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authorNick Piggin <npiggin@kernel.dk>2011-01-07 17:49:57 +1100
committerNick Piggin <npiggin@kernel.dk>2011-01-07 17:50:29 +1100
commit34286d6662308d82aed891852d04c7c3a2649b16 (patch)
treec4b7311404d302e7cb94df7a4690298e1059910a /Documentation/filesystems/porting
parent44a7d7a878c9cbb74f236ea755b25b6b2e26a9a9 (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')
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diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index ccf0ce7866b9..cd9756a2709d 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.