[lkml]   [2009]   [Dec]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    Subjectutimensat fails to update ctime
    POSIX requires that utimensat/futimens must update ctime in all cases
    where any change is made (it only exempts when both atime and mtime were
    requested as UTIME_OMIT, where the file must exist but no change is made).
    Unfortunately, when atime is specified and mtime is UTIME_OMIT, the
    kernel mistakenly behaves like read(), by updating atime but not ctime.
    This in turn caused a regression in coreutils 8.2, visible through 'touch -a':

    Here is a simple program demonstrating the failure:
    $ cat foo.c
    #include <fcntl.h>
    #include <unistd.h>
    #include <sys/stat.h>
    main ()
    int fd = creat ("file", 0600);
    struct stat st1, st2;
    struct timespec t[2] = { { 1000000000, 0 }, { 0, UTIME_OMIT } };
    fstat (fd, &st1);
    sleep (1);
    futimens (fd, t);
    fstat (fd, &st2);
    return st1.st_ctime == st2.st_ctime;
    $ gcc -o foo foo.c -D_GNU_SOURCE
    $ ./foo; echo $?

    The exit status should have been 0.

    GNU coreutils will end up working around the bug by calling fstat/[l]stat
    prior to futimens/utimensat, and populating the mtime field with the
    desired value rather than using UTIME_OMIT. But this is a pointless stat
    call, which could be avoided if the kernel were fixed to comply with POSIX
    by updating ctime even when mtime is UTIME_OMIT.

    Don't work too hard, make some time for fun as well!

    Eric Blake

     \ /
      Last update: 2009-12-18 06:41    [W:0.018 / U:6.492 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site