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| author | KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> | 2009-04-09 13:53:22 +0900 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2009-04-16 16:17:09 -0700 |
| commit | 1af3557abdef34ee036a6de4cb79e24468544b8d (patch) | |
| tree | f390d8d72bbba5302fcafb4c3666ac92469b488a | |
| parent | d094cbe998eb566d47552aa9d3c26c9123a7b858 (diff) | |
| download | op-kernel-dev-1af3557abdef34ee036a6de4cb79e24468544b8d.zip op-kernel-dev-1af3557abdef34ee036a6de4cb79e24468544b8d.tar.gz | |
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>
| -rw-r--r-- | fs/sysfs/file.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c index 979e937..b1606e0 100644 --- a/fs/sysfs/file.c +++ b/fs/sysfs/file.c @@ -446,11 +446,11 @@ static unsigned int sysfs_poll(struct file *filp, poll_table *wait) if (buffer->event != atomic_read(&od->event)) goto trigger; - return 0; + return DEFAULT_POLLMASK; trigger: buffer->needs_read_fill = 1; - return POLLERR|POLLPRI; + return DEFAULT_POLLMASK|POLLERR|POLLPRI; } void sysfs_notify_dirent(struct sysfs_dirent *sd) |
