path: root/Documentation/filesystems
diff options
authorEric Biggers <>2020-09-22 09:44:18 -0700
committerAl Viro <>2021-01-04 14:02:08 -0500
commit14e43bf435612639cab01541fce7cc41bf7e370b (patch)
treed0a418ace1f97fbdc4ad4fcf88ce5119237bccdd /Documentation/filesystems
parent5c8fe583cce542aa0b84adc939ce85293de36e5e (diff)
vfs: don't unnecessarily clone write access for writable fds
There's no need for mnt_want_write_file() to increment mnt_writers when the file is already open for writing, provided that mnt_drop_write_file() is changed to conditionally decrement it. We seem to have ended up in the current situation because mnt_want_write_file() used to be paired with mnt_drop_write(), due to mnt_drop_write_file() not having been added yet. So originally mnt_want_write_file() had to always increment mnt_writers. But later mnt_drop_write_file() was added, and all callers of mnt_want_write_file() were paired with it. This makes the compatibility between mnt_want_write_file() and mnt_drop_write() no longer necessary. Therefore, make __mnt_want_write_file() and __mnt_drop_write_file() skip incrementing mnt_writers on files already open for writing. This removes the only caller of mnt_clone_write(), so remove that too. Signed-off-by: Eric Biggers <> Signed-off-by: Al Viro <>
Diffstat (limited to 'Documentation/filesystems')
1 files changed, 7 insertions, 0 deletions
diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst
index 867036aa90b8..6a6d3e673b48 100644
--- a/Documentation/filesystems/porting.rst
+++ b/Documentation/filesystems/porting.rst
@@ -865,3 +865,10 @@ no matter what. Everything is handled by the caller.
clone_private_mount() returns a longterm mount now, so the proper destructor of
its result is kern_unmount() or kern_unmount_array().
+mnt_want_write_file() can now only be paired with mnt_drop_write_file(),
+whereas previously it could be paired with mnt_drop_write() as well.