linux/fs/sysfs
KOSAKI Motohiro 1af3557abd sysfs: sysfs poll keep the poll rule of regular file.
Currently, following test programs don't finished.

% ruby -e '
Thread.new { sleep }
File.read("/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies")
'

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
http://www.opengroup.org/onlinepubs/009695399/functions/poll.html it
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: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-04-16 16:17:09 -07:00
..
bin.c mm: page_mkwrite change prototype to match fault: fix sysfs 2009-04-01 08:59:14 -07:00
dir.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6 2009-03-27 16:23:12 -07:00
file.c sysfs: sysfs poll keep the poll rule of regular file. 2009-04-16 16:17:09 -07:00
group.c Use WARN() in fs/sysfs 2008-07-26 12:00:07 -07:00
inode.c sysfs: reference sysfs_dirent from sysfs inodes 2009-03-24 16:38:25 -07:00
Kconfig fs/Kconfig: move sysfs out 2009-01-22 13:15:56 +03:00
Makefile
mount.c sysfs: reference sysfs_dirent from sysfs inodes 2009-03-24 16:38:25 -07:00
symlink.c driver core: Suppress sysfs warnings for device_rename(). 2008-07-21 21:55:01 -07:00
sysfs.h sysfs: don't block indefinitely for unmapped files. 2009-03-24 16:38:26 -07:00