On Thu, Aug 18, 2005 at 02:24:25PM +0200, Bartlomiej Zolnierkiewicz wrote:
> Hi,
>
> On 8/18/05, Tejun Heo <[EMAIL PROTECTED]> wrote:
> > Steven Scholz wrote:
> > > Tejun Heo wrote:
> > >
> > >> Steven Scholz wrote:
> > >>
> > >>> Hi there,
> > >>>
> > >>> According to an (old) man page of sync(2)
> > >>>
> > >>> According to the standard specification (e.g., SVID),
> > >>> sync() schedules the writes, but may return before the
> > >>> actual writing is done. However, since version 1.3.20
> > >>> Linux does actually wait. (This still does not guarantee
> > >>> data integrity: modern disks have large caches.)
> > >>>
> > >>> How about recent kernels? Does sync() block until buffers are flushed?
> > >>> How can I find out if the disk caches are actually flushed?
> > >>>
> > >>> I want to make sure that all data is flushed to my disk drive before
> > >>> powering down the system.
> > >>>
> > >>> Thanks.
> > >>>
> > >>
> > >> All disk caches are flushed before shutdown via the following path.
> > >>
> > >> kernel/sys.c::sys_reboot()
> > >> kernel/drivers/base/power/shutdown.c::device_shutdown()
> > >> driver specific ->shutdown callback, for ide disks, the path is
> > >> drivers/ide/ide-disk.c::ide_device_shutdown()
> > >> drivers/ide/ide-disk.c::ide_cacheflush_p()
> > >> drivers/ide/ide-disk.c::do_idedisk_flushcache()
> > >>
> > >> And, AFAIK, sync() doesn't flush disk caches.
> > >
> > >
> > > How about umount?
> > >
> >
> > [CC'ing Bartlomiej (Hi!)]
> >
> > Hmmm, umount doesn't. I think maybe adding cache flushing to sync and
> > umount can be helpful.
>
> I think that cache is flushed on umount through idedisk_release().
>
Ah... right. I was testing while another partition is still mounted.
> > And one more thing, ide-disk doesn't flush cache when shutting down.
> > It flushes only when rebooting.
>
> Please see ide_disk_remove().
>
Hmmm, disks are not removed on shutdown, so it's not called on
shutdown.
> > from ide_device_shutdown()...
> >
> > #ifdef CONFIG_ALPHA
> > /* On Alpha, halt(8) doesn't actually turn the machine off,
> > it puts you into the sort of firmware monitor. Typically,
> > it's used to boot another kernel image, so it's not much
> > different from reboot(8). Therefore, we don't need to
> > spin down the disk in this case, especially since Alpha
> > firmware doesn't handle disks in standby mode properly.
> > On the other hand, it's reasonably safe to turn the power
> > off when the shutdown process reaches the firmware prompt,
> > as the firmware initialization takes rather long time -
> > at least 10 seconds, which should be sufficient for
> > the disk to expire its write cache. */
> > if (system_state != SYSTEM_POWER_OFF) {
> > #else
> > if (system_state == SYSTEM_RESTART) {
> > #endif
> > ide_cacheflush_p(drive);
> > return;
> > }
> >
> > It seems that the if clause are there due to some historic thing. The
> > comment suggests that the body in the if clause spun down the drive
> > previously, and we needed the if to avoid spinning down unnecessarily,
> > and the if is left there after we changed the body to flush cache.
>
> It is a correct workaround for Alpha firmware, please see the original patch:
> http://linux.bkbits.net:8080/linux-2.6/[EMAIL
> PROTECTED]|src/|src/drivers|src/drivers/ide|related/drivers/ide/ide-disk.c
>
> The thing is that we want to avoid calling dev->bus->suspend() on
> system_state == SYSTEM_HALT.
Oh.. right. We're calling either cacheflush_p or suspend and as
suspending implies flushing, we should be okay. Sorry about
unnecessary noise.
Steven, ide-disk's are correctly flushed on shutdown and umount.
Again, sorry about the confusion.
Thanks.
--
tejun
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