• Ulrich Drepper's avatar
    [PATCH] vfs: *at functions: core · 5590ff0d
    Ulrich Drepper authored
    Here is a series of patches which introduce in total 13 new system calls
    which take a file descriptor/filename pair instead of a single file
    name.  These functions, openat etc, have been discussed on numerous
    occasions.  They are needed to implement race-free filesystem traversal,
    they are necessary to implement a virtual per-thread current working
    directory (think multi-threaded backup software), etc.
    We have in glibc today implementations of the interfaces which use the
    /proc/self/fd magic.  But this code is rather expensive.  Here are some
    results (similar to what Jim Meyering posted before).
    The test creates a deep directory hierarchy on a tmpfs filesystem.  Then
    rm -fr is used to remove all directories.  Without syscall support I get
    real    0m31.921s
    user    0m0.688s
    sys     0m31.234s
    With syscall support the results are much better:
    real    0m20.699s
    user    0m0.536s
    sys     0m20.149s
    The interfaces are for obvious reasons currently not much used.  But they'll
    be used.  coreutils (and Jeff's posixutils) are already using them.
    Furthermore, code like ftw/fts in libc (maybe even glob) will also start using
    them.  I expect a patch to make follow soon.  Every program which is walking
    the filesystem tree will benefit.
    Signed-off-by: default avatarUlrich Drepper <drepper@redhat.com>
    Signed-off-by: default avatarAlexey Dobriyan <adobriyan@gmail.com>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Al Viro <viro@ftp.linux.org.uk>
    Acked-by: default avatarIngo Molnar <mingo@elte.hu>
    Cc: Michael Kerrisk <mtk-manpages@gmx.net>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
open.c 26.8 KB