On Fri, Oct 18, 2024 at 12:54:59AM +0100, Al Viro wrote: > On Wed, Oct 16, 2024 at 04:49:48PM +0200, Christian Brauner wrote: > > On Wed, Oct 16, 2024 at 03:00:50PM +0100, Al Viro wrote: > > > On Wed, Oct 16, 2024 at 10:32:16AM +0200, Christian Brauner wrote: > > > > > > > > ended up calling user_path_at() with empty pathname and nothing like LOOKUP_EMPTY > > > > > in lookup_flags. Which bails out with -ENOENT, since getname() in there does > > > > > so. My variant bails out with -EBADF and I'd argue that neither is correct. > > > > > > > > > > Not sure what's the sane solution here, need to think for a while... > > > > > > > > Fwiw, in the other thread we concluded to just not care about AT_FDCWD with "". > > > > And so far I agree with that. > > > > > > Subject:? > > > > https://lore.kernel.org/r/CAGudoHHdccL5Lh8zAO-0swqqRCW4GXMSXhq4jQGoVj=UdBK-Lg@xxxxxxxxxxxxxx > > > > Hm, this only speaks about the NULL case. > > > > > > I just looked through codesearch on github and on debian and the only > > example I found was > > https://sources.debian.org/src/snapd/2.65.3-1/tests/main/seccomp-statx/test-snapd-statx/bin/statx.py/?hl=71#L71 > > > > So really, just special-case it for statx() imho instead of spreading > > that ugliness everywhere? > > Not sure, TBH. I wonder if it would be simpler to have filename_lookup() > accept NULL for pathname and have it treat that as "". > > Look: all it takes is the following trick > * add const char *pathname to struct nameidata > * in __set_nameidata() add > p->pathname = likely(name) ? name->name : ""; > * in path_init() replace > const char *s = nd->name->name; > with > const char *s = nd->pathname; > and we are done. Oh, and teach putname() to treat NULL as no-op. I know, that's what I suggested to Linus initially but he NAKed it because he didn't want the extra cycles. > > With such changes in fs/namei.c we could do > struct filename *name = getname_maybe_null(filename, flags); > > if (!name && dfd != AT_FDCWD) > return do_statx_fd(dfd, flags & ~AT_NO_AUTOMOUNT, mask, buffer); > ret = vfs_statx(dfd, name, statx_flags, stat, STATX_BASIC_STATS); > putname(name); > return ret; > in statx(2) and similar in vfs_fstatat(). > > With that I'm not even sure we want to bother with separate > vfs_statx_fd() - the overhead might very well turn out to > be tolerable. It is non-zero, but that's a fairly straight > trip through filename_lookup() machinery. Would require some > profiling, though...
