linux-ext4 - Re: ext4 filesystem bad extent error review

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Date:	Fri, 03 Jan 2014 11:54:12 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
CC:	"Huang Weller (CM/ESW12-CN)" <Weller.Huang@...bosch.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"Juergens Dirk (CM-AI/ECO2)" <Dirk.Juergens@...bosch.com>
Subject: Re: ext4 filesystem bad extent error review

On 1/3/14, 11:51 AM, Theodore Ts'o wrote:
> On Fri, Jan 03, 2014 at 11:23:54AM -0600, Eric Sandeen wrote:
>>> The BLKFLSBUF ioctl does __not__ send a CACHE FLUSH command to the
>>> hardware device.  It forces all of the dirty buffers in memory to the
>>> storage device, and then it invalidates all the buffer cache, but it
>>> does not send a CACHE FLUSH command to the hardware.  Hence, the
>>> hardware is free to write it to its on-disk cache, and not necessarily
>>> guarantee that the data is written to stable store.  (For an example
>>> use case of BLKFLSBUF, we use it in e2fsck to drop the buffer cache
>>> for benchmarking purposes.)
>>
>> Are you sure?  for a bdev w/ ext4 on it:
>>
>> BLKFLSBUF
>> 	fsync_bdev
>> 		sync_filesystem
>> 			sync_fs
>> 				ext4_sync_fs
>> 					blkdev_issue_flush
> 
> This call chain only happens if the block device is mounted.

Sure, but I thought that's what they were doing.  Maybe I misread.

-Eric


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