linux-kernel - Re: writing file to disk: not as easy as it looks

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Message-ID: <20081203175223.5694ca76@lxorguk.ukuu.org.uk>
Date:	Wed, 3 Dec 2008 17:52:23 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
Cc:	Pavel Machek <pavel@...e.cz>, Theodore Tso <tytso@....edu>,
	Chris Friesen <cfriesen@...tel.com>,
	kernel list <linux-kernel@...r.kernel.org>, aviro@...hat.com
Subject: Re: writing file to disk: not as easy as it looks

> error reported for one filesystem may belong to the data written by other 
> filesystem. So should some flag "there was an error" be set for all 
> partitions and report it to every filesystem when it does cache flush? Or 
> record the time of the last error in the driver and let the filesystem 
> query it (so that the filesystem can tell if the error happened before or 
> after it was mounted).

Good question - not working that high up the stack I don't know the right
answer there.
> 
> BTW. how does SCSI report cache flush errors? Does it report them on 
> SYNCHRONIZE CACHE command or does it report them on defered senses?

Not sure. I thought the same way.

> Another point is that unless the sector remap table is full, there should 
> be no cache flush errors.

You can get them on partial writes to large sector devices, assorted
errors on SSD devices and various 'catastrophic' errors.

> I meant for example loose cable or so --- does it make sense to retry 
> indefinitely (until the admin plugs the cable or unmounts the filesystem) 
> or return error to the filesystem after few retries?

At the low level we have to return an error so that RAID and the like can
work.

Alan
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