Re: when are buffers/caches flushed?

[Steven Scholz <steven.scholz@imc-berlin.de>]

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?

--
Steven




-- 
Steven Scholz

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