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authorDavid Chinner <dgc@sgi.com>2008-04-29 12:53:32 +1000
committerLachlan McIlroy <lachlan@redback.melbourne.sgi.com>2008-04-29 15:58:56 +1000
commit359346a9655c8800408ed3ca44517ac7ea95c197 (patch)
tree4a97c2956dc5204fd28c26008bbf1f27c1e684bf
parent86c4d62305649848164ae311a0959fc569b0d964 (diff)
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[XFS] Don't initialise new inode generation numbers to zero
When we allocation new inode chunks, we initialise the generation numbers to zero. This works fine until we delete a chunk and then reallocate it, resulting in the same inode numbers but with a reset generation count. This can result in inode/generation pairs of different inodes occurring relatively close together. Given that the inode/gen pair makes up the "unique" portion of an NFS filehandle on XFS, this can result in file handles cached on clients being seen on the wire from the server but refer to a different file. This causes .... issues for NFS clients. Hence we need a unique generation number initialisation for each inode to prevent reuse of a small portion of the generation number space. Use a random number to initialise the generation number so we don't need to keep any new state on disk whilst making the new number difficult to guess from previous allocations. SGI-PV: 979416 SGI-Modid: xfs-linux-melb:xfs-kern:31001a Signed-off-by: David Chinner <dgc@sgi.com> Signed-off-by: Christoph Hellwig <hch@infradead.org> Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
-rw-r--r--fs/xfs/xfs_ialloc.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/fs/xfs/xfs_ialloc.c b/fs/xfs/xfs_ialloc.c
index a64dfbd..aad8c5d 100644
--- a/fs/xfs/xfs_ialloc.c
+++ b/fs/xfs/xfs_ialloc.c
@@ -147,6 +147,7 @@ xfs_ialloc_ag_alloc(
int version; /* inode version number to use */
int isaligned = 0; /* inode allocation at stripe unit */
/* boundary */
+ unsigned int gen;
args.tp = tp;
args.mp = tp->t_mountp;
@@ -290,6 +291,14 @@ xfs_ialloc_ag_alloc(
else
version = XFS_DINODE_VERSION_1;
+ /*
+ * Seed the new inode cluster with a random generation number. This
+ * prevents short-term reuse of generation numbers if a chunk is
+ * freed and then immediately reallocated. We use random numbers
+ * rather than a linear progression to prevent the next generation
+ * number from being easily guessable.
+ */
+ gen = random32();
for (j = 0; j < nbufs; j++) {
/*
* Get the block.
@@ -309,6 +318,7 @@ xfs_ialloc_ag_alloc(
free = XFS_MAKE_IPTR(args.mp, fbuf, i);
free->di_core.di_magic = cpu_to_be16(XFS_DINODE_MAGIC);
free->di_core.di_version = version;
+ free->di_core.di_gen = cpu_to_be32(gen);
free->di_next_unlinked = cpu_to_be32(NULLAGINO);
xfs_ialloc_log_di(tp, fbuf, i,
XFS_DI_CORE_BITS | XFS_DI_NEXT_UNLINKED);