Re: [PATCH 2/2] vfs: Make sure {statx,fstatat}(..., AT_EMPTY_PATH | ..., NULL, ...) behave as (..., AT_EMPTY_PATH | ..., "", ...)

On Mon, Oct 7, 2024 at 3:08 PM Xi Ruoyao xry111@xry111.site wrote:

We've supported {statx,fstatat}(real_fd, NULL, AT_EMPTY_PATH, ...) since Linux 6.11 for better performance. However there are other cases, for example using AT_FDCWD as the fd or having AT_SYMLINK_NOFOLLOW in flags, not covered by the fast path. While it may be impossible, too difficult, or not very beneficial to optimize these cases, we should still turn NULL into "" for them in the slow path to make the API easier to be documented and used.

Fixes: 0ef625bba6fb ("vfs: support statx(..., NULL, AT_EMPTY_PATH, ...)") Cc: stable@vger.kernel.org Signed-off-by: Xi Ruoyao xry111@xry111.site

---

fs/stat.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/stat.c b/fs/stat.c index ed9d4fd8ba2c..5d1b51c23c62 100644 --- a/fs/stat.c +++ b/fs/stat.c @@ -337,8 +337,11 @@ int vfs_fstatat(int dfd, const char __user *filename, flags &= ~AT_NO_AUTOMOUNT; if (flags == AT_EMPTY_PATH && vfs_empty_path(dfd, filename)) return vfs_fstat(dfd, stat);

•   else if ((flags & AT_EMPTY_PATH) && !filename)
  

•           name = getname_kernel("");
  

•   else
  

•           name = getname_flags(filename, getname_statx_lookup_flags(statx_flags));
  
  

•   name = getname_flags(filename, getname_statx_lookup_flags(statx_flags));
    ret = vfs_statx(dfd, name, statx_flags, stat, STATX_BASIC_STATS);
    putname(name);
  
  

@@ -791,8 +794,11 @@ SYSCALL_DEFINE5(statx, lflags = flags & ~(AT_NO_AUTOMOUNT | AT_STATX_SYNC_TYPE); if (lflags == AT_EMPTY_PATH && vfs_empty_path(dfd, filename)) return do_statx_fd(dfd, flags & ~AT_NO_AUTOMOUNT, mask, buffer);

•   else if ((lflags & AT_EMPTY_PATH) && !filename)
  

•           name = getname_kernel("");
  

•   else
  

•           name = getname_flags(filename, getname_statx_lookup_flags(flags));
  
  

•   name = getname_flags(filename, getname_statx_lookup_flags(flags));
    ret = do_statx(dfd, name, flags, mask, buffer);
    putname(name);
  
  

I thought you are going to patch up the 2 callsites of vfs_empty_path() or add the flags argument to said routine so that it can do the branching internally.

Either way I don't think implementing AT_FDCWD + NULL + AT_EMPTY_PATH with getname_kernel("") is necessary.