[XFS] Return case-insensitive match for dentry cache

This implements the code to store the actual filename found during a
lookup in the dentry cache and to avoid multiple entries in the dcache
pointing to the same inode.

To avoid polluting the dcache, we implement a new directory inode
operations for lookup. xfs_vn_ci_lookup() stores the correct case name in
the dcache.

The "actual name" is only allocated and returned for a case- insensitive
match and not an actual match.

Another unusual interaction with the dcache is not storing negative
dentries like other filesystems doing a d_add(dentry, NULL) when an ENOENT
is returned. During the VFS lookup, if a dentry returned has no inode,
dput is called and ENOENT is returned. By not doing a d_add, this actually
removes it completely from the dcache to be reused. create/rename have to
be modified to support unhashed dentries being passed in.

SGI-PV: 981521
SGI-Modid: xfs-linux-melb:xfs-kern:31208a

Signed-off-by: Barry Naujok <bnaujok@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>

1 files changed, 14 insertions, 5 deletions

diff --git a/fs/xfs/xfs_vnodeops.c b/fs/xfs/xfs_vnodeops.c
index 9b8b87fcd4e..b6a065eb25a 100644
--- a/fs/xfs/xfs_vnodeops.c
+++ b/fs/xfs/xfs_vnodeops.c
@@ -1610,12 +1610,18 @@ xfs_inactive(
 	return VN_INACTIVE_CACHE;
 }
 
-
+/*
+ * Lookups up an inode from "name". If ci_name is not NULL, then a CI match
+ * is allowed, otherwise it has to be an exact match. If a CI match is found,
+ * ci_name->name will point to a the actual name (caller must free) or
+ * will be set to NULL if an exact match is found.
+ */
 int
 xfs_lookup(
 	xfs_inode_t		*dp,
 	struct xfs_name		*name,
-	xfs_inode_t		**ipp)
+	xfs_inode_t		**ipp,
+	struct xfs_name		*ci_name)
 {
 	xfs_ino_t		inum;
 	int			error;
@@ -1627,7 +1633,7 @@ xfs_lookup(
 		return XFS_ERROR(EIO);
 
 	lock_mode = xfs_ilock_map_shared(dp);
-	error = xfs_dir_lookup(NULL, dp, name, &inum);
+	error = xfs_dir_lookup(NULL, dp, name, &inum, ci_name);
 	xfs_iunlock_map_shared(dp, lock_mode);
 
 	if (error)
@@ -1635,12 +1641,15 @@ xfs_lookup(
 
 	error = xfs_iget(dp->i_mount, NULL, inum, 0, 0, ipp, 0);
 	if (error)
-		goto out;
+		goto out_free_name;
 
 	xfs_itrace_ref(*ipp);
 	return 0;
 
- out:
+out_free_name:
+	if (ci_name)
+		kmem_free(ci_name->name);
+out:
 	*ipp = NULL;
 	return error;
 }