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author | Nick Piggin <npiggin@kernel.dk> | 2011-01-07 17:49:57 +1100 |
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committer | Nick Piggin <npiggin@kernel.dk> | 2011-01-07 17:50:29 +1100 |
commit | 34286d6662308d82aed891852d04c7c3a2649b16 (patch) | |
tree | c4b7311404d302e7cb94df7a4690298e1059910a /Documentation/filesystems/porting | |
parent | 44a7d7a878c9cbb74f236ea755b25b6b2e26a9a9 (diff) | |
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fs: rcu-walk aware d_revalidate method
Require filesystems be aware of .d_revalidate being called in rcu-walk
mode (nd->flags & LOOKUP_RCU). For now do a simple push down, returning
-ECHILD from all implementations.
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
Diffstat (limited to 'Documentation/filesystems/porting')
-rw-r--r-- | Documentation/filesystems/porting | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting index ccf0ce7..cd9756a 100644 --- a/Documentation/filesystems/porting +++ b/Documentation/filesystems/porting @@ -360,3 +360,23 @@ i_dentry to be reinitialized before it is freed, so an: INIT_LIST_HEAD(&inode->i_dentry); must be done in the RCU callback. + +-- +[recommended] + vfs now tries to do path walking in "rcu-walk mode", which avoids +atomic operations and scalability hazards on dentries and inodes (see +Documentation/filesystems/path-walk.txt). d_hash and d_compare changes (above) +are examples of the changes required to support this. For more complex +filesystem callbacks, the vfs drops out of rcu-walk mode before the fs call, so +no changes are required to the filesystem. However, this is costly and loses +the benefits of rcu-walk mode. We will begin to add filesystem callbacks that +are rcu-walk aware, shown below. Filesystems should take advantage of this +where possible. + +-- +[mandatory] + d_revalidate is a callback that is made on every path element (if +the filesystem provides it), which requires dropping out of rcu-walk mode. This +may now be called in rcu-walk mode (nd->flags & LOOKUP_RCU). -ECHILD should be +returned if the filesystem cannot handle rcu-walk. See +Documentation/filesystems/vfs.txt for more details. |