 'X';
+		s = gcap_string(s, c);
+	}
+
+	c = caps >> CEPH_CAP_SFILE;
+	if (c) {
+		*s++ = 'F';
+		s = gcap_string(s, c);
+	}
+
+	if (s == cap_str[i])
+		*s++ = '-';
+	*s = 0;
+	return cap_str[i];
+}
+
+/*
+ * Cap reservations
+ *
+ * Maintain a global pool of preallocated struct ceph_caps, referenced
+ * by struct ceph_caps_reservations.  This ensures that we preallocate
+ * memory needed to successfully process an MDS response.  (If an MDS
+ * sends us cap information and we fail to process it, we will have
+ * problems due to the client and MDS being out of sync.)
+ *
+ * Reservations are 'owned' by a ceph_cap_reservation context.
+ */
+static spinlock_t caps_list_lock;
+static struct list_head caps_list;  /* unused (reserved or unreserved) */
+static int caps_total_count;        /* total caps allocated */
+static int caps_use_count;          /* in use */
+static int caps_reserve_count;      /* unused, reserved */
+static int caps_avail_count;        /* unused, unreserved */
+
+void __init ceph_caps_init(void)
+{
+	INIT_LIST_HEAD(&caps_list);
+	spin_lock_init(&caps_list_lock);
+}
+
+void ceph_caps_finalize(void)
+{
+	struct ceph_cap *cap;
+
+	spin_lock(&caps_list_lock);
+	while (!list_empty(&caps_list)) {
+		cap = list_first_entry(&caps_list, struct ceph_cap, caps_item);
+		list_del(&cap->caps_item);
+		kmem_cache_free(ceph_cap_cachep, cap);
+	}
+	caps_total_count = 0;
+	caps_avail_count = 0;
+	caps_use_count = 0;
+	caps_reserve_count = 0;
+	spin_unlock(&caps_list_lock);
+}
+
+int ceph_reserve_caps(struct ceph_cap_reservation *ctx, int need)
+{
+	int i;
+	struct ceph_cap *cap;
+	int have;
+	int alloc = 0;
+	LIST_HEAD(newcaps);
+	int ret = 0;
+
+	dout("reserve caps ctx=%p need=%d\n", ctx, need);
+
+	/* first reserve any caps that are already allocated */
+	spin_lock(&caps_list_lock);
+	if (caps_avail_count >= need)
+		have = need;
+	else
+		have = caps_avail_count;
+	caps_avail_count -= have;
+	caps_reserve_count += have;
+	BUG_ON(caps_total_count != caps_use_count + caps_reserve_count +
+	       caps_avail_count);
+	spin_unlock(&caps_list_lock);
+
+	for (i = have; i < need; i++) {
+		cap = kmem_cache_alloc(ceph_cap_cachep, GFP_NOFS);
+		if (!cap) {
+			ret = -ENOMEM;
+			goto out_alloc_count;
+		}
+		list_add(&cap->caps_item, &newcaps);
+		alloc++;
+	}
+	BUG_ON(have + alloc != need);
+
+	spin_lock(&caps_list_lock);
+	caps_total_count += alloc;
+	caps_reserve_count += alloc;
+	list_splice(&newcaps, &caps_list);
+
+	BUG_ON(caps_total_count != caps_use_count + caps_reserve_count +
+	       caps_avail_count);
+	spin_unlock(&caps_list_lock);
+
+	ctx->count = need;
+	dout("reserve caps ctx=%p %d = %d used + %d resv + %d avail\n",
+	     ctx, caps_total_count, caps_use_count, caps_reserve_count,
+	     caps_avail_count);
+	return 0;
+
+out_alloc_count:
+	/* we didn't manage to reserve as much as we needed */
+	pr_warning("reserve caps ctx=%p ENOMEM need=%d got=%d\n",
+		   ctx, need, have);
+	return ret;
+}
+
+int ceph_unreserve_caps(struct ceph_cap_reservation *ctx)
+{
+	dout("unreserve caps ctx=%p count=%d\n", ctx, ctx->count);
+	if (ctx->count) {
+		spin_lock(&caps_list_lock);
+		BUG_ON(caps_reserve_count < ctx->count);
+		caps_reserve_count -= ctx->count;
+		caps_avail_count += ctx->count;
+		ctx->count = 0;
+		dout("unreserve caps %d = %d used + %d resv + %d avail\n",
+		     caps_total_count, caps_use_count, caps_reserve_count,
+		     caps_avail_count);
+		BUG_ON(caps_total_count != caps_use_count + caps_reserve_count +
+		       caps_avail_count);
+		spin_unlock(&caps_list_lock);
+	}
+	return 0;
+}
+
+static struct ceph_cap *get_cap(struct ceph_cap_reservation *ctx)
+{
+	struct ceph_cap *cap = NULL;
+
+	/* temporary, until we do something about cap import/export */
+	if (!ctx)
+		return kmem_cache_alloc(ceph_cap_cachep, GFP_NOFS);
+
+	spin_lock(&caps_list_lock);
+	dout("get_cap ctx=%p (%d) %d = %d used + %d resv + %d avail\n",
+	     ctx, ctx->count, caps_total_count, caps_use_count,
+	     caps_reserve_count, caps_avail_count);
+	BUG_ON(!ctx->count);
+	BUG_ON(ctx->count > caps_reserve_count);
+	BUG_ON(list_empty(&caps_list));
+
+	ctx->count--;
+	caps_reserve_count--;
+	caps_use_count++;
+
+	cap = list_first_entry(&caps_list, struct ceph_cap, caps_item);
+	list_del(&cap->caps_item);
+
+	BUG_ON(caps_total_count != caps_use_count + caps_reserve_count +
+	       caps_avail_count);
+	spin_unlock(&caps_list_lock);
+	return cap;
+}
+
+static void put_cap(struct ceph_cap *cap,
+		    struct ceph_cap_reservation *ctx)
+{
+	spin_lock(&caps_list_lock);
+	dout("put_cap ctx=%p (%d) %d = %d used + %d resv + %d avail\n",
+	     ctx, ctx ? ctx->count : 0, caps_total_count, caps_use_count,
+	     caps_reserve_count, caps_avail_count);
+	caps_use_count--;
+	/*
+	 * Keep some preallocated caps around, at least enough to do a
+	 * readdir (which needs to preallocate lots of them), to avoid
+	 * lots of free/alloc churn.
+	 */
+	if (caps_avail_count >= caps_reserve_count +
+	    ceph_client(cap->ci->vfs_inode.i_sb)->mount_args.max_readdir) {
+		caps_total_count--;
+		kmem_cache_free(ceph_cap_cachep, cap);
+	} else {
+		if (ctx) {
+			ctx->count++;
+			caps_reserve_count++;
+		} else {
+			caps_avail_count++;
+		}
+		list_add(&cap->caps_item, &caps_list);
+	}
+
+	BUG_ON(caps_total_count != caps_use_count + caps_reserve_count +
+	       caps_avail_count);
+	spin_unlock(&caps_list_lock);
+}
+
+void ceph_reservation_status(struct ceph_client *client,
+			     int *total, int *avail, int *used, int *reserved)
+{
+	if (total)
+		*total = caps_total_count;
+	if (avail)
+		*avail = caps_avail_count;
+	if (used)
+		*used = caps_use_count;
+	if (reserved)
+		*reserved = caps_reserve_count;
+}
+
+/*
+ * Find ceph_cap for given mds, if any.
+ *
+ * Called with i_lock held.
+ */
+static struct ceph_cap *__get_cap_for_mds(struct ceph_inode_info *ci, int mds)
+{
+	struct ceph_cap *cap;
+	struct rb_node *n = ci->i_caps.rb_node;
+
+	while (n) {
+		cap = rb_entry(n, struct ceph_cap, ci_node);
+		if (mds < cap->mds)
+			n = n->rb_left;
+		else if (mds > cap->mds)
+			n = n->rb_right;
+		else
+			return cap;
+	}
+	return NULL;
+}
+
+/*
+ * Return id of any MDS with a cap, preferably FILE_WR|WRBUFFER|EXCL, else
+ * -1.
+ */
+static int __ceph_get_cap_mds(struct ceph_inode_info *ci, u32 *mseq)
+{
+	struct ceph_cap *cap;
+	int mds = -1;
+	struct rb_node *p;
+
+	/* prefer mds with WR|WRBUFFER|EXCL caps */
+	for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
+		cap = rb_entry(p, struct ceph_cap, ci_node);
+		mds = cap->mds;
+		if (mseq)
+			*mseq = cap->mseq;
+		if (cap->issued & (CEPH_CAP_FILE_WR |
+				   CEPH_CAP_FILE_BUFFER |
+				   CEPH_CAP_FILE_EXCL))
+			break;
+	}
+	return mds;
+}
+
+int ceph_get_cap_mds(struct inode *inode)
+{
+	int mds;
+	spin_lock(&inode->i_lock);
+	mds = __ceph_get_cap_mds(ceph_inode(inode), NULL);
+	spin_unlock(&inode->i_lock);
+	return mds;
+}
+
+/*
+ * Called under i_lock.
+ */
+static void __insert_cap_node(struct ceph_inode_info *ci,
+			      struct ceph_cap *new)
+{
+	struct rb_node **p = &ci->i_caps.rb_node;
+	struct rb_node *parent = NULL;
+	struct ceph_cap *cap = NULL;
+
+	while (*p) {
+		parent = *p;
+		cap = rb_entry(parent, struct ceph_cap, ci_node);
+		if (new->mds < cap->mds)
+			p = &(*p)->rb_left;
+		else if (new->mds > cap->mds)
+			p = &(*p)->rb_right;
+		else
+			BUG();
+	}
+
+	rb_link_node(&new->ci_node, parent, p);
+	rb_insert_color(&new->ci_node, &ci->i_caps);
+}
+
+/*
+ * (re)set cap hold timeouts, which control the delayed release
+ * of unused caps back to the MDS.  Should be called on cap use.
+ */
+static void __cap_set_timeouts(struct ceph_mds_client *mdsc,
+			       struct ceph_inode_info *ci)
+{
+	struct ceph_mount_args *ma = &mdsc->client->mount_args;
+
+	ci->i_hold_caps_min = round_jiffies(jiffies +
+					    ma->caps_wanted_delay_min * HZ);
+	ci->i_hold_caps_max = round_jiffies(jiffies +
+					    ma->caps_wanted_delay_max * HZ);
+	dout("__cap_set_timeouts %p min %lu max %lu\n", &ci->vfs_inode,
+	     ci->i_hold_caps_min - jiffies, ci->i_hold_caps_max - jiffies);
+}
+
+/*
+ * (Re)queue cap at the end of the delayed cap release list.
+ *
+ * If I_FLUSH is set, leave the inode at the front of the list.
+ *
+ * Caller holds i_lock
+ *    -> we take mdsc->cap_delay_lock
+ */
+static void __cap_delay_requeue(struct ceph_mds_client *mdsc,
+				struct ceph_inode_info *ci)
+{
+	__cap_set_timeouts(mdsc, ci);
+	dout("__cap_delay_requeue %p flags %d at %lu\n", &ci->vfs_inode,
+	     ci->i_ceph_flags, ci->i_hold_caps_max);
+	if (!mdsc->stopping) {
+		spin_lock(&mdsc->cap_delay_lock);
+		if (!list_empty(&ci->i_cap_delay_list)) {
+			if (ci->i_ceph_flags & CEPH_I_FLUSH)
+				goto no_change;
+			list_del_init(&ci->i_cap_delay_list);
+		}
+		list_add_tail(&ci->i_cap_delay_list, &mdsc->cap_delay_list);
+no_change:
+		spin_unlock(&mdsc->cap_delay_lock);
+	}
+}
+
+/*
+ * Queue an inode for immediate writeback.  Mark inode with I_FLUSH,
+ * indicating we should send a cap message to flush dirty metadata
+ * asap, and move to the front of the delayed cap list.
+ */
+static void __cap_delay_requeue_front(struct ceph_mds_client *mdsc,
+				      struct ceph_inode_info *ci)
+{
+	dout("__cap_delay_requeue_front %p\n", &ci->vfs_inode);
+	spin_lock(&mdsc->cap_delay_lock);
+	ci->i_ceph_flags |= CEPH_I_FLUSH;
+	if (!list_empty(&ci->i_cap_delay_list))
+		list_del_init(&ci->i_cap_delay_list);
+	list_add(&ci->i_cap_delay_list, &mdsc->cap_delay_list);
+	spin_unlock(&mdsc->cap_delay_lock);
+}
+
+/*
+ * Cancel delayed work on cap.
+ *
+ * Caller must hold i_lock.
+ */
+static void __cap_delay_cancel(struct ceph_mds_client *mdsc,
+			       struct ceph_inode_info *ci)
+{
+	dout("__cap_delay_cancel %p\n", &ci->vfs_inode);
+	if (list_empty(&ci->i_cap_delay_list))
+		return;
+	spin_lock(&mdsc->cap_delay_lock);
+	list_del_init(&ci->i_cap_delay_list);
+	spin_unlock(&mdsc->cap_delay_lock);
+}
+
+/*
+ * Common issue checks for add_cap, handle_cap_grant.
+ */
+static void __check_cap_issue(struct ceph_inode_info *ci, struct ceph_cap *cap,
+			      unsigned issued)
+{
+	unsigned had = __ceph_caps_issued(ci, NULL);
+
+	/*
+	 * Each time we receive FILE_CACHE anew, we increment
+	 * i_rdcache_gen.
+	 */
+	if ((issued & CEPH_CAP_FILE_CACHE) &&
+	    (had & CEPH_CAP_FILE_CACHE) == 0)
+		ci->i_rdcache_gen++;
+
+	/*
+	 * if we are newly issued FILE_SHARED, clear I_COMPLETE; we
+	 * don't know what happened to this directory while we didn't
+	 * have the cap.
+	 */
+	if ((issued & CEPH_CAP_FILE_SHARED) &&
+	    (had & CEPH_CAP_FILE_SHARED) == 0) {
+		ci->i_shared_gen++;
+		if (S_ISDIR(ci->vfs_inode.i_mode)) {
+			dout(" marking %p NOT complete\n", &ci->vfs_inode);
+			ci->i_ceph_flags &= ~CEPH_I_COMPLETE;
+		}
+	}
+}
+
+/*
+ * Add a capability under the given MDS session.
+ *
+ * Caller should hold session snap_rwsem (read) and s_mutex.
+ *
+ * @fmode is the open file mode, if we are opening a file, otherwise
+ * it is < 0.  (This is so we can atomically add the cap and add an
+ * open file reference to it.)
+ */
+int ceph_add_cap(struct inode *inode,
+		 struct ceph_mds_session *session, u64 cap_id,
+		 int fmode, unsigned issued, unsigned wanted,
+		 unsigned seq, unsigned mseq, u64 realmino, int flags,
+		 struct ceph_cap_reservation *caps_reservation)
+{
+	struct ceph_mds_client *mdsc = &ceph_inode_to_client(inode)->mdsc;
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	struct ceph_cap *new_cap = NULL;
+	struct ceph_cap *cap;
+	int mds = session->s_mds;
+	int actual_wanted;
+
+	dout("add_cap %p mds%d cap %llx %s seq %d\n", inode,
+	     session->s_mds, cap_id, ceph_cap_string(issued), seq);
+
+	/*
+	 * If we are opening the file, include file mode wanted bits
+	 * in wanted.
+	 */
+	if (fmode >= 0)
+		wanted |= ceph_caps_for_mode(fmode);
+
+retry:
+	spin_lock(&inode->i_lock);
+	cap = __get_cap_for_mds(ci, mds);
+	if (!cap) {
+		if (new_cap) {
+			cap = new_cap;
+			new_cap = NULL;
+		} else {
+			spin_unlock(&inode->i_lock);
+			new_cap = get_cap(caps_reservation);
+			if (new_cap == NULL)
+				return -ENOMEM;
+			goto retry;
+		}
+
+		cap->issued = 0;
+		cap->implemented = 0;
+		cap->mds = mds;
+		cap->mds_wanted = 0;
+
+		cap->ci = ci;
+		__insert_cap_node(ci, cap);
+
+		/* clear out old exporting info?  (i.e. on cap import) */
+		if (ci->i_cap_exporting_mds == mds) {
+			ci->i_cap_exporting_issued = 0;
+			ci->i_cap_exporting_mseq = 0;
+			ci->i_cap_exporting_mds = -1;
+		}
+
+		/* add to session cap list */
+		cap->session = session;
+		spin_lock(&session->s_cap_lock);
+		list_add_tail(&cap->session_caps, &session->s_caps);
+		session->s_nr_caps++;
+		spin_unlock(&session->s_cap_lock);
+	}
+
+	if (!ci->i_snap_realm) {
+		/*
+		 * add this inode to the appropriate snap realm
+		 */
+		struct ceph_snap_realm *realm = ceph_lookup_snap_realm(mdsc,
+							       realmino);
+		if (realm) {
+			ceph_get_snap_realm(mdsc, realm);
+			spin_lock(&realm->inodes_with_caps_lock);
+			ci->i_snap_realm = realm;
+			list_add(&ci->i_snap_realm_item,
+				 &realm->inodes_with_caps);
+			spin_unlock(&realm->inodes_with_caps_lock);
+		} else {
+			pr_err("ceph_add_cap: couldn't find snap realm %llx\n",
+			       realmino);
+		}
+	}
+
+	__check_cap_issue(ci, cap, issued);
+
+	/*
+	 * If we are issued caps we don't want, or the mds' wanted
+	 * value appears to be off, queue a check so we'll release
+	 * later and/or update the mds wanted value.
+	 */
+	actual_wanted = __ceph_caps_wanted(ci);
+	if ((wanted & ~actual_wanted) ||
+	    (issued & ~actual_wanted & CEPH_CAP_ANY_WR)) {
+		dout(" issued %s, mds wanted %s, actual %s, queueing\n",
+		     ceph_cap_string(issued), ceph_cap_string(wanted),
+		     ceph_cap_string(actual_wanted));
+		__cap_delay_requeue(mdsc, ci);
+	}
+
+	if (flags & CEPH_CAP_FLAG_AUTH)
+		ci->i_auth_cap = cap;
+	else if (ci->i_auth_cap == cap)
+		ci->i_auth_cap = NULL;
+
+	dout("add_cap inode %p (%llx.%llx) cap %p %s now %s seq %d mds%d\n",
+	     inode, ceph_vinop(inode), cap, ceph_cap_string(issued),
+	     ceph_cap_string(issued|cap->issued), seq, mds);
+	cap->cap_id = cap_id;
+	cap->issued = issued;
+	cap->implemented |= issued;
+	cap->mds_wanted |= wanted;
+	cap->seq = seq;
+	cap->issue_seq = seq;
+	cap->mseq = mseq;
+	cap->gen = session->s_cap_gen;
+
+	if (fmode >= 0)
+		__ceph_get_fmode(ci, fmode);
+	spin_unlock(&inode->i_lock);
+	wake_up(&ci->i_cap_wq);
+	return 0;
+}
+
+/*
+ * Return true if cap has not timed out and belongs to the current
+ * generation of the MDS session (i.e. has not gone 'stale' due to
+ * us losing touch with the mds).
+ */
+static int __cap_is_valid(struct ceph_cap *cap)
+{
+	unsigned long ttl;
+	u32 gen;
+
+	spin_lock(&cap->session->s_cap_lock);
+	gen = cap->session->s_cap_gen;
+	ttl = cap->session->s_cap_ttl;
+	spin_unlock(&cap->session->s_cap_lock);
+
+	if (cap->gen < gen || time_after_eq(jiffies, ttl)) {
+		dout("__cap_is_valid %p cap %p issued %s "
+		     "but STALE (gen %u vs %u)\n", &cap->ci->vfs_inode,
+		     cap, ceph_cap_string(cap->issued), cap->gen, gen);
+		return 0;
+	}
+
+	return 1;
+}
+
+/*
+ * Return set of valid cap bits issued to us.  Note that caps time
+ * out, and may be invalidated in bulk if the client session times out
+ * and session->s_cap_gen is bumped.
+ */
+int __ceph_caps_issued(struct ceph_inode_info *ci, int *implemented)
+{
+	int have = ci->i_snap_caps;
+	struct ceph_cap *cap;
+	struct rb_node *p;
+
+	if (implemented)
+		*implemented = 0;
+	for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
+		cap = rb_entry(p, struct ceph_cap, ci_node);
+		if (!__cap_is_valid(cap))
+			continue;
+		dout("__ceph_caps_issued %p cap %p issued %s\n",
+		     &ci->vfs_inode, cap, ceph_cap_string(cap->issued));
+		have |= cap->issued;
+		if (implemented)
+			*implemented |= cap->implemented;
+	}
+	return have;
+}
+
+/*
+ * Get cap bits issued by caps other than @ocap
+ */
+int __ceph_caps_issued_other(struct ceph_inode_info *ci, struct ceph_cap *ocap)
+{
+	int have = ci->i_snap_caps;
+	struct ceph_cap *cap;
+	struct rb_node *p;
+
+	for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
+		cap = rb_entry(p, struct ceph_cap, ci_node);
+		if (cap == ocap)
+			continue;
+		if (!__cap_is_valid(cap))
+			continue;
+		have |= cap->issued;
+	}
+	return have;
+}
+
+/*
+ * Move a cap to the end of the LRU (oldest caps at list head, newest
+ * at list tail).
+ */
+static void __touch_cap(struct ceph_cap *cap)
+{
+	struct ceph_mds_session *s = cap->session;
+
+	dout("__touch_cap %p cap %p mds%d\n", &cap->ci->vfs_inode, cap,
+	     s->s_mds);
+	spin_lock(&s->s_cap_lock);
+	list_move_tail(&cap->session_caps, &s->s_caps);
+	spin_unlock(&s->s_cap_lock);
+}
+
+/*
+ * Check if we hold the given mask.  If so, move the cap(s) to the
+ * front of their respective LRUs.  (This is the preferred way for
+ * callers to check for caps they want.)
+ */
+int __ceph_caps_issued_mask(struct ceph_inode_info *ci, int mask, int touch)
+{
+	struct ceph_cap *cap;
+	struct rb_node *p;
+	int have = ci->i_snap_caps;
+
+	if ((have & mask) == mask) {
+		dout("__ceph_caps_issued_mask %p snap issued %s"
+		     " (mask %s)\n", &ci->vfs_inode,
+		     ceph_cap_string(have),
+		     ceph_cap_string(mask));
+		return 1;
+	}
+
+	for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
+		cap = rb_entry(p, struct ceph_cap, ci_node);
+		if (!__cap_is_valid(cap))
+			continue;
+		if ((cap->issued & mask) == mask) {
+			dout("__ceph_caps_issued_mask %p cap %p issued %s"
+			     " (mask %s)\n", &ci->vfs_inode, cap,
+			     ceph_cap_string(cap->issued),
+			     ceph_cap_string(mask));
+			if (touch)
+				__touch_cap(cap);
+			return 1;
+		}
+
+		/* does a combination of caps satisfy mask? */
+		have |= cap->issued;
+		if ((have & mask) == mask) {
+			dout("__ceph_caps_issued_mask %p combo issued %s"
+			     " (mask %s)\n", &ci->vfs_inode,
+			     ceph_cap_string(cap->issued),
+			     ceph_cap_string(mask));
+			if (touch) {
+				struct rb_node *q;
+
+				/* touch this + preceeding caps */
+				__touch_cap(cap);
+				for (q = rb_first(&ci->i_caps); q != p;
+				     q = rb_next(q)) {
+					cap = rb_entry(q, struct ceph_cap,
+						       ci_node);
+					if (!__cap_is_valid(cap))
+						continue;
+					__touch_cap(cap);
+				}
+			}
+			return 1;
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Return true if mask caps are currently being revoked by an MDS.
+ */
+int ceph_caps_revoking(struct ceph_inode_info *ci, int mask)
+{
+	struct inode *inode = &ci->vfs_inode;
+	struct ceph_cap *cap;
+	struct rb_node *p;
+	int ret = 0;
+
+	spin_lock(&inode->i_lock);
+	for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
+		cap = rb_entry(p, struct ceph_cap, ci_node);
+		if (__cap_is_valid(cap) &&
+		    (cap->implemented & ~cap->issued & mask)) {
+			ret = 1;
+			break;
+		}
+	}
+	spin_unlock(&inode->i_lock);
+	dout("ceph_caps_revoking %p %s = %d\n", inode,
+	     ceph_cap_string(mask), ret);
+	return ret;
+}
+
+int __ceph_caps_used(struct ceph_inode_info *ci)
+{
+	int used = 0;
+	if (ci->i_pin_ref)
+		used |= CEPH_CAP_PIN;
+	if (ci->i_rd_ref)
+		used |= CEPH_CAP_FILE_RD;
+	if (ci->i_rdcache_ref || ci->i_rdcache_gen)
+		used |= CEPH_CAP_FILE_CACHE;
+	if (ci->i_wr_ref)
+		used |= CEPH_CAP_FILE_WR;
+	if (ci->i_wrbuffer_ref)
+		used |= CEPH_CAP_FILE_BUFFER;
+	return used;
+}
+
+/*
+ * wanted, by virtue of open file modes
+ */
+int __ceph_caps_file_wanted(struct ceph_inode_info *ci)
+{
+	int want = 0;
+	int mode;
+	for (mode = 0; mode < 4; mode++)
+		if (ci->i_nr_by_mode[mode])
+			want |= ceph_caps_for_mode(mode);
+	return want;
+}
+
+/*
+ * Return caps we have registered with the MDS(s) as 'wanted'.
+ */
+int __ceph_caps_mds_wanted(struct ceph_inode_info *ci)
+{
+	struct ceph_cap *cap;
+	struct rb_node *p;
+	int mds_wanted = 0;
+
+	for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
+		cap = rb_entry(p, struct ceph_cap, ci_node);
+		if (!__cap_is_valid(cap))
+			continue;
+		mds_wanted |= cap->mds_wanted;
+	}
+	return mds_wanted;
+}
+
+/*
+ * called under i_lock
+ */
+static int __ceph_is_any_caps(struct ceph_inode_info *ci)
+{
+	return !RB_EMPTY_ROOT(&ci->i_caps) || ci->i_cap_exporting_mds >= 0;
+}
+
+/*
+ * caller should hold i_lock, and session s_mutex.
+ * returns true if this is the last cap.  if so, caller should iput.
+ */
+void __ceph_remove_cap(struct ceph_cap *cap,
+		       struct ceph_cap_reservation *ctx)
+{
+	struct ceph_mds_session *session = cap->session;
+	struct ceph_inode_info *ci = cap->ci;
+	struct ceph_mds_client *mdsc = &ceph_client(ci->vfs_inode.i_sb)->mdsc;
+
+	dout("__ceph_remove_cap %p from %p\n", cap, &ci->vfs_inode);
+
+	/* remove from session list */
+	spin_lock(&session->s_cap_lock);
+	list_del_init(&cap->session_caps);
+	session->s_nr_caps--;
+	spin_unlock(&session->s_cap_lock);
+
+	/* remove from inode list */
+	rb_erase(&cap->ci_node, &ci->i_caps);
+	cap->session = NULL;
+	if (ci->i_auth_cap == cap)
+		ci->i_auth_cap = NULL;
+
+	put_cap(cap, ctx);
+
+	if (!__ceph_is_any_caps(ci) && ci->i_snap_realm) {
+		struct ceph_snap_realm *realm = ci->i_snap_realm;
+		spin_lock(&realm->inodes_with_caps_lock);
+		list_del_init(&ci->i_snap_realm_item);
+		ci->i_snap_realm_counter++;
+		ci->i_snap_realm = NULL;
+		spin_unlock(&realm->inodes_with_caps_lock);
+		ceph_put_snap_realm(mdsc, realm);
+	}
+	if (!__ceph_is_any_real_caps(ci))
+		__cap_delay_cancel(mdsc, ci);
+}
+
+/*
+ * Build and send a cap message to the given MDS.
+ *
+ * Caller should be holding s_mutex.
+ */
+static int send_cap_msg(struct ceph_mds_session *session,
+			u64 ino, u64 cid, int op,
+			int caps, int wanted, int dirty,
+			u32 seq, u64 flush_tid, u32 issue_seq, u32 mseq,
+			u64 size, u64 max_size,
+			struct timespec *mtime, struct timespec *atime,
+			u64 time_warp_seq,
+			uid_t uid, gid_t gid, mode_t mode,
+			u64 xattr_version,
+			struct ceph_buffer *xattrs_buf,
+			u64 follows)
+{
+	struct ceph_mds_caps *fc;
+	struct ceph_msg *msg;
+
+	dout("send_cap_msg %s %llx %llx caps %s wanted %s dirty %s"
+	     " seq %u/%u mseq %u follows %lld size %llu/%llu"
+	     " xattr_ver %llu xattr_len %d\n", ceph_cap_op_name(op),
+	     cid, ino, ceph_cap_string(caps), ceph_cap_string(wanted),
+	     ceph_cap_string(dirty),
+	     seq, issue_seq, mseq, follows, size, max_size,
+	     xattr_version, xattrs_buf ? (int)xattrs_buf->vec.iov_len : 0);
+
+	msg = ceph_msg_new(CEPH_MSG_CLIENT_CAPS, sizeof(*fc), 0, 0, NULL);
+	if (IS_ERR(msg))
+		return PTR_ERR(msg);
+
+	fc = msg->front.iov_base;
+
+	memset(fc, 0, sizeof(*fc));
+
+	fc->cap_id = cpu_to_le64(cid);
+	fc->op = cpu_to_le32(op);
+	fc->seq = cpu_to_le32(seq);
+	fc->client_tid = cpu_to_le64(flush_tid);
+	fc->issue_seq = cpu_to_le32(issue_seq);
+	fc->migrate_seq = cpu_to_le32(mseq);
+	fc->caps = cpu_to_le32(caps);
+	fc->wanted = cpu_to_le32(wanted);
+	fc->dirty = cpu_to_le32(dirty);
+	fc->ino = cpu_to_le64(ino);
+	fc->snap_follows = cpu_to_le64(follows);
+
+	fc->size = cpu_to_le64(size);
+	fc->max_size = cpu_to_le64(max_size);
+	if (mtime)
+		ceph_encode_timespec(&fc->mtime, mtime);
+	if (atime)
+		ceph_encode_timespec(&fc->atime, atime);
+	fc->time_warp_seq = cpu_to_le32(time_warp_seq);
+
+	fc->uid = cpu_to_le32(uid);
+	fc->gid = cpu_to_le32(gid);
+	fc->mode = cpu_to_le32(mode);
+
+	fc->xattr_version = cpu_to_le64(xattr_version);
+	if (xattrs_buf) {
+		msg->middle = ceph_buffer_get(xattrs_buf);
+		fc->xattr_len = cpu_to_le32(xattrs_buf->vec.iov_len);
+		msg->hdr.middle_len = cpu_to_le32(xattrs_buf->vec.iov_len);
+	}
+
+	ceph_con_send(&session->s_con, msg);
+	return 0;
+}
+
+/*
+ * Queue cap releases when an inode is dropped from our
+ * cache.
+ */
+void ceph_queue_caps_release(struct inode *inode)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	struct rb_node *p;
+
+	spin_lock(&inode->i_lock);
+	p = rb_first(&ci->i_caps);
+	while (p) {
+		struct ceph_cap *cap = rb_entry(p, struct ceph_cap, ci_node);
+		struct ceph_mds_session *session = cap->session;
+		struct ceph_msg *msg;
+		struct ceph_mds_cap_release *head;
+		struct ceph_mds_cap_item *item;
+
+		spin_lock(&session->s_cap_lock);
+		BUG_ON(!session->s_num_cap_releases);
+		msg = list_first_entry(&session->s_cap_releases,
+				       struct ceph_msg, list_head);
+
+		dout(" adding %p release to mds%d msg %p (%d left)\n",
+		     inode, session->s_mds, msg, session->s_num_cap_releases);
+
+		BUG_ON(msg->front.iov_len + sizeof(*item) > PAGE_CACHE_SIZE);
+		head = msg->front.iov_base;
+		head->num = cpu_to_le32(le32_to_cpu(head->num) + 1);
+		item = msg->front.iov_base + msg->front.iov_len;
+		item->ino = cpu_to_le64(ceph_ino(inode));
+		item->cap_id = cpu_to_le64(cap->cap_id);
+		item->migrate_seq = cpu_to_le32(cap->mseq);
+		item->seq = cpu_to_le32(cap->issue_seq);
+
+		session->s_num_cap_releases--;
+
+		msg->front.iov_len += sizeof(*item);
+		if (le32_to_cpu(head->num) == CEPH_CAPS_PER_RELEASE) {
+			dout(" release msg %p full\n", msg);
+			list_move_tail(&msg->list_head,
+				      &session->s_cap_releases_done);
+		} else {
+			dout(" release msg %p at %d/%d (%d)\n", msg,
+			     (int)le32_to_cpu(head->num),
+			     (int)CEPH_CAPS_PER_RELEASE,
+			     (int)msg->front.iov_len);
+		}
+		spin_unlock(&session->s_cap_lock);
+		p = rb_next(p);
+		__ceph_remove_cap(cap, NULL);
+
+	}
+	spin_unlock(&inode->i_lock);
+}
+
+/*
+ * Send a cap msg on the given inode.  Update our caps state, then
+ * drop i_lock and send the message.
+ *
+ * Make note of max_size reported/requested from mds, revoked caps
+ * that have now been implemented.
+ *
+ * Make half-hearted attempt ot to invalidate page cache if we are
+ * dropping RDCACHE.  Note that this will leave behind locked pages
+ * that we'll then need to deal with elsewhere.
+ *
+ * Return non-zero if delayed release, or we experienced an error
+ * such that the caller should requeue + retry later.
+ *
+ * called with i_lock, then drops it.
+ * caller should hold snap_rwsem (read), s_mutex.
+ */
+static int __send_cap(struct ceph_mds_client *mdsc, struct ceph_cap *cap,
+		      int op, int used, int want, int retain, int flushing,
+		      unsigned *pflush_tid)
+	__releases(cap->ci->vfs_inode->i_lock)
+{
+	struct ceph_inode_info *ci = cap->ci;
+	struct inode *inode = &ci->vfs_inode;
+	u64 cap_id = cap->cap_id;
+	int held = cap->issued | cap->implemented;
+	int revoking = cap->implemented & ~cap->issued;
+	int dropping = cap->issued & ~retain;
+	int keep;
+	u64 seq, issue_seq, mseq, time_warp_seq, follows;
+	u64 size, max_size;
+	struct timespec mtime, atime;
+	int wake = 0;
+	mode_t mode;
+	uid_t uid;
+	gid_t gid;
+	struct ceph_mds_session *session;
+	u64 xattr_version = 0;
+	int delayed = 0;
+	u64 flush_tid = 0;
+	int i;
+	int ret;
+
+	dout("__send_cap %p cap %p session %p %s -> %s (revoking %s)\n",
+	     inode, cap, cap->session,
+	     ceph_cap_string(held), ceph_cap_string(held & retain),
+	     ceph_cap_string(revoking));
+	BUG_ON((retain & CEPH_CAP_PIN) == 0);
+
+	session = cap->session;
+
+	/* don't release wanted unless we've waited a bit. */
+	if ((ci->i_ceph_flags & CEPH_I_NODELAY) == 0 &&
+	    time_before(jiffies, ci->i_hold_caps_min)) {
+		dout(" delaying issued %s -> %s, wanted %s -> %s on send\n",
+		     ceph_cap_string(cap->issued),
+		     ceph_cap_string(cap->issued & retain),
+		     ceph_cap_string(cap->mds_wanted),
+		     ceph_cap_string(want));
+		want |= cap->mds_wanted;
+		retain |= cap->issued;
+		delayed = 1;
+	}
+	ci->i_ceph_flags &= ~(CEPH_I_NODELAY | CEPH_I_FLUSH);
+
+	cap->issued &= retain;  /* drop bits we don't want */
+	if (cap->implemented & ~cap->issued) {
+		/*
+		 * Wake up any waiters on wanted -> needed transition.
+		 * This is due to the weird transition from buffered
+		 * to sync IO... we need to flush dirty pages _before_
+		 * allowing sync writes to avoid reordering.
+		 */
+		wake = 1;
+	}
+	cap->implemented &= cap->issued | used;
+	cap->mds_wanted = want;
+
+	if (flushing) {
+		/*
+		 * assign a tid for flush operations so we can avoid
+		 * flush1 -> dirty1 -> flush2 -> flushack1 -> mark
+		 * clean type races.  track latest tid for every bit
+		 * so we can handle flush AxFw, flush Fw, and have the
+		 * first ack clean Ax.
+		 */
+		flush_tid = ++ci->i_cap_flush_last_tid;
+		if (pflush_tid)
+			*pflush_tid = flush_tid;
+		dout(" cap_flush_tid %d\n", (int)flush_tid);
+		for (i = 0; i < CEPH_CAP_BITS; i++)
+			if (flushing & (1 << i))
+				ci->i_cap_flush_tid[i] = flush_tid;
+	}
+
+	keep = cap->implemented;
+	seq = cap->seq;
+	issue_seq = cap->issue_seq;
+	mseq = cap->mseq;
+	size = inode->i_size;
+	ci->i_reported_size = size;
+	max_size = ci->i_wanted_max_size;
+	ci->i_requested_max_size = max_size;
+	mtime = inode->i_mtime;
+	atime = inode->i_atime;
+	time_warp_seq = ci->i_time_warp_seq;
+	follows = ci->i_snap_realm->cached_context->seq;
+	uid = inode->i_uid;
+	gid = inode->i_gid;
+	mode = inode->i_mode;
+
+	if (dropping & CEPH_CAP_XATTR_EXCL) {
+		__ceph_build_xattrs_blob(ci);
+		xattr_version = ci->i_xattrs.version + 1;
+	}
+
+	spin_unlock(&inode->i_lock);
+
+	if (dropping & CEPH_CAP_FILE_CACHE) {
+		/* invalidate what we can */
+		dout("invalidating pages on %p\n", inode);
+		invalidate_mapping_pages(&inode->i_data, 0, -1);
+	}
+
+	ret = send_cap_msg(session, ceph_vino(inode).ino, cap_id,
+		op, keep, want, flushing, seq, flush_tid, issue_seq, mseq,
+		size, max_size, &mtime, &atime, time_warp_seq,
+		uid, gid, mode,
+		xattr_version,
+		(flushing & CEPH_CAP_XATTR_EXCL) ? ci->i_xattrs.blob : NULL,
+		follows);
+	if (ret < 0) {
+		dout("error sending cap msg, must requeue %p\n", inode);
+		delayed = 1;
+	}
+
+	if (wake)
+		wake_up(&ci->i_cap_wq);
+
+	return delayed;
+}
+
+/*
+ * When a snapshot is taken, clients accumulate dirty metadata on
+ * inodes with capabilities in ceph_cap_snaps to describe the file
+ * state at the time the snapshot was taken.  This must be flushed
+ * asynchronously back to the MDS once sync writes complete and dirty
+ * data is written out.
+ *
+ * Called under i_lock.  Takes s_mutex as needed.
+ */
+void __ceph_flush_snaps(struct ceph_inode_info *ci,
+			struct ceph_mds_session **psession)
+{
+	struct inode *inode = &ci->vfs_inode;
+	int mds;
+	struct ceph_cap_snap *capsnap;
+	u32 mseq;
+	struct ceph_mds_client *mdsc = &ceph_inode_to_client(inode)->mdsc;
+	struct ceph_mds_session *session = NULL; /* if session != NULL, we hold
+						    session->s_mutex */
+	u64 next_follows = 0;  /* keep track of how far we've gotten through the
+			     i_cap_snaps list, and skip these entries next time
+			     around to avoid an infinite loop */
+
+	if (psession)
+		session = *psession;
+
+	dout("__flush_snaps %p\n", inode);
+retry:
+	list_for_each_entry(capsnap, &ci->i_cap_snaps, ci_item) {
+		/* avoid an infiniute loop after retry */
+		if (capsnap->follows < next_follows)
+			continue;
+		/*
+		 * we need to wait for sync writes to complete and for dirty
+		 * pages to be written out.
+		 */
+		if (capsnap->dirty_pages || capsnap->writing)
+			continue;
+
+		/* pick mds, take s_mutex */
+		mds = __ceph_get_cap_mds(ci, &mseq);
+		if (session && session->s_mds != mds) {
+			dout("oops, wrong session %p mutex\n", session);
+			mutex_unlock(&session->s_mutex);
+			ceph_put_mds_session(session);
+			session = NULL;
+		}
+		if (!session) {
+			spin_unlock(&inode->i_lock);
+			mutex_lock(&mdsc->mutex);
+			session = __ceph_lookup_mds_session(mdsc, mds);
+			mutex_unlock(&mdsc->mutex);
+			if (session) {
+				dout("inverting session/ino locks on %p\n",
+				     session);
+				mutex_lock(&session->s_mutex);
+			}
+			/*
+			 * if session == NULL, we raced against a cap
+			 * deletion.  retry, and we'll get a better
+			 * @mds value next time.
+			 */
+			spin_lock(&inode->i_lock);
+			goto retry;
+		}
+
+		capsnap->flush_tid = ++ci->i_cap_flush_last_tid;
+		atomic_inc(&capsnap->nref);
+		if (!list_empty(&capsnap->flushing_item))
+			list_del_init(&capsnap->flushing_item);
+		list_add_tail(&capsnap->flushing_item,
+			      &session->s_cap_snaps_flushing);
+		spin_unlock(&inode->i_lock);
+
+		dout("flush_snaps %p cap_snap %p follows %lld size %llu\n",
+		     inode, capsnap, next_follows, capsnap->size);
+		send_cap_msg(session, ceph_vino(inode).ino, 0,
+			     CEPH_CAP_OP_FLUSHSNAP, capsnap->issued, 0,
+			     capsnap->dirty, 0, capsnap->flush_tid, 0, mseq,
+			     capsnap->size, 0,
+			     &capsnap->mtime, &capsnap->atime,
+			     capsnap->time_warp_seq,
+			     capsnap->uid, capsnap->gid, capsnap->mode,
+			     0, NULL,
+			     capsnap->follows);
+
+		next_follows = capsnap->follows + 1;
+		ceph_put_cap_snap(capsnap);
+
+		spin_lock(&inode->i_lock);
+		goto retry;
+	}
+
+	/* we flushed them all; remove this inode from the queue */
+	spin_lock(&mdsc->snap_flush_lock);
+	list_del_init(&ci->i_snap_flush_item);
+	spin_unlock(&mdsc->snap_flush_lock);
+
+	if (psession)
+		*psession = session;
+	else if (session) {
+		mutex_unlock(&session->s_mutex);
+		ceph_put_mds_session(session);
+	}
+}
+
+static void ceph_flush_snaps(struct ceph_inode_info *ci)
+{
+	struct inode *inode = &ci->vfs_inode;
+
+	spin_lock(&inode->i_lock);
+	__ceph_flush_snaps(ci, NULL);
+	spin_unlock(&inode->i_lock);
+}
+
+/*
+ * Add dirty inode to the flushing list.  Assigned a seq number so we
+ * can wait for caps to flush without starving.
+ */
+static void __mark_caps_flushing(struct inode *inode,
+				 struct ceph_mds_session *session)
+{
+	struct ceph_mds_client *mdsc = &ceph_client(inode->i_sb)->mdsc;
+	struct ceph_inode_info *ci = ceph_inode(inode);
+
+	BUG_ON(list_empty(&ci->i_dirty_item));
+	spin_lock(&mdsc->cap_dirty_lock);
+	if (list_empty(&ci->i_flushing_item)) {
+		list_add_tail(&ci->i_flushing_item, &session->s_cap_flushing);
+		mdsc->num_cap_flushing++;
+		ci->i_cap_flush_seq = ++mdsc->cap_flush_seq;
+		dout(" inode %p now flushing seq %lld\n", &ci->vfs_inode,
+		     ci->i_cap_flush_seq);
+	}
+	spin_unlock(&mdsc->cap_dirty_lock);
+}
+
+/*
+ * Swiss army knife function to examine currently used and wanted
+ * versus held caps.  Release, flush, ack revoked caps to mds as
+ * appropriate.
+ *
+ *  CHECK_CAPS_NODELAY - caller is delayed work and we should not delay
+ *    cap release further.
+ *  CHECK_CAPS_AUTHONLY - we should only check the auth cap
+ *  CHECK_CAPS_FLUSH - we should flush any dirty caps immediately, without
+ *    further delay.
+ */
+void ceph_check_caps(struct ceph_inode_info *ci, int flags,
+		     struct ceph_mds_session *session)
+{
+	struct ceph_client *client = ceph_inode_to_client(&ci->vfs_inode);
+	struct ceph_mds_client *mdsc = &client->mdsc;
+	struct inode *inode = &ci->vfs_inode;
+	struct ceph_cap *cap;
+	int file_wanted, used;
+	int took_snap_rwsem = 0;             /* true if mdsc->snap_rwsem held */
+	int drop_session_lock = session ? 0 : 1;
+	int want, retain, revoking, flushing = 0;
+	int mds = -1;   /* keep track of how far we've gone through i_caps list
+			   to avoid an infinite loop on retry */
+	struct rb_node *p;
+	int tried_invalidate = 0;
+	int delayed = 0, sent = 0, force_requeue = 0, num;
+	int is_delayed = flags & CHECK_CAPS_NODELAY;
+
+	/* if we are unmounting, flush any unused caps immediately. */
+	if (mdsc->stopping)
+		is_delayed = 1;
+
+	spin_lock(&inode->i_lock);
+
+	if (ci->i_ceph_flags & CEPH_I_FLUSH)
+		flags |= CHECK_CAPS_FLUSH;
+
+	/* flush snaps first time around only */
+	if (!list_empty(&ci->i_cap_snaps))
+		__ceph_flush_snaps(ci, &session);
+	goto retry_locked;
+retry:
+	spin_lock(&inode->i_lock);
+retry_locked:
+	file_wanted = __ceph_caps_file_wanted(ci);
+	used = __ceph_caps_used(ci);
+	want = file_wanted | used;
+
+	retain = want | CEPH_CAP_PIN;
+	if (!mdsc->stopping && inode->i_nlink > 0) {
+		if (want) {
+			retain |= CEPH_CAP_ANY;       /* be greedy */
+		} else {
+			retain |= CEPH_CAP_ANY_SHARED;
+			/*
+			 * keep RD only if we didn't have the file open RW,
+			 * because then the mds would revoke it anyway to
+			 * journal max_size=0.
+			 */
+			if (ci->i_max_size == 0)
+				retain |= CEPH_CAP_ANY_RD;
+		}
+	}
+
+	dout("check_caps %p file_want %s used %s dirty %s flushing %s"
+	     " issued %s retain %s %s%s%s\n", inode,
+	     ceph_cap_string(file_wanted),
+	     ceph_cap_string(used), ceph_cap_string(ci->i_dirty_caps),
+	     ceph_cap_string(ci->i_flushing_caps),
+	     ceph_cap_string(__ceph_caps_issued(ci, NULL)),
+	     ceph_cap_string(retain),
+	     (flags & CHECK_CAPS_AUTHONLY) ? " AUTHONLY" : "",
+	     (flags & CHECK_CAPS_NODELAY) ? " NODELAY" : "",
+	     (flags & CHECK_CAPS_FLUSH) ? " FLUSH" : "");
+
+	/*
+	 * If we no longer need to hold onto old our caps, and we may
+	 * have cached pages, but don't want them, then try to invalidate.
+	 * If we fail, it's because pages are locked.... try again later.
+	 */
+	if ((!is_delayed || mdsc->stopping) &&
+	    ci->i_wrbuffer_ref == 0 &&               /* no dirty pages... */
+	    ci->i_rdcache_gen &&                     /* may have cached pages */
+	    file_wanted == 0 &&                      /* no open files */
+	    !ci->i_truncate_pending &&
+	    !tried_invalidate) {
+		u32 invalidating_gen = ci->i_rdcache_gen;
+		int ret;
+
+		dout("check_caps trying to invalidate on %p\n", inode);
+		spin_unlock(&inode->i_lock);
+		ret = invalidate_inode_pages2(&inode->i_data);
+		spin_lock(&inode->i_lock);
+		if (ret == 0 && invalidating_gen == ci->i_rdcache_gen) {
+			/* success. */
+			ci->i_rdcache_gen = 0;
+			ci->i_rdcache_revoking = 0;
+		} else {
+			dout("check_caps failed to invalidate pages\n");
+			/* we failed to invalidate pages.  check these
+			   caps again later. */
+			force_requeue = 1;
+			__cap_set_timeouts(mdsc, ci);
+		}
+		tried_invalidate = 1;
+		goto retry_locked;
+	}
+
+	num = 0;
+	for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
+		cap = rb_entry(p, struct ceph_cap, ci_node);
+		num++;
+
+		/* avoid looping forever */
+		if (mds >= cap->mds ||
+		    ((flags & CHECK_CAPS_AUTHONLY) && cap != ci->i_auth_cap))
+			continue;
+
+		/* NOTE: no side-effects allowed, until we take s_mutex */
+
+		revoking = cap->implemented & ~cap->issued;
+		if (revoking)
+			dout("mds%d revoking %s\n", cap->mds,
+			     ceph_cap_string(revoking));
+
+		if (cap == ci->i_auth_cap &&
+		    (cap->issued & CEPH_CAP_FILE_WR)) {
+			/* request larger max_size from MDS? */
+			if (ci->i_wanted_max_size > ci->i_max_size &&
+			    ci->i_wanted_max_size > ci->i_requested_max_size) {
+				dout("requesting new max_size\n");
+				goto ack;
+			}
+
+			/* approaching file_max? */
+			if ((inode->i_size << 1) >= ci->i_max_size &&
+			    (ci->i_reported_size << 1) < ci->i_max_size) {
+				dout("i_size approaching max_size\n");
+				goto ack;
+			}
+		}
+		/* flush anything dirty? */
+		if (cap == ci->i_auth_cap && (flags & CHECK_CAPS_FLUSH) &&
+		    ci->i_dirty_caps) {
+			dout("flushing dirty caps\n");
+			goto ack;
+		}
+
+		/* completed revocation? going down and there are no caps? */
+		if (revoking && (revoking & used) == 0) {
+			dout("completed revocation of %s\n",
+			     ceph_cap_string(cap->implemented & ~cap->issued));
+			goto ack;
+		}
+
+		/* want more caps from mds? */
+		if (want & ~(cap->mds_wanted | cap->issued))
+			goto ack;
+
+		/* things we might delay */
+		if ((cap->issued & ~retain) == 0 &&
+		    cap->mds_wanted == want)
+			continue;     /* nope, all good */
+
+		if (is_delayed)
+			goto ack;
+
+		/* delay? */
+		if ((ci->i_ceph_flags & CEPH_I_NODELAY) == 0 &&
+		    time_before(jiffies, ci->i_hold_caps_max)) {
+			dout(" delaying issued %s -> %s, wanted %s -> %s\n",
+			     ceph_cap_string(cap->issued),
+			     ceph_cap_string(cap->issued & retain),
+			     ceph_cap_string(cap->mds_wanted),
+			     ceph_cap_string(want));
+			delayed++;
+			continue;
+		}
+
+ack:
+		if (session && session != cap->session) {
+			dout("oops, wrong session %p mutex\n", session);
+			mutex_unlock(&session->s_mutex);
+			session = NULL;
+		}
+		if (!session) {
+			session = cap->session;
+			if (mutex_trylock(&session->s_mutex) == 0) {
+				dout("inverting session/ino locks on %p\n",
+				     session);
+				spin_unlock(&inode->i_lock);
+				if (took_snap_rwsem) {
+					up_read(&mdsc->snap_rwsem);
+					took_snap_rwsem = 0;
+				}
+				mutex_lock(&session->s_mutex);
+				goto retry;
+			}
+		}
+		/* take snap_rwsem after session mutex */
+		if (!took_snap_rwsem) {
+			if (down_read_trylock(&mdsc->snap_rwsem) == 0) {
+				dout("inverting snap/in locks on %p\n",
+				     inode);
+				spin_unlock(&inode->i_lock);
+				down_read(&mdsc->snap_rwsem);
+				took_snap_rwsem = 1;
+				goto retry;
+			}
+			took_snap_rwsem = 1;
+		}
+
+		if (cap == ci->i_auth_cap && ci->i_dirty_caps) {
+			/* update dirty, flushing bits */
+			flushing = ci->i_dirty_caps;
+			dout(" flushing %s, flushing_caps %s -> %s\n",
+			     ceph_cap_string(flushing),
+			     ceph_cap_string(ci->i_flushing_caps),
+			     ceph_cap_string(ci->i_flushing_caps | flushing));
+			ci->i_flushing_caps |= flushing;
+			ci->i_dirty_caps = 0;
+			__mark_caps_flushing(inode, session);
+		}
+
+		mds = cap->mds;  /* remember mds, so we don't repeat */
+		sent++;
+
+		/* __send_cap drops i_lock */
+		delayed += __send_cap(mdsc, cap, CEPH_CAP_OP_UPDATE, used, want,
+				      retain, flushing, NULL);
+		goto retry; /* retake i_lock and restart our cap scan. */
+	}
+
+	/*
+	 * Reschedule delayed caps release if we delayed anything,
+	 * otherwise cancel.
+	 */
+	if (delayed && is_delayed)
+		force_requeue = 1;   /* __send_cap delayed release; requeue */
+	if (!delayed && !is_delayed)
+		__cap_delay_cancel(mdsc, ci);
+	else if (!is_delayed || force_requeue)
+		__cap_delay_requeue(mdsc, ci);
+
+	spin_unlock(&inode->i_lock);
+
+	if (session && drop_session_lock)
+		mutex_unlock(&session->s_mutex);
+	if (took_snap_rwsem)
+		up_read(&mdsc->snap_rwsem);
+}
+
+/*
+ * Mark caps dirty.  If inode is newly dirty, add to the global dirty
+ * list.
+ */
+int __ceph_mark_dirty_caps(struct ceph_inode_info *ci, int mask)
+{
+	struct ceph_mds_client *mdsc = &ceph_client(ci->vfs_inode.i_sb)->mdsc;
+	struct inode *inode = &ci->vfs_inode;
+	int was = __ceph_caps_dirty(ci);
+	int dirty = 0;
+
+	dout("__mark_dirty_caps %p %s dirty %s -> %s\n", &ci->vfs_inode,
+	     ceph_cap_string(mask), ceph_cap_string(ci->i_dirty_caps),
+	     ceph_cap_string(ci->i_dirty_caps | mask));
+	ci->i_dirty_caps |= mask;
+	if (!was) {
+		dout(" inode %p now dirty\n", &ci->vfs_inode);
+		spin_lock(&mdsc->cap_dirty_lock);
+		list_add(&ci->i_dirty_item, &mdsc->cap_dirty);
+		spin_unlock(&mdsc->cap_dirty_lock);
+		igrab(inode);
+		dirty |= I_DIRTY_SYNC;
+	}
+	if ((was & CEPH_CAP_FILE_BUFFER) &&
+	    (mask & CEPH_CAP_FILE_BUFFER))
+		dirty |= I_DIRTY_DATASYNC;
+	if (dirty)
+		__mark_inode_dirty(inode, dirty);
+	__cap_delay_requeue(mdsc, ci);
+	return was;
+}
+
+/*
+ * Try to flush dirty caps back to the auth mds.
+ */
+static int try_flush_caps(struct inode *inode, struct ceph_mds_session *session,
+			  unsigned *flush_tid)
+{
+	struct ceph_mds_client *mdsc = &ceph_client(inode->i_sb)->mdsc;
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	int unlock_session = session ? 0 : 1;
+	int flushing = 0;
+
+retry:
+	spin_lock(&inode->i_lock);
+	if (ci->i_dirty_caps && ci->i_auth_cap) {
+		struct ceph_cap *cap = ci->i_auth_cap;
+		int used = __ceph_caps_used(ci);
+		int want = __ceph_caps_wanted(ci);
+		int delayed;
+
+		if (!session) {
+			spin_unlock(&inode->i_lock);
+			session = cap->session;
+			mutex_lock(&session->s_mutex);
+			goto retry;
+		}
+		BUG_ON(session != cap->session);
+		if (cap->session->s_state < CEPH_MDS_SESSION_OPEN)
+			goto out;
+
+		__mark_caps_flushing(inode, session);
+
+		flushing = ci->i_dirty_caps;
+		dout(" flushing %s, flushing_caps %s -> %s\n",
+		     ceph_cap_string(flushing),
+		     ceph_cap_string(ci->i_flushing_caps),
+		     ceph_cap_string(ci->i_flushing_caps | flushing));
+		ci->i_flushing_caps |= flushing;
+		ci->i_dirty_caps = 0;
+
+		/* __send_cap drops i_lock */
+		delayed = __send_cap(mdsc, cap, CEPH_CAP_OP_FLUSH, used, want,
+				     cap->issued | cap->implemented, flushing,
+				     flush_tid);
+		if (!delayed)
+			goto out_unlocked;
+
+		spin_lock(&inode->i_lock);
+		__cap_delay_requeue(mdsc, ci);
+	}
+out:
+	spin_unlock(&inode->i_lock);
+out_unlocked:
+	if (session && unlock_session)
+		mutex_unlock(&session->s_mutex);
+	return flushing;
+}
+
+/*
+ * Return true if we've flushed caps through the given flush_tid.
+ */
+static int caps_are_flushed(struct inode *inode, unsigned tid)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	int dirty, i, ret = 1;
+
+	spin_lock(&inode->i_lock);
+	dirty = __ceph_caps_dirty(ci);
+	for (i = 0; i < CEPH_CAP_BITS; i++)
+		if ((ci->i_flushing_caps & (1 << i)) &&
+		    ci->i_cap_flush_tid[i] <= tid) {
+			/* still flushing this bit */
+			ret = 0;
+			break;
+		}
+	spin_unlock(&inode->i_lock);
+	return ret;
+}
+
+/*
+ * Wait on any unsafe replies for the given inode.  First wait on the
+ * newest request, and make that the upper bound.  Then, if there are
+ * more requests, keep waiting on the oldest as long as it is still older
+ * than the original request.
+ */
+static void sync_write_wait(struct inode *inode)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	struct list_head *head = &ci->i_unsafe_writes;
+	struct ceph_osd_request *req;
+	u64 last_tid;
+
+	spin_lock(&ci->i_unsafe_lock);
+	if (list_empty(head))
+		goto out;
+
+	/* set upper bound as _last_ entry in chain */
+	req = list_entry(head->prev, struct ceph_osd_request,
+			 r_unsafe_item);
+	last_tid = req->r_tid;
+
+	do {
+		ceph_osdc_get_request(req);
+		spin_unlock(&ci->i_unsafe_lock);
+		dout("sync_write_wait on tid %llu (until %llu)\n",
+		     req->r_tid, last_tid);
+		wait_for_completion(&req->r_safe_completion);
+		spin_lock(&ci->i_unsafe_lock);
+		ceph_osdc_put_request(req);
+
+		/*
+		 * from here on look at first entry in chain, since we
+		 * only want to wait for anything older than last_tid
+		 */
+		if (list_empty(head))
+			break;
+		req = list_entry(head->next, struct ceph_osd_request,
+				 r_unsafe_item);
+	} while (req->r_tid < last_tid);
+out:
+	spin_unlock(&ci->i_unsafe_lock);
+}
+
+int ceph_fsync(struct file *file, struct dentry *dentry, int datasync)
+{
+	struct inode *inode = dentry->d_inode;
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	unsigned flush_tid;
+	int ret;
+	int dirty;
+
+	dout("fsync %p%s\n", inode, datasync ? " datasync" : "");
+	sync_write_wait(inode);
+
+	ret = filemap_write_and_wait(inode->i_mapping);
+	if (ret < 0)
+		return ret;
+
+	dirty = try_flush_caps(inode, NULL, &flush_tid);
+	dout("fsync dirty caps are %s\n", ceph_cap_string(dirty));
+
+	/*
+	 * only wait on non-file metadata writeback (the mds
+	 * can recover size and mtime, so we don't need to
+	 * wait for that)
+	 */
+	if (!datasync && (dirty & ~CEPH_CAP_ANY_FILE_WR)) {
+		dout("fsync waiting for flush_tid %u\n", flush_tid);
+		ret = wait_event_interruptible(ci->i_cap_wq,
+				       caps_are_flushed(inode, flush_tid));
+	}
+
+	dout("fsync %p%s done\n", inode, datasync ? " datasync" : "");
+	return ret;
+}
+
+/*
+ * Flush any dirty caps back to the mds.  If we aren't asked to wait,
+ * queue inode for flush but don't do so immediately, because we can
+ * get by with fewer MDS messages if we wait for data writeback to
+ * complete first.
+ */
+int ceph_write_inode(struct inode *inode, int wait)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	unsigned flush_tid;
+	int err = 0;
+	int dirty;
+
+	dout("write_inode %p wait=%d\n", inode, wait);
+	if (wait) {
+		dirty = try_flush_caps(inode, NULL, &flush_tid);
+		if (dirty)
+			err = wait_event_interruptible(ci->i_cap_wq,
+				       caps_are_flushed(inode, flush_tid));
+	} else {
+		struct ceph_mds_client *mdsc = &ceph_client(inode->i_sb)->mdsc;
+
+		spin_lock(&inode->i_lock);
+		if (__ceph_caps_dirty(ci))
+			__cap_delay_requeue_front(mdsc, ci);
+		spin_unlock(&inode->i_lock);
+	}
+	return err;
+}
+
+/*
+ * After a recovering MDS goes active, we need to resend any caps
+ * we were flushing.
+ *
+ * Caller holds session->s_mutex.
+ */
+static void kick_flushing_capsnaps(struct ceph_mds_client *mdsc,
+				   struct ceph_mds_session *session)
+{
+	struct ceph_cap_snap *capsnap;
+
+	dout("kick_flushing_capsnaps mds%d\n", session->s_mds);
+	list_for_each_entry(capsnap, &session->s_cap_snaps_flushing,
+			    flushing_item) {
+		struct ceph_inode_info *ci = capsnap->ci;
+		struct inode *inode = &ci->vfs_inode;
+		struct ceph_cap *cap;
+
+		spin_lock(&inode->i_lock);
+		cap = ci->i_auth_cap;
+		if (cap && cap->session == session) {
+			dout("kick_flushing_caps %p cap %p capsnap %p\n", inode,
+			     cap, capsnap);
+			__ceph_flush_snaps(ci, &session);
+		} else {
+			pr_err("%p auth cap %p not mds%d ???\n", inode,
+			       cap, session->s_mds);
+			spin_unlock(&inode->i_lock);
+		}
+	}
+}
+
+void ceph_kick_flushing_caps(struct ceph_mds_client *mdsc,
+			     struct ceph_mds_session *session)
+{
+	struct ceph_inode_info *ci;
+
+	kick_flushing_capsnaps(mdsc, session);
+
+	dout("kick_flushing_caps mds%d\n", session->s_mds);
+	list_for_each_entry(ci, &session->s_cap_flushing, i_flushing_item) {
+		struct inode *inode = &ci->vfs_inode;
+		struct ceph_cap *cap;
+		int delayed = 0;
+
+		spin_lock(&inode->i_lock);
+		cap = ci->i_auth_cap;
+		if (cap && cap->session == session) {
+			dout("kick_flushing_caps %p cap %p %s\n", inode,
+			     cap, ceph_cap_string(ci->i_flushing_caps));
+			delayed = __send_cap(mdsc, cap, CEPH_CAP_OP_FLUSH,
+					     __ceph_caps_used(ci),
+					     __ceph_caps_wanted(ci),
+					     cap->issued | cap->implemented,
+					     ci->i_flushing_caps, NULL);
+			if (delayed) {
+				spin_lock(&inode->i_lock);
+				__cap_delay_requeue(mdsc, ci);
+				spin_unlock(&inode->i_lock);
+			}
+		} else {
+			pr_err("%p auth cap %p not mds%d ???\n", inode,
+			       cap, session->s_mds);
+			spin_unlock(&inode->i_lock);
+		}
+	}
+}
+
+
+/*
+ * Take references to capabilities we hold, so that we don't release
+ * them to the MDS prematurely.
+ *
+ * Protected by i_lock.
+ */
+static void __take_cap_refs(struct ceph_inode_info *ci, int got)
+{
+	if (got & CEPH_CAP_PIN)
+		ci->i_pin_ref++;
+	if (got & CEPH_CAP_FILE_RD)
+		ci->i_rd_ref++;
+	if (got & CEPH_CAP_FILE_CACHE)
+		ci->i_rdcache_ref++;
+	if (got & CEPH_CAP_FILE_WR)
+		ci->i_wr_ref++;
+	if (got & CEPH_CAP_FILE_BUFFER) {
+		if (ci->i_wrbuffer_ref == 0)
+			igrab(&ci->vfs_inode);
+		ci->i_wrbuffer_ref++;
+		dout("__take_cap_refs %p wrbuffer %d -> %d (?)\n",
+		     &ci->vfs_inode, ci->i_wrbuffer_ref-1, ci->i_wrbuffer_ref);
+	}
+}
+
+/*
+ * Try to grab cap references.  Specify those refs we @want, and the
+ * minimal set we @need.  Also include the larger offset we are writing
+ * to (when applicable), and check against max_size here as well.
+ * Note that caller is responsible for ensuring max_size increases are
+ * requested from the MDS.
+ */
+static int try_get_cap_refs(struct ceph_inode_info *ci, int need, int want,
+			    int *got, loff_t endoff, int *check_max, int *err)
+{
+	struct inode *inode = &ci->vfs_inode;
+	int ret = 0;
+	int have, implemented;
+
+	dout("get_cap_refs %p need %s want %s\n", inode,
+	     ceph_cap_string(need), ceph_cap_string(want));
+	spin_lock(&inode->i_lock);
+
+	/* make sure we _have_ some caps! */
+	if (!__ceph_is_any_caps(ci)) {
+		dout("get_cap_refs %p no real caps\n", inode);
+		*err = -EBADF;
+		ret = 1;
+		goto out;
+	}
+
+	if (need & CEPH_CAP_FILE_WR) {
+		if (endoff >= 0 && endoff > (loff_t)ci->i_max_size) {
+			dout("get_cap_refs %p endoff %llu > maxsize %llu\n",
+			     inode, endoff, ci->i_max_size);
+			if (endoff > ci->i_wanted_max_size) {
+				*check_max = 1;
+				ret = 1;
+			}
+			goto out;
+		}
+		/*
+		 * If a sync write is in progress, we must wait, so that we
+		 * can get a final snapshot value for size+mtime.
+		 */
+		if (__ceph_have_pending_cap_snap(ci)) {
+			dout("get_cap_refs %p cap_snap_pending\n", inode);
+			goto out;
+		}
+	}
+	have = __ceph_caps_issued(ci, &implemented);
+
+	/*
+	 * disallow writes while a truncate is pending
+	 */
+	if (ci->i_truncate_pending)
+		have &= ~CEPH_CAP_FILE_WR;
+
+	if ((have & need) == need) {
+		/*
+		 * Look at (implemented & ~have & not) so that we keep waiting
+		 * on transition from wanted -> needed caps.  This is needed
+		 * for WRBUFFER|WR -> WR to avoid a new WR sync write from
+		 * going before a prior buffered writeback happens.
+		 */
+		int not = want & ~(have & need);
+		int revoking = implemented & ~have;
+		dout("get_cap_refs %p have %s but not %s (revoking %s)\n",
+		     inode, ceph_cap_string(have), ceph_cap_string(not),
+		     ceph_cap_string(revoking));
+		if ((revoking & not) == 0) {
+			*got = need | (have & want);
+			__take_cap_refs(ci, *got);
+			ret = 1;
+		}
+	} else {
+		dout("get_cap_refs %p have %s needed %s\n", inode,
+		     ceph_cap_string(have), ceph_cap_string(need));
+	}
+out:
+	spin_unlock(&inode->i_lock);
+	dout("get_cap_refs %p ret %d got %s\n", inode,
+	     ret, ceph_cap_string(*got));
+	return ret;
+}
+
+/*
+ * Check the offset we are writing up to against our current
+ * max_size.  If necessary, tell the MDS we want to write to
+ * a larger offset.
+ */
+static void check_max_size(struct inode *inode, loff_t endoff)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	int check = 0;
+
+	/* do we need to explicitly request a larger max_size? */
+	spin_lock(&inode->i_lock);
+	if ((endoff >= ci->i_max_size ||
+	     endoff > (inode->i_size << 1)) &&
+	    endoff > ci->i_wanted_max_size) {
+		dout("write %p at large endoff %llu, req max_size\n",
+		     inode, endoff);
+		ci->i_wanted_max_size = endoff;
+		check = 1;
+	}
+	spin_unlock(&inode->i_lock);
+	if (check)
+		ceph_check_caps(ci, CHECK_CAPS_AUTHONLY, NULL);
+}
+
+/*
+ * Wait for caps, and take cap references.  If we can't get a WR cap
+ * due to a small max_size, make sure we check_max_size (and possibly
+ * ask the mds) so we don't get hung up indefinitely.
+ */
+int ceph_get_caps(struct ceph_inode_info *ci, int need, int want, int *got,
+		  loff_t endoff)
+{
+	int check_max, ret, err;
+
+retry:
+	if (endoff > 0)
+		check_max_size(&ci->vfs_inode, endoff);
+	check_max = 0;
+	err = 0;
+	ret = wait_event_interruptible(ci->i_cap_wq,
+				       try_get_cap_refs(ci, need, want,
+							got, endoff,
+							&check_max, &err));
+	if (err)
+		ret = err;
+	if (check_max)
+		goto retry;
+	return ret;
+}
+
+/*
+ * Take cap refs.  Caller must already know we hold at least one ref
+ * on the caps in question or we don't know this is safe.
+ */
+void ceph_get_cap_refs(struct ceph_inode_info *ci, int caps)
+{
+	spin_lock(&ci->vfs_inode.i_lock);
+	__take_cap_refs(ci, caps);
+	spin_unlock(&ci->vfs_inode.i_lock);
+}
+
+/*
+ * Release cap refs.
+ *
+ * If we released the last ref on any given cap, call ceph_check_caps
+ * to release (or schedule a release).
+ *
+ * If we are releasing a WR cap (from a sync write), finalize any affected
+ * cap_snap, and wake up any waiters.
+ */
+void ceph_put_cap_refs(struct ceph_inode_info *ci, int had)
+{
+	struct inode *inode = &ci->vfs_inode;
+	int last = 0, put = 0, flushsnaps = 0, wake = 0;
+	struct ceph_cap_snap *capsnap;
+
+	spin_lock(&inode->i_lock);
+	if (had & CEPH_CAP_PIN)
+		--ci->i_pin_ref;
+	if (had & CEPH_CAP_FILE_RD)
+		if (--ci->i_rd_ref == 0)
+			last++;
+	if (had & CEPH_CAP_FILE_CACHE)
+		if (--ci->i_rdcache_ref == 0)
+			last++;
+	if (had & CEPH_CAP_FILE_BUFFER) {
+		if (--ci->i_wrbuffer_ref == 0) {
+			last++;
+			put++;
+		}
+		dout("put_cap_refs %p wrbuffer %d -> %d (?)\n",
+		     inode, ci->i_wrbuffer_ref+1, ci->i_wrbuffer_ref);
+	}
+	if (had & CEPH_CAP_FILE_WR)
+		if (--ci->i_wr_ref == 0) {
+			last++;
+			if (!list_empty(&ci->i_cap_snaps)) {
+				capsnap = list_first_entry(&ci->i_cap_snaps,
+						     struct ceph_cap_snap,
+						     ci_item);
+				if (capsnap->writing) {
+					capsnap->writing = 0;
+					flushsnaps =
+						__ceph_finish_cap_snap(ci,
+								       capsnap);
+					wake = 1;
+				}
+			}
+		}
+	spin_unlock(&inode->i_lock);
+
+	dout("put_cap_refs %p had %s %s\n", inode, ceph_cap_string(had),
+	     last ? "last" : "");
+
+	if (last && !flushsnaps)
+		ceph_check_caps(ci, 0, NULL);
+	else if (flushsnaps)
+		ceph_flush_snaps(ci);
+	if (wake)
+		wake_up(&ci->i_cap_wq);
+	if (put)
+		iput(inode);
+}
+
+/*
+ * Release @nr WRBUFFER refs on dirty pages for the given @snapc snap
+ * context.  Adjust per-snap dirty page accounting as appropriate.
+ * Once all dirty data for a cap_snap is flushed, flush snapped file
+ * metadata back to the MDS.  If we dropped the last ref, call
+ * ceph_check_caps.
+ */
+void ceph_put_wrbuffer_cap_refs(struct ceph_inode_info *ci, int nr,
+				struct ceph_snap_context *snapc)
+{
+	struct inode *inode = &ci->vfs_inode;
+	int last = 0;
+	int last_snap = 0;
+	int found = 0;
+	struct ceph_cap_snap *capsnap = NULL;
+
+	spin_lock(&inode->i_lock);
+	ci->i_wrbuffer_ref -= nr;
+	last = !ci->i_wrbuffer_ref;
+
+	if (ci->i_head_snapc == snapc) {
+		ci->i_wrbuffer_ref_head -= nr;
+		if (!ci->i_wrbuffer_ref_head) {
+			ceph_put_snap_context(ci->i_head_snapc);
+			ci->i_head_snapc = NULL;
+		}
+		dout("put_wrbuffer_cap_refs on %p head %d/%d -> %d/%d %s\n",
+		     inode,
+		     ci->i_wrbuffer_ref+nr, ci->i_wrbuffer_ref_head+nr,
+		     ci->i_wrbuffer_ref, ci->i_wrbuffer_ref_head,
+		     last ? " LAST" : "");
+	} else {
+		list_for_each_entry(capsnap, &ci->i_cap_snaps, ci_item) {
+			if (capsnap->context == snapc) {
+				found = 1;
+				capsnap->dirty_pages -= nr;
+				last_snap = !capsnap->dirty_pages;
+				break;
+			}
+		}
+		BUG_ON(!found);
+		dout("put_wrbuffer_cap_refs on %p cap_snap %p "
+		     " snap %lld %d/%d -> %d/%d %s%s\n",
+		     inode, capsnap, capsnap->context->seq,
+		     ci->i_wrbuffer_ref+nr, capsnap->dirty_pages + nr,
+		     ci->i_wrbuffer_ref, capsnap->dirty_pages,
+		     last ? " (wrbuffer last)" : "",
+		     last_snap ? " (capsnap last)" : "");
+	}
+
+	spin_unlock(&inode->i_lock);
+
+	if (last) {
+		ceph_check_caps(ci, CHECK_CAPS_AUTHONLY, NULL);
+		iput(inode);
+	} else if (last_snap) {
+		ceph_flush_snaps(ci);
+		wake_up(&ci->i_cap_wq);
+	}
+}
+
+/*
+ * Handle a cap GRANT message from the MDS.  (Note that a GRANT may
+ * actually be a revocation if it specifies a smaller cap set.)
+ *
+ * caller holds s_mutex.
+ * return value:
+ *  0 - ok
+ *  1 - check_caps on auth cap only (writeback)
+ *  2 - check_caps (ack revoke)
+ */
+static int handle_cap_grant(struct inode *inode, struct ceph_mds_caps *grant,
+			    struct ceph_mds_session *session,
+			    struct ceph_cap *cap,
+			    struct ceph_buffer *xattr_buf)
+	__releases(inode->i_lock)
+
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	int mds = session->s_mds;
+	int seq = le32_to_cpu(grant->seq);
+	int newcaps = le32_to_cpu(grant->caps);
+	int issued, implemented, used, wanted, dirty;
+	u64 size = le64_to_cpu(grant->size);
+	u64 max_size = le64_to_cpu(grant->max_size);
+	struct timespec mtime, atime, ctime;
+	int reply = 0;
+	int wake = 0;
+	int writeback = 0;
+	int revoked_rdcache = 0;
+	int invalidate_async = 0;
+	int tried_invalidate = 0;
+	int ret;
+
+	dout("handle_cap_grant inode %p cap %p mds%d seq %d %s\n",
+	     inode, cap, mds, seq, ceph_cap_string(newcaps));
+	dout(" size %llu max_size %llu, i_size %llu\n", size, max_size,
+		inode->i_size);
+
+	/*
+	 * If CACHE is being revoked, and we have no dirty buffers,
+	 * try to invalidate (once).  (If there are dirty buffers, we
+	 * will invalidate _after_ writeback.)
+	 */
+restart:
+	if (((cap->issued & ~newcaps) & CEPH_CAP_FILE_CACHE) &&
+	    !ci->i_wrbuffer_ref && !tried_invalidate) {
+		dout("CACHE invalidation\n");
+		spin_unlock(&inode->i_lock);
+		tried_invalidate = 1;
+
+		ret = invalidate_inode_pages2(&inode->i_data);
+		spin_lock(&inode->i_lock);
+		if (ret < 0) {
+			/* there were locked pages.. invalidate later
+			   in a separate thread. */
+			if (ci->i_rdcache_revoking != ci->i_rdcache_gen) {
+				invalidate_async = 1;
+				ci->i_rdcache_revoking = ci->i_rdcache_gen;
+			}
+		} else {
+			/* we successfully invalidated those pages */
+			revoked_rdcache = 1;
+			ci->i_rdcache_gen = 0;
+			ci->i_rdcache_revoking = 0;
+		}
+		goto restart;
+	}
+
+	/* side effects now are allowed */
+
+	issued = __ceph_caps_issued(ci, &implemented);
+	issued |= implemented | __ceph_caps_dirty(ci);
+
+	cap->gen = session->s_cap_gen;
+
+	__check_cap_issue(ci, cap, newcaps);
+
+	if ((issued & CEPH_CAP_AUTH_EXCL) == 0) {
+		inode->i_mode = le32_to_cpu(grant->mode);
+		inode->i_uid = le32_to_cpu(grant->uid);
+		inode->i_gid = le32_to_cpu(grant->gid);
+		dout("%p mode 0%o uid.gid %d.%d\n", inode, inode->i_mode,
+		     inode->i_uid, inode->i_gid);
+	}
+
+	if ((issued & CEPH_CAP_LINK_EXCL) == 0)
+		inode->i_nlink = le32_to_cpu(grant->nlink);
+
+	if ((issued & CEPH_CAP_XATTR_EXCL) == 0 && grant->xattr_len) {
+		int len = le32_to_cpu(grant->xattr_len);
+		u64 version = le64_to_cpu(grant->xattr_version);
+
+		if (version > ci->i_xattrs.version) {
+			dout(" got new xattrs v%llu on %p len %d\n",
+			     version, inode, len);
+			if (ci->i_xattrs.blob)
+				ceph_buffer_put(ci->i_xattrs.blob);
+			ci->i_xattrs.blob = ceph_buffer_get(xattr_buf);
+			ci->i_xattrs.version = version;
+		}
+	}
+
+	/* size/ctime/mtime/atime? */
+	ceph_fill_file_size(inode, issued,
+			    le32_to_cpu(grant->truncate_seq),
+			    le64_to_cpu(grant->truncate_size), size);
+	ceph_decode_timespec(&mtime, &grant->mtime);
+	ceph_decode_timespec(&atime, &grant->atime);
+	ceph_decode_timespec(&ctime, &grant->ctime);
+	ceph_fill_file_time(inode, issued,
+			    le32_to_cpu(grant->time_warp_seq), &ctime, &mtime,
+			    &atime);
+
+	/* max size increase? */
+	if (max_size != ci->i_max_size) {
+		dout("max_size %lld -> %llu\n", ci->i_max_size, max_size);
+		ci->i_max_size = max_size;
+		if (max_size >= ci->i_wanted_max_size) {
+			ci->i_wanted_max_size = 0;  /* reset */
+			ci->i_requested_max_size = 0;
+		}
+		wake = 1;
+	}
+
+	/* check cap bits */
+	wanted = __ceph_caps_wanted(ci);
+	used = __ceph_caps_used(ci);
+	dirty = __ceph_caps_dirty(ci);
+	dout(" my wanted = %s, used = %s, dirty %s\n",
+	     ceph_cap_string(wanted),
+	     ceph_cap_string(used),
+	     ceph_cap_string(dirty));
+	if (wanted != le32_to_cpu(grant->wanted)) {
+		dout("mds wanted %s -> %s\n",
+		     ceph_cap_string(le32_to_cpu(grant->wanted)),
+		     ceph_cap_string(wanted));
+		grant->wanted = cpu_to_le32(wanted);
+	}
+
+	cap->seq = seq;
+
+	/* file layout may have changed */
+	ci->i_layout = grant->layout;
+
+	/* revocation, grant, or no-op? */
+	if (cap->issued & ~newcaps) {
+		dout("revocation: %s -> %s\n", ceph_cap_string(cap->issued),
+		     ceph_cap_string(newcaps));
+		if ((used & ~newcaps) & CEPH_CAP_FILE_BUFFER)
+			writeback = 1; /* will delay ack */
+		else if (dirty & ~newcaps)
+			reply = 1;     /* initiate writeback in check_caps */
+		else if (((used & ~newcaps) & CEPH_CAP_FILE_CACHE) == 0 ||
+			   revoked_rdcache)
+			reply = 2;     /* send revoke ack in check_caps */
+		cap->issued = newcaps;
+	} else if (cap->issued == newcaps) {
+		dout("caps unchanged: %s -> %s\n",
+		     ceph_cap_string(cap->issued), ceph_cap_string(newcaps));
+	} else {
+		dout("grant: %s -> %s\n", ceph_cap_string(cap->issued),
+		     ceph_cap_string(newcaps));
+		cap->issued = newcaps;
+		cap->implemented |= newcaps; /* add bits only, to
+					      * avoid stepping on a
+					      * pending revocation */
+		wake = 1;
+	}
+
+	spin_unlock(&inode->i_lock);
+	if (writeback) {
+		/*
+		 * queue inode for writeback: we can't actually call
+		 * filemap_write_and_wait, etc. from message handler
+		 * context.
+		 */
+		dout("queueing %p for writeback\n", inode);
+		if (ceph_queue_writeback(inode))
+			igrab(inode);
+	}
+	if (invalidate_async) {
+		dout("queueing %p for page invalidation\n", inode);
+		if (ceph_queue_page_invalidation(inode))
+			igrab(inode);
+	}
+	if (wake)
+		wake_up(&ci->i_cap_wq);
+	return reply;
+}
+
+/*
+ * Handle FLUSH_ACK from MDS, indicating that metadata we sent to the
+ * MDS has been safely committed.
+ */
+static void handle_cap_flush_ack(struct inode *inode,
+				 struct ceph_mds_caps *m,
+				 struct ceph_mds_session *session,
+				 struct ceph_cap *cap)
+	__releases(inode->i_lock)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	struct ceph_mds_client *mdsc = &ceph_client(inode->i_sb)->mdsc;
+	unsigned seq = le32_to_cpu(m->seq);
+	int dirty = le32_to_cpu(m->dirty);
+	int cleaned = 0;
+	u64 flush_tid = le64_to_cpu(m->client_tid);
+	int old_dirty = 0, new_dirty = 0;
+	int i;
+
+	for (i = 0; i < CEPH_CAP_BITS; i++)
+		if ((dirty & (1 << i)) &&
+		    flush_tid == ci->i_cap_flush_tid[i])
+			cleaned |= 1 << i;
+
+	dout("handle_cap_flush_ack inode %p mds%d seq %d on %s cleaned %s,"
+	     " flushing %s -> %s\n",
+	     inode, session->s_mds, seq, ceph_cap_string(dirty),
+	     ceph_cap_string(cleaned), ceph_cap_string(ci->i_flushing_caps),
+	     ceph_cap_string(ci->i_flushing_caps & ~cleaned));
+
+	if (ci->i_flushing_caps == (ci->i_flushing_caps & ~cleaned))
+		goto out;
+
+	old_dirty = ci->i_dirty_caps | ci->i_flushing_caps;
+	ci->i_flushing_caps &= ~cleaned;
+	new_dirty = ci->i_dirty_caps | ci->i_flushing_caps;
+
+	spin_lock(&mdsc->cap_dirty_lock);
+	if (ci->i_flushing_caps == 0) {
+		list_del_init(&ci->i_flushing_item);
+		if (!list_empty(&session->s_cap_flushing))
+			dout(" mds%d still flushing cap on %p\n",
+			     session->s_mds,
+			     &list_entry(session->s_cap_flushing.next,
+					 struct ceph_inode_info,
+					 i_flushing_item)->vfs_inode);
+		mdsc->num_cap_flushing--;
+		wake_up(&mdsc->cap_flushing_wq);
+		dout(" inode %p now !flushing\n", inode);
+	}
+	if (old_dirty && !new_dirty) {
+		dout(" inode %p now clean\n", inode);
+		list_del_init(&ci->i_dirty_item);
+	}
+	spin_unlock(&mdsc->cap_dirty_lock);
+	wake_up(&ci->i_cap_wq);
+
+out:
+	spin_unlock(&inode->i_lock);
+	if (old_dirty && !new_dirty)
+		iput(inode);
+}
+
+/*
+ * Handle FLUSHSNAP_ACK.  MDS has flushed snap data to disk and we can
+ * throw away our cap_snap.
+ *
+ * Caller hold s_mutex.
+ */
+static void handle_cap_flushsnap_ack(struct inode *inode,
+				     struct ceph_mds_caps *m,
+				     struct ceph_mds_session *session)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	u64 follows = le64_to_cpu(m->snap_follows);
+	u64 flush_tid = le64_to_cpu(m->client_tid);
+	struct ceph_cap_snap *capsnap;
+	int drop = 0;
+
+	dout("handle_cap_flushsnap_ack inode %p ci %p mds%d follows %lld\n",
+	     inode, ci, session->s_mds, follows);
+
+	spin_lock(&inode->i_lock);
+	list_for_each_entry(capsnap, &ci->i_cap_snaps, ci_item) {
+		if (capsnap->follows == follows) {
+			if (capsnap->flush_tid != flush_tid) {
+				dout(" cap_snap %p follows %lld tid %lld !="
+				     " %lld\n", capsnap, follows,
+				     flush_tid, capsnap->flush_tid);
+				break;
+			}
+			WARN_ON(capsnap->dirty_pages || capsnap->writing);
+			dout(" removing cap_snap %p follows %lld\n",
+			     capsnap, follows);
+			ceph_put_snap_context(capsnap->context);
+			list_del(&capsnap->ci_item);
+			list_del(&capsnap->flushing_item);
+			ceph_put_cap_snap(capsnap);
+			drop = 1;
+			break;
+		} else {
+			dout(" skipping cap_snap %p follows %lld\n",
+			     capsnap, capsnap->follows);
+		}
+	}
+	spin_unlock(&inode->i_lock);
+	if (drop)
+		iput(inode);
+}
+
+/*
+ * Handle TRUNC from MDS, indicating file truncation.
+ *
+ * caller hold s_mutex.
+ */
+static void handle_cap_trunc(struct inode *inode,
+			     struct ceph_mds_caps *trunc,
+			     struct ceph_mds_session *session)
+	__releases(inode->i_lock)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	int mds = session->s_mds;
+	int seq = le32_to_cpu(trunc->seq);
+	u32 truncate_seq = le32_to_cpu(trunc->truncate_seq);
+	u64 truncate_size = le64_to_cpu(trunc->truncate_size);
+	u64 size = le64_to_cpu(trunc->size);
+	int implemented = 0;
+	int dirty = __ceph_caps_dirty(ci);
+	int issued = __ceph_caps_issued(ceph_inode(inode), &implemented);
+	int queue_trunc = 0;
+
+	issued |= implemented | dirty;
+
+	dout("handle_cap_trunc inode %p mds%d seq %d to %lld seq %d\n",
+	     inode, mds, seq, truncate_size, truncate_seq);
+	queue_trunc = ceph_fill_file_size(inode, issued,
+					  truncate_seq, truncate_size, size);
+	spin_unlock(&inode->i_lock);
+
+	if (queue_trunc)
+		if (queue_work(ceph_client(inode->i_sb)->trunc_wq,
+			       &ci->i_vmtruncate_work))
+			igrab(inode);
+}
+
+/*
+ * Handle EXPORT from MDS.  Cap is being migrated _from_ this mds to a
+ * different one.  If we are the most recent migration we've seen (as
+ * indicated by mseq), make note of the migrating cap bits for the
+ * duration (until we see the corresponding IMPORT).
+ *
+ * caller holds s_mutex
+ */
+static void handle_cap_export(struct inode *inode, struct ceph_mds_caps *ex,
+			      struct ceph_mds_session *session)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	int mds = session->s_mds;
+	unsigned mseq = le32_to_cpu(ex->migrate_seq);
+	struct ceph_cap *cap = NULL, *t;
+	struct rb_node *p;
+	int remember = 1;
+
+	dout("handle_cap_export inode %p ci %p mds%d mseq %d\n",
+	     inode, ci, mds, mseq);
+
+	spin_lock(&inode->i_lock);
+
+	/* make sure we haven't seen a higher mseq */
+	for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
+		t = rb_entry(p, struct ceph_cap, ci_node);
+		if (ceph_seq_cmp(t->mseq, mseq) > 0) {
+			dout(" higher mseq on cap from mds%d\n",
+			     t->session->s_mds);
+			remember = 0;
+		}
+		if (t->session->s_mds == mds)
+			cap = t;
+	}
+
+	if (cap) {
+		if (remember) {
+			/* make note */
+			ci->i_cap_exporting_mds = mds;
+			ci->i_cap_exporting_mseq = mseq;
+			ci->i_cap_exporting_issued = cap->issued;
+		}
+		__ceph_remove_cap(cap, NULL);
+	} else {
+		WARN_ON(!cap);
+	}
+
+	spin_unlock(&inode->i_lock);
+}
+
+/*
+ * Handle cap IMPORT.  If there are temp bits from an older EXPORT,
+ * clean them up.
+ *
+ * caller holds s_mutex.
+ */
+static void handle_cap_import(struct ceph_mds_client *mdsc,
+			      struct inode *inode, struct ceph_mds_caps *im,
+			      struct ceph_mds_session *session,
+			      void *snaptrace, int snaptrace_len)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	int mds = session->s_mds;
+	unsigned issued = le32_to_cpu(im->caps);
+	unsigned wanted = le32_to_cpu(im->wanted);
+	unsigned seq = le32_to_cpu(im->seq);
+	unsigned mseq = le32_to_cpu(im->migrate_seq);
+	u64 realmino = le64_to_cpu(im->realm);
+	u64 cap_id = le64_to_cpu(im->cap_id);
+
+	if (ci->i_cap_exporting_mds >= 0 &&
+	    ceph_seq_cmp(ci->i_cap_exporting_mseq, mseq) < 0) {
+		dout("handle_cap_import inode %p ci %p mds%d mseq %d"
+		     " - cleared exporting from mds%d\n",
+		     inode, ci, mds, mseq,
+		     ci->i_cap_exporting_mds);
+		ci->i_cap_exporting_issued = 0;
+		ci->i_cap_exporting_mseq = 0;
+		ci->i_cap_exporting_mds = -1;
+	} else {
+		dout("handle_cap_import inode %p ci %p mds%d mseq %d\n",
+		     inode, ci, mds, mseq);
+	}
+
+	down_write(&mdsc->snap_rwsem);
+	ceph_update_snap_trace(mdsc, snaptrace, snaptrace+snaptrace_len,
+			       false);
+	downgrade_write(&mdsc->snap_rwsem);
+	ceph_add_cap(inode, session, cap_id, -1,
+		     issued, wanted, seq, mseq, realmino, CEPH_CAP_FLAG_AUTH,
+		     NULL /* no caps context */);
+	try_flush_caps(inode, session, NULL);
+	up_read(&mdsc->snap_rwsem);
+}
+
+/*
+ * Handle a caps message from the MDS.
+ *
+ * Identify the appropriate session, inode, and call the right handler
+ * based on the cap op.
+ */
+void ceph_handle_caps(struct ceph_mds_session *session,
+		      struct ceph_msg *msg)
+{
+	struct ceph_mds_client *mdsc = session->s_mdsc;
+	struct super_block *sb = mdsc->client->sb;
+	struct inode *inode;
+	struct ceph_cap *cap;
+	struct ceph_mds_caps *h;
+	int mds = le64_to_cpu(msg->hdr.src.name.num);
+	int op;
+	u32 seq;
+	struct ceph_vino vino;
+	u64 cap_id;
+	u64 size, max_size;
+	int check_caps = 0;
+	int r;
+
+	dout("handle_caps from mds%d\n", mds);
+
+	/* decode */
+	if (msg->front.iov_len < sizeof(*h))
+		goto bad;
+	h = msg->front.iov_base;
+	op = le32_to_cpu(h->op);
+	vino.ino = le64_to_cpu(h->ino);
+	vino.snap = CEPH_NOSNAP;
+	cap_id = le64_to_cpu(h->cap_id);
+	seq = le32_to_cpu(h->seq);
+	size = le64_to_cpu(h->size);
+	max_size = le64_to_cpu(h->max_size);
+
+	mutex_lock(&session->s_mutex);
+	session->s_seq++;
+	dout(" mds%d seq %lld cap seq %u\n", session->s_mds, session->s_seq,
+	     (unsigned)seq);
+
+	/* lookup ino */
+	inode = ceph_find_inode(sb, vino);
+	dout(" op %s ino %llx.%llx inode %p\n", ceph_cap_op_name(op), vino.ino,
+	     vino.snap, inode);
+	if (!inode) {
+		dout(" i don't have ino %llx\n", vino.ino);
+		goto done;
+	}
+
+	/* these will work even if we don't have a cap yet */
+	switch (op) {
+	case CEPH_CAP_OP_FLUSHSNAP_ACK:
+		handle_cap_flushsnap_ack(inode, h, session);
+		goto done;
+
+	case CEPH_CAP_OP_EXPORT:
+		handle_cap_export(inode, h, session);
+		goto done;
+
+	case CEPH_CAP_OP_IMPORT:
+		handle_cap_import(mdsc, inode, h, session,
+				  msg->middle,
+				  le32_to_cpu(h->snap_trace_len));
+		check_caps = 1; /* we may have sent a RELEASE to the old auth */
+		goto done;
+	}
+
+	/* the rest require a cap */
+	spin_lock(&inode->i_lock);
+	cap = __get_cap_for_mds(ceph_inode(inode), mds);
+	if (!cap) {
+		dout("no cap on %p ino %llx.%llx from mds%d, releasing\n",
+		     inode, ceph_ino(inode), ceph_snap(inode), mds);
+		spin_unlock(&inode->i_lock);
+		goto done;
+	}
+
+	/* note that each of these drops i_lock for us */
+	switch (op) {
+	case CEPH_CAP_OP_REVOKE:
+	case CEPH_CAP_OP_GRANT:
+		r = handle_cap_grant(inode, h, session, cap, msg->middle);
+		if (r == 1)
+			ceph_check_caps(ceph_inode(inode),
+					CHECK_CAPS_NODELAY|CHECK_CAPS_AUTHONLY,
+					session);
+		else if (r == 2)
+			ceph_check_caps(ceph_inode(inode),
+					CHECK_CAPS_NODELAY,
+					session);
+		break;
+
+	case CEPH_CAP_OP_FLUSH_ACK:
+		handle_cap_flush_ack(inode, h, session, cap);
+		break;
+
+	case CEPH_CAP_OP_TRUNC:
+		handle_cap_trunc(inode, h, session);
+		break;
+
+	default:
+		spin_unlock(&inode->i_lock);
+		pr_err("ceph_handle_caps: unknown cap op %d %s\n", op,
+		       ceph_cap_op_name(op));
+	}
+
+done:
+	mutex_unlock(&session->s_mutex);
+
+	if (check_caps)
+		ceph_check_caps(ceph_inode(inode), CHECK_CAPS_NODELAY, NULL);
+	if (inode)
+		iput(inode);
+	return;
+
+bad:
+	pr_err("ceph_handle_caps: corrupt message\n");
+	return;
+}
+
+/*
+ * Delayed work handler to process end of delayed cap release LRU list.
+ */
+void ceph_check_delayed_caps(struct ceph_mds_client *mdsc, int flushdirty)
+{
+	struct ceph_inode_info *ci;
+	int flags = CHECK_CAPS_NODELAY;
+
+	if (flushdirty)
+		flags |= CHECK_CAPS_FLUSH;
+
+	dout("check_delayed_caps\n");
+	while (1) {
+		spin_lock(&mdsc->cap_delay_lock);
+		if (list_empty(&mdsc->cap_delay_list))
+			break;
+		ci = list_first_entry(&mdsc->cap_delay_list,
+				      struct ceph_inode_info,
+				      i_cap_delay_list);
+		if ((ci->i_ceph_flags & CEPH_I_FLUSH) == 0 &&
+		    time_before(jiffies, ci->i_hold_caps_max))
+			break;
+		list_del_init(&ci->i_cap_delay_list);
+		spin_unlock(&mdsc->cap_delay_lock);
+		dout("check_delayed_caps on %p\n", &ci->vfs_inode);
+		ceph_check_caps(ci, flags, NULL);
+	}
+	spin_unlock(&mdsc->cap_delay_lock);
+}
+
+/*
+ * Drop open file reference.  If we were the last open file,
+ * we may need to release capabilities to the MDS (or schedule
+ * their delayed release).
+ */
+void ceph_put_fmode(struct ceph_inode_info *ci, int fmode)
+{
+	struct inode *inode = &ci->vfs_inode;
+	int last = 0;
+
+	spin_lock(&inode->i_lock);
+	dout("put_fmode %p fmode %d %d -> %d\n", inode, fmode,
+	     ci->i_nr_by_mode[fmode], ci->i_nr_by_mode[fmode]-1);
+	BUG_ON(ci->i_nr_by_mode[fmode] == 0);
+	if (--ci->i_nr_by_mode[fmode] == 0)
+		last++;
+	spin_unlock(&inode->i_lock);
+
+	if (last && ci->i_vino.snap == CEPH_NOSNAP)
+		ceph_check_caps(ci, 0, NULL);
+}
+
+/*
+ * Helpers for embedding cap and dentry lease releases into mds
+ * requests.
+ *
+ * @force is used by dentry_release (below) to force inclusion of a
+ * record for the directory inode, even when there aren't any caps to
+ * drop.
+ */
+int ceph_encode_inode_release(void **p, struct inode *inode,
+			      int mds, int drop, int unless, int force)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	struct ceph_cap *cap;
+	struct ceph_mds_request_release *rel = *p;
+	int ret = 0;
+
+	dout("encode_inode_release %p mds%d drop %s unless %s\n", inode,
+	     mds, ceph_cap_string(drop), ceph_cap_string(unless));
+
+	spin_lock(&inode->i_lock);
+	cap = __get_cap_for_mds(ci, mds);
+	if (cap && __cap_is_valid(cap)) {
+		if (force ||
+		    ((cap->issued & drop) &&
+		     (cap->issued & unless) == 0)) {
+			if ((cap->issued & drop) &&
+			    (cap->issued & unless) == 0) {
+				dout("encode_inode_release %p cap %p %s -> "
+				     "%s\n", inode, cap,
+				     ceph_cap_string(cap->issued),
+				     ceph_cap_string(cap->issued & ~drop));
+				cap->issued &= ~drop;
+				cap->implemented &= ~drop;
+				if (ci->i_ceph_flags & CEPH_I_NODELAY) {
+					int wanted = __ceph_caps_wanted(ci);
+					dout("  wanted %s -> %s (act %s)\n",
+					     ceph_cap_string(cap->mds_wanted),
+					     ceph_cap_string(cap->mds_wanted &
+							     ~wanted),
+					     ceph_cap_string(wanted));
+					cap->mds_wanted &= wanted;
+				}
+			} else {
+				dout("encode_inode_release %p cap %p %s"
+				     " (force)\n", inode, cap,
+				     ceph_cap_string(cap->issued));
+			}
+
+			rel->ino = cpu_to_le64(ceph_ino(inode));
+			rel->cap_id = cpu_to_le64(cap->cap_id);
+			rel->seq = cpu_to_le32(cap->seq);
+			rel->issue_seq = cpu_to_le32(cap->issue_seq),
+			rel->mseq = cpu_to_le32(cap->mseq);
+			rel->caps = cpu_to_le32(cap->issued);
+			rel->wanted = cpu_to_le32(cap->mds_wanted);
+			rel->dname_len = 0;
+			rel->dname_seq = 0;
+			*p += sizeof(*rel);
+			ret = 1;
+		} else {
+			dout("encode_inode_release %p cap %p %s\n",
+			     inode, cap, ceph_cap_string(cap->issued));
+		}
+	}
+	spin_unlock(&inode->i_lock);
+	return ret;
+}
+
+int ceph_encode_dentry_release(void **p, struct dentry *dentry,
+			       int mds, int drop, int unless)
+{
+	struct inode *dir = dentry->d_parent->d_inode;
+	struct ceph_mds_request_release *rel = *p;
+	struct ceph_dentry_info *di = ceph_dentry(dentry);
+	int force = 0;
+	int ret;
+
+	/*
+	 * force an record for the directory caps if we have a dentry lease.
+	 * this is racy (can't take i_lock and d_lock together), but it
+	 * doesn't have to be perfect; the mds will revoke anything we don't
+	 * release.
+	 */
+	spin_lock(&dentry->d_lock);
+	if (di->lease_session && di->lease_session->s_mds == mds)
+		force = 1;
+	spin_unlock(&dentry->d_lock);
+
+	ret = ceph_encode_inode_release(p, dir, mds, drop, unless, force);
+
+	spin_lock(&dentry->d_lock);
+	if (ret && di->lease_session && di->lease_session->s_mds == mds) {
+		dout("encode_dentry_release %p mds%d seq %d\n",
+		     dentry, mds, (int)di->lease_seq);
+		rel->dname_len = cpu_to_le32(dentry->d_name.len);
+		memcpy(*p, dentry->d_name.name, dentry->d_name.len);
+		*p += dentry->d_name.len;
+		rel->dname_seq = cpu_to_le32(di->lease_seq);
+	}
+	spin_unlock(&dentry->d_lock);
+	return ret;
+}