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| author | Al Viro <viro@zeniv.linux.org.uk> | 2016-04-15 22:08:36 +0300 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2016-05-03 02:49:28 +0300 |
| commit | 9902af79c01a8e39bb99b922fa3eef6d4ea23d69 (patch) | |
| tree | b04cc75b5e4a028bfdb619e0a0a0f8cd71113ff2 /Documentation/filesystems/porting | |
| parent | d9171b9345261e0d941d92fdda5672b5db67f968 (diff) | |
| download | linux-9902af79c01a8e39bb99b922fa3eef6d4ea23d69.tar.xz | |
parallel lookups: actual switch to rwsem
ta-da!
The main issue is the lack of down_write_killable(), so the places
like readdir.c switched to plain inode_lock(); once killable
variants of rwsem primitives appear, that'll be dealt with.
lockdep side also might need more work
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'Documentation/filesystems/porting')
| -rw-r--r-- | Documentation/filesystems/porting | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting index 8810e2367fe6..1567a53857bd 100644 --- a/Documentation/filesystems/porting +++ b/Documentation/filesystems/porting @@ -539,3 +539,21 @@ in your dentry operations instead. it's a symlink. Checking ->i_mode is really needed now. In-tree we had to fix shmem_destroy_callback() that used to take that kind of shortcut; watch out, since that shortcut is no longer valid. +-- +[mandatory] + ->i_mutex is replaced with ->i_rwsem now. inode_lock() et.al. work as + they used to - they just take it exclusive. However, ->lookup() may be + called with parent locked shared. Its instances must not + * use d_instantiate) and d_rehash() separately - use d_add() or + d_splice_alias() instead. + * use d_rehash() alone - call d_add(new_dentry, NULL) instead. + * in the unlikely case when (read-only) access to filesystem + data structures needs exclusion for some reason, arrange it + yourself. None of the in-tree filesystems needed that. + * rely on ->d_parent and ->d_name not changing after dentry has + been fed to d_add() or d_splice_alias(). Again, none of the + in-tree instances relied upon that. + We are guaranteed that lookups of the same name in the same directory + will not happen in parallel ("same" in the sense of your ->d_compare()). + Lookups on different names in the same directory can and do happen in + parallel now. |