Probably not for this merge window anymore but let me get it out now:
The f_version member in struct file isn't particularly well-defined. It
is mainly used as a cookie to detect concurrent seeks when iterating
directories. But it is also abused by some subsystems for completely
unrelated things.
It is mostly a directory specific thing that doesn't really need to live
in struct file and with its wonky semantics it really lacks a specific
function.
For pipes, f_version is (ab)used to defer poll notifications until a
write has happened. And struct pipe_inode_info is used by multiple
struct files in their ->private_data so there's no chance of pushing
that down into file->private_data without introducing another pointer
indirection.
But this should be a solvable problem. Only regular files with
FMODE_ATOMIC_POS and directories require f_pos_lock. Pipes and other
files don't. So this adds a union into struct file encompassing
f_pos_lock and a pipe specific f_pipe member that pipes can use. This
union of course can be extended to other file types and is similar to
what we do in struct inode already.
I hope I got the details right. It at least holds up in xfstests and LTP
and my hand-rolled getdents-seek stressor.
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
---
Christian Brauner (20):
file: remove pointless comment
adi: remove unused f_version
ceph: remove unused f_version
s390: remove unused f_version
fs: add vfs_setpos_cookie()
fs: add must_set_pos()
fs: use must_set_pos()
fs: add generic_llseek_cookie()
affs: store cookie in private data
ext2: store cookie in private data
ext4: store cookie in private data
input: remove f_version abuse
ocfs2: store cookie in private data
proc: store cookie in private data
udf: store cookie in private data
ufs: store cookie in private data
ubifs: store cookie in private data
fs: add f_pipe
pipe: use f_pipe
fs: remove f_version
drivers/char/adi.c | 1 -
drivers/input/input.c | 8 +-
drivers/s390/char/hmcdrv_dev.c | 3 -
fs/affs/dir.c | 44 +++++++++--
fs/ceph/dir.c | 1 -
fs/ext2/dir.c | 28 ++++++-
fs/ext4/dir.c | 50 ++++++------
fs/ext4/ext4.h | 2 +
fs/ext4/inline.c | 7 +-
fs/file_table.c | 1 -
fs/ocfs2/dir.c | 3 +-
fs/ocfs2/file.c | 11 ++-
fs/ocfs2/file.h | 1 +
fs/pipe.c | 6 +-
fs/proc/base.c | 18 +++--
fs/read_write.c | 169 +++++++++++++++++++++++++++++++----------
fs/ubifs/dir.c | 65 +++++++++++-----
fs/udf/dir.c | 28 ++++++-
fs/ufs/dir.c | 28 ++++++-
include/linux/fs.h | 14 +++-
20 files changed, 366 insertions(+), 122 deletions(-)
---
base-commit: 79868ff5ce9156228f9aef351d8bf76fb8540230
change-id: 20240829-vfs-file-f_version-66321e3dafeb
