[lkml]   [2001]   [Nov]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: File System Performance
    Linus Torvalds wrote:
    > On Mon, 12 Nov 2001, Lionel Bouton wrote:
    > >
    > > Seems not the case with gnu tar : write isn't even called once on the fd
    > > returned by open("/dev/null",...). In fact a "grep write" on the strace
    > > output is empty in the "tar cf /dev/null" case. Every file in the tar-ed
    > > tree is stat-ed but no-one is read-ed.
    > Wow. What a sleazy optimization - it can't be anything but a special case.
    > How do they do it anyway? By matching on the name Or by knowing what the
    > minor/major numbers of /dev/null are supposed to be on that particular
    > operating system?

    /* Detect if outputting to "/dev/null". */
    static char const dev_null[] = "/dev/null";
    struct stat dev_null_stat;

    dev_null_output =
    (strcmp (archive_name_array[0], dev_null) == 0
    || (! _isrmt (archive)
    && stat (dev_null, &dev_null_stat) == 0
    && S_ISCHR (archive_stat.st_mode)
    && archive_stat.st_rdev == dev_null_stat.st_rdev));

    > And what's the _point_ of the optimization? I've never heard of a "tar
    > benchmark"..

    Ask Al. He understands those GNU folks.

    It's actually a bug. I may _want_ an ISREG /dev/null...

    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2005-03-22 13:13    [W:0.024 / U:68.020 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site