[PATCH 0/6] Backport statx(..., NULL, AT_EMPTY_PATH, ...)

[Miao Wang via B4 Relay <devnull+shankerwangmiao.gmail.com@kernel.org>]

Commit 0ef625bba6fb ("vfs: support statx(..., NULL, AT_EMPTY_PATH,
...)") added support for passing in NULL when AT_EMPTY_PATH is given,
improving performance when statx is used for fetching stat informantion
from a given fd, which is especially important for 32-bit platforms.
This commit also improved the performance when an empty string is given
by short-circuiting the handling of such paths.

This series is based on the commits in the Linus’ tree. Comparing to the
original patches, the helper vfs_empty_path() is moved to stat.c from
linux/fs.h, because get_user() is only available in fs.h since v5.7,
where commit 80fbaf1c3f29 ('rcuwait: Add @State argument to
rcuwait_wait_event()') added linux/sched/signal.h to rcuwait.h, and
uaccess.h finally got its way to fs.h along the path uaccess.h -> 
sched/task.h -> sched/signal.h -> rcuwait.h -> percpu-rwsem.h -> fs.h.
uaccess.h cannot be directly included in fs.h before v5.7, where commit
df23e2be3d24 ('acpi: Remove header dependency') removed proc_fs.h from
acpi/acpi_bus.h, preventing arch/x86/boot/compressed/cmdline.c from
indirectly including fs.h. Otherwise, the function set_fs() defined in
asm/uaccess.h will get into cmdline.c, which contains another set_fs(),
resulting conflicting function definations. There is no users of
vfs_empty_path() except stat.c, and as a result, putting it in stat.c is
acceptable.

The existing vfs_statx_fd(), which is removed since v5.10, is utilized
to implement short-circuit handling of NULL and "" paths, instead of
introducing vfs_statx_path(), simplifying the implementation.

Tested-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Miao Wang <shankerwangmiao@gmail.com>
---
Christian Brauner (2):
      fs: new helper vfs_empty_path()
      stat: use vfs_empty_path() helper

Christoph Hellwig (2):
      fs: implement vfs_stat and vfs_lstat in terms of vfs_fstatat
      fs: move vfs_fstatat out of line

Linus Torvalds (1):
      vfs: mostly undo glibc turning 'fstat()' into 'fstatat(AT_EMPTY_PATH)'

Mateusz Guzik (1):
      vfs: support statx(..., NULL, AT_EMPTY_PATH, ...)

 fs/stat.c          | 58 +++++++++++++++++++++++++++++++++++++++++++++++++-----
 include/linux/fs.h | 26 ++++++++++--------------
 2 files changed, 63 insertions(+), 21 deletions(-)
---
base-commit: 661f109c057497c8baf507a2562ceb9f9fb3cbc2
change-id: 20240918-statx-stable-linux-5-4-y-a79d4268600d

Best regards,
-- 
Miao Wang <shankerwangmiao@gmail.com>