• KOSAKI Motohiro's avatar
    sysfs: sysfs poll keep the poll rule of regular file. · 1af3557a
    KOSAKI Motohiro authored
    Currently, following test programs don't finished.
    % ruby -e '
    Thread.new { sleep }
    strace expose the reason.
    open("/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies", O_RDONLY|O_LARGEFILE) = 3
    ioctl(3, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbf9fa6b8) = -1 ENOTTY (Inappropriate ioctl for device)
    fstat64(3, {st_mode=S_IFREG|0444, st_size=4096, ...}) = 0
    _llseek(3, 0, [0], SEEK_CUR)            = 0
    select(4, [3], NULL, NULL, NULL)        = 1 (in [3])
    read(3, "1400000 1300000 1200000 1100000 1"..., 4096) = 62
    select(4, [3], NULL, NULL, NULL
    Because Ruby (the scripting language) VM assume select system-call
    against regular file don't block.  it because SUSv3 says "Regular files
    shall always poll TRUE for reading and writing".  see
    seems valid assumption.
    But sysfs_poll() don't keep this rule although sysfs file can read and
    write always.
    This patch restore proper poll behavior to sysfs.
    /sys/block/md*/md/sync_action polling application and another sysfs
    updating sensitive application still can use POLLERR and POLLPRI.
    Cc: Neil Brown <neilb@suse.de>
    Signed-off-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>