libfs: allow error return from simple attributes

Sometimes simple attributes might need to return an error, e.g. for
acquiring a mutex interruptibly.  In fact we have that situation in
spufs already which is the original user of the simple attributes.  This
patch merged the temporarily forked attributes in spufs back into the
main ones and allows to return errors.

[akpm@linux-foundation.org: build fix]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: <stefano.brivio@polimi.it>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg KH <greg@kroah.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

7 files changed, 69 insertions, 47 deletions

diff --git a/arch/avr32/kernel/ocd.c b/arch/avr32/kernel/ocd.c
index c4f0232..1b0245d 100644
--- a/arch/avr32/kernel/ocd.c
+++ b/arch/avr32/kernel/ocd.c
@@ -90,25 +90,29 @@ static struct dentry *ocd_debugfs_DC;
 static struct dentry *ocd_debugfs_DS;
 static struct dentry *ocd_debugfs_count;
 
-static u64 ocd_DC_get(void *data)
+static int ocd_DC_get(void *data, u64 *val)
 {
-	return ocd_read(DC);
+	*val = ocd_read(DC);
+	return 0;
 }
-static void ocd_DC_set(void *data, u64 val)
+static int ocd_DC_set(void *data, u64 val)
 {
 	ocd_write(DC, val);
+	return 0;
 }
 DEFINE_SIMPLE_ATTRIBUTE(fops_DC, ocd_DC_get, ocd_DC_set, "0x%08llx\n");
 
-static u64 ocd_DS_get(void *data)
+static int ocd_DS_get(void *data, u64 *val)
 {
-	return ocd_read(DS);
+	*val = ocd_read(DS);
+	return 0;
 }
 DEFINE_SIMPLE_ATTRIBUTE(fops_DS, ocd_DS_get, NULL, "0x%08llx\n");
 
-static u64 ocd_count_get(void *data)
+static int ocd_count_get(void *data, u64 *val)
 {
-	return ocd_count;
+	*val = ocd_count;
+	return 0;
 }
 DEFINE_SIMPLE_ATTRIBUTE(fops_count, ocd_count_get, NULL, "%lld\n");
 
diff --git a/arch/powerpc/platforms/cell/spufs/file.c b/arch/powerpc/platforms/cell/spufs/file.c
index 1018acd..9326714 100644
--- a/arch/powerpc/platforms/cell/spufs/file.c
+++ b/arch/powerpc/platforms/cell/spufs/file.c
@@ -460,7 +460,7 @@ static int spufs_cntl_open(struct inode *inode, struct file *file)
 	if (!i->i_openers++)
 		ctx->cntl = inode->i_mapping;
 	mutex_unlock(&ctx->mapping_lock);
-	return spufs_attr_open(inode, file, spufs_cntl_get,
+	return simple_attr_open(inode, file, spufs_cntl_get,
 					spufs_cntl_set, "0x%08lx");
 }
 
@@ -470,7 +470,7 @@ spufs_cntl_release(struct inode *inode, struct file *file)
 	struct spufs_inode_info *i = SPUFS_I(inode);
 	struct spu_context *ctx = i->i_ctx;
 
-	spufs_attr_release(inode, file);
+	simple_attr_close(inode, file);
 
 	mutex_lock(&ctx->mapping_lock);
 	if (!--i->i_openers)
@@ -482,8 +482,8 @@ spufs_cntl_release(struct inode *inode, struct file *file)
 static const struct file_operations spufs_cntl_fops = {
 	.open = spufs_cntl_open,
 	.release = spufs_cntl_release,
-	.read = spufs_attr_read,
-	.write = spufs_attr_write,
+	.read = simple_attr_read,
+	.write = simple_attr_write,
 	.mmap = spufs_cntl_mmap,
 };
 
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index fa6b7f7..fddffe4 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -56,13 +56,15 @@ const struct inode_operations debugfs_link_operations = {
 	.follow_link    = debugfs_follow_link,
 };
 
-static void debugfs_u8_set(void *data, u64 val)
+static int debugfs_u8_set(void *data, u64 val)
 {
 	*(u8 *)data = val;
+	return 0;
 }
-static u64 debugfs_u8_get(void *data)
+static int debugfs_u8_get(void *data, u64 *val)
 {
-	return *(u8 *)data;
+	*val = *(u8 *)data;
+	return 0;
 }
 DEFINE_SIMPLE_ATTRIBUTE(fops_u8, debugfs_u8_get, debugfs_u8_set, "%llu\n");
 
@@ -97,13 +99,15 @@ struct dentry *debugfs_create_u8(const char *name, mode_t mode,
 }
 EXPORT_SYMBOL_GPL(debugfs_create_u8);
 
-static void debugfs_u16_set(void *data, u64 val)
+static int debugfs_u16_set(void *data, u64 val)
 {
 	*(u16 *)data = val;
+	return 0;
 }
-static u64 debugfs_u16_get(void *data)
+static int debugfs_u16_get(void *data, u64 *val)
 {
-	return *(u16 *)data;
+	*val = *(u16 *)data;
+	return 0;
 }
 DEFINE_SIMPLE_ATTRIBUTE(fops_u16, debugfs_u16_get, debugfs_u16_set, "%llu\n");
 
@@ -138,13 +142,15 @@ struct dentry *debugfs_create_u16(const char *name, mode_t mode,
 }
 EXPORT_SYMBOL_GPL(debugfs_create_u16);
 
-static void debugfs_u32_set(void *data, u64 val)
+static int debugfs_u32_set(void *data, u64 val)
 {
 	*(u32 *)data = val;
+	return 0;
 }
-static u64 debugfs_u32_get(void *data)
+static int debugfs_u32_get(void *data, u64 *val)
 {
-	return *(u32 *)data;
+	*val = *(u32 *)data;
+	return 0;
 }
 DEFINE_SIMPLE_ATTRIBUTE(fops_u32, debugfs_u32_get, debugfs_u32_set, "%llu\n");
 
@@ -179,14 +185,16 @@ struct dentry *debugfs_create_u32(const char *name, mode_t mode,
 }
 EXPORT_SYMBOL_GPL(debugfs_create_u32);
 
-static void debugfs_u64_set(void *data, u64 val)
+static int debugfs_u64_set(void *data, u64 val)
 {
 	*(u64 *)data = val;
+	return 0;
 }
 
-static u64 debugfs_u64_get(void *data)
+static int debugfs_u64_get(void *data, u64 *val)
 {
-	return *(u64 *)data;
+	*val = *(u64 *)data;
+	return 0;
 }
 DEFINE_SIMPLE_ATTRIBUTE(fops_u64, debugfs_u64_get, debugfs_u64_set, "%llu\n");
 
diff --git a/fs/libfs.c b/fs/libfs.c
index 5523bde..2319415 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -583,8 +583,8 @@ int simple_transaction_release(struct inode *inode, struct file *file)
 /* Simple attribute files */
 
 struct simple_attr {
-	u64 (*get)(void *);
-	void (*set)(void *, u64);
+	int (*get)(void *, u64 *);
+	int (*set)(void *, u64);
 	char get_buf[24];	/* enough to store a u64 and "\n\0" */
 	char set_buf[24];
 	void *data;
@@ -595,7 +595,7 @@ struct simple_attr {
 /* simple_attr_open is called by an actual attribute open file operation
  * to set the attribute specific access operations. */
 int simple_attr_open(struct inode *inode, struct file *file,
-		     u64 (*get)(void *), void (*set)(void *, u64),
+		     int (*get)(void *, u64 *), int (*set)(void *, u64),
 		     const char *fmt)
 {
 	struct simple_attr *attr;
@@ -635,14 +635,20 @@ ssize_t simple_attr_read(struct file *file, char __user *buf,
 		return -EACCES;
 
 	mutex_lock(&attr->mutex);
-	if (*ppos) /* continued read */
+	if (*ppos) {		/* continued read */
 		size = strlen(attr->get_buf);
-	else	  /* first read */
+	} else {		/* first read */
+		u64 val;
+		ret = attr->get(attr->data, &val);
+		if (ret)
+			goto out;
+
 		size = scnprintf(attr->get_buf, sizeof(attr->get_buf),
-				 attr->fmt,
-				 (unsigned long long)attr->get(attr->data));
+				 attr->fmt, (unsigned long long)val);
+	}
 
 	ret = simple_read_from_buffer(buf, len, ppos, attr->get_buf, size);
+out:
 	mutex_unlock(&attr->mutex);
 	return ret;
 }
@@ -657,7 +663,6 @@ ssize_t simple_attr_write(struct file *file, const char __user *buf,
 	ssize_t ret;
 
 	attr = file->private_data;
-
 	if (!attr->set)
 		return -EACCES;
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 36b7abe..ebe996a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2068,7 +2068,7 @@ __simple_attr_check_format(const char *fmt, ...)
 }
 
 int simple_attr_open(struct inode *inode, struct file *file,
-		     u64 (*get)(void *), void (*set)(void *, u64),
+		     int (*get)(void *, u64 *), int (*set)(void *, u64),
 		     const char *fmt);
 int simple_attr_close(struct inode *inode, struct file *file);
 ssize_t simple_attr_read(struct file *file, char __user *buf,
diff --git a/lib/fault-inject.c b/lib/fault-inject.c
index 23985a2..a50a311 100644
--- a/lib/fault-inject.c
+++ b/lib/fault-inject.c
@@ -134,23 +134,26 @@ bool should_fail(struct fault_attr *attr, ssize_t size)
 
 #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
 
-static void debugfs_ul_set(void *data, u64 val)
+static int debugfs_ul_set(void *data, u64 val)
 {
 	*(unsigned long *)data = val;
+	return 0;
 }
 
 #ifdef CONFIG_FAULT_INJECTION_STACKTRACE_FILTER
-static void debugfs_ul_set_MAX_STACK_TRACE_DEPTH(void *data, u64 val)
+static int debugfs_ul_set_MAX_STACK_TRACE_DEPTH(void *data, u64 val)
 {
 	*(unsigned long *)data =
 		val < MAX_STACK_TRACE_DEPTH ?
 		val : MAX_STACK_TRACE_DEPTH;
+	return 0;
 }
 #endif /* CONFIG_FAULT_INJECTION_STACKTRACE_FILTER */
 
-static u64 debugfs_ul_get(void *data)
+static int debugfs_ul_get(void *data, u64 *val)
 {
-	return *(unsigned long *)data;
+	*val = *(unsigned long *)data;
+	return 0;
 }
 
 DEFINE_SIMPLE_ATTRIBUTE(fops_ul, debugfs_ul_get, debugfs_ul_set, "%llu\n");
@@ -174,14 +177,16 @@ static struct dentry *debugfs_create_ul_MAX_STACK_TRACE_DEPTH(
 }
 #endif /* CONFIG_FAULT_INJECTION_STACKTRACE_FILTER */
 
-static void debugfs_atomic_t_set(void *data, u64 val)
+static int debugfs_atomic_t_set(void *data, u64 val)
 {
 	atomic_set((atomic_t *)data, val);
+	return 0;
 }
 
-static u64 debugfs_atomic_t_get(void *data)
+static int debugfs_atomic_t_get(void *data, u64 *val)
 {
-	return atomic_read((atomic_t *)data);
+	*val = atomic_read((atomic_t *)data);
+	return 0;
 }
 
 DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t, debugfs_atomic_t_get,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3c4fe26..32fbf80 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1186,38 +1186,38 @@ static struct notifier_block kvm_cpu_notifier = {
 	.priority = 20, /* must be > scheduler priority */
 };
 
-static u64 vm_stat_get(void *_offset)
+static int vm_stat_get(void *_offset, u64 *val)
 {
 	unsigned offset = (long)_offset;
-	u64 total = 0;
 	struct kvm *kvm;
 
+	*val = 0;
 	spin_lock(&kvm_lock);
 	list_for_each_entry(kvm, &vm_list, vm_list)
-		total += *(u32 *)((void *)kvm + offset);
+		*val += *(u32 *)((void *)kvm + offset);
 	spin_unlock(&kvm_lock);
-	return total;
+	return 0;
 }
 
 DEFINE_SIMPLE_ATTRIBUTE(vm_stat_fops, vm_stat_get, NULL, "%llu\n");
 
-static u64 vcpu_stat_get(void *_offset)
+static int vcpu_stat_get(void *_offset, u64 *val)
 {
 	unsigned offset = (long)_offset;
-	u64 total = 0;
 	struct kvm *kvm;
 	struct kvm_vcpu *vcpu;
 	int i;
 
+	*val = 0;
 	spin_lock(&kvm_lock);
 	list_for_each_entry(kvm, &vm_list, vm_list)
 		for (i = 0; i < KVM_MAX_VCPUS; ++i) {
 			vcpu = kvm->vcpus[i];
 			if (vcpu)
-				total += *(u32 *)((void *)vcpu + offset);
+				*val += *(u32 *)((void *)vcpu + offset);
 		}
 	spin_unlock(&kvm_lock);
-	return total;
+	return 0;
 }
 
 DEFINE_SIMPLE_ATTRIBUTE(vcpu_stat_fops, vcpu_stat_get, NULL, "%llu\n");