From ecf3d1f1aa74da0d632b651a2e05a911f60e92c0 Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Wed, 20 Feb 2013 11:19:05 -0500 Subject: vfs: kill FS_REVAL_DOT by adding a d_weak_revalidate dentry op The following set of operations on a NFS client and server will cause server# mkdir a client# cd a server# mv a a.bak client# sleep 30 # (or whatever the dir attrcache timeout is) client# stat . stat: cannot stat `.': Stale NFS file handle Obviously, we should not be getting an ESTALE error back there since the inode still exists on the server. The problem is that the lookup code will call d_revalidate on the dentry that "." refers to, because NFS has FS_REVAL_DOT set. nfs_lookup_revalidate will see that the parent directory has changed and will try to reverify the dentry by redoing a LOOKUP. That of course fails, so the lookup code returns ESTALE. The problem here is that d_revalidate is really a bad fit for this case. What we really want to know at this point is whether the inode is still good or not, but we don't really care what name it goes by or whether the dcache is still valid. Add a new d_op->d_weak_revalidate operation and have complete_walk call that instead of d_revalidate. The intent there is to allow for a "weaker" d_revalidate that just checks to see whether the inode is still good. This is also gives us an opportunity to kill off the FS_REVAL_DOT special casing. [AV: changed method name, added note in porting, fixed confusion re having it possibly called from RCU mode (it won't be)] Cc: NeilBrown Signed-off-by: Jeff Layton Signed-off-by: Al Viro --- Documentation/filesystems/Locking | 2 ++ Documentation/filesystems/porting | 4 ++++ Documentation/filesystems/vfs.txt | 24 ++++++++++++++++++++++-- 3 files changed, 28 insertions(+), 2 deletions(-) (limited to 'Documentation') diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking index f48e0c6b4c4..0706d32a61e 100644 --- a/Documentation/filesystems/Locking +++ b/Documentation/filesystems/Locking @@ -10,6 +10,7 @@ be able to use diff(1). --------------------------- dentry_operations -------------------------- prototypes: int (*d_revalidate)(struct dentry *, unsigned int); + int (*d_weak_revalidate)(struct dentry *, unsigned int); int (*d_hash)(const struct dentry *, const struct inode *, struct qstr *); int (*d_compare)(const struct dentry *, const struct inode *, @@ -25,6 +26,7 @@ prototypes: locking rules: rename_lock ->d_lock may block rcu-walk d_revalidate: no no yes (ref-walk) maybe +d_weak_revalidate:no no yes no d_hash no no no maybe d_compare: yes no no maybe d_delete: no yes no no diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting index 0472c31c163..4db22f6491e 100644 --- a/Documentation/filesystems/porting +++ b/Documentation/filesystems/porting @@ -441,3 +441,7 @@ d_make_root() drops the reference to inode if dentry allocation fails. two, it gets "is it an O_EXCL or equivalent?" boolean argument. Note that local filesystems can ignore tha argument - they are guaranteed that the object doesn't exist. It's remote/distributed ones that might care... +-- +[mandatory] + FS_REVAL_DOT is gone; if you used to have it, add ->d_weak_revalidate() +in your dentry operations instead. diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index e3869098163..bc4b06b3160 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -900,6 +900,7 @@ defined: struct dentry_operations { int (*d_revalidate)(struct dentry *, unsigned int); + int (*d_weak_revalidate)(struct dentry *, unsigned int); int (*d_hash)(const struct dentry *, const struct inode *, struct qstr *); int (*d_compare)(const struct dentry *, const struct inode *, @@ -915,8 +916,13 @@ struct dentry_operations { d_revalidate: called when the VFS needs to revalidate a dentry. This is called whenever a name look-up finds a dentry in the - dcache. Most filesystems leave this as NULL, because all their - dentries in the dcache are valid + dcache. Most local filesystems leave this as NULL, because all their + dentries in the dcache are valid. Network filesystems are different + since things can change on the server without the client necessarily + being aware of it. + + This function should return a positive value if the dentry is still + valid, and zero or a negative error code if it isn't. d_revalidate may be called in rcu-walk mode (flags & LOOKUP_RCU). If in rcu-walk mode, the filesystem must revalidate the dentry without @@ -927,6 +933,20 @@ struct dentry_operations { If a situation is encountered that rcu-walk cannot handle, return -ECHILD and it will be called again in ref-walk mode. + d_weak_revalidate: called when the VFS needs to revalidate a "jumped" dentry. + This is called when a path-walk ends at dentry that was not acquired by + doing a lookup in the parent directory. This includes "/", "." and "..", + as well as procfs-style symlinks and mountpoint traversal. + + In this case, we are less concerned with whether the dentry is still + fully correct, but rather that the inode is still valid. As with + d_revalidate, most local filesystems will set this to NULL since their + dcache entries are always valid. + + This function has the same return code semantics as d_revalidate. + + d_weak_revalidate is only called after leaving rcu-walk mode. + d_hash: called when the VFS adds a dentry to the hash table. The first dentry passed to d_hash is the parent directory that the name is to be hashed into. The inode is the dentry's inode. -- cgit v1.2.3-70-g09d2