xfs
[Top] [All Lists]

Re: [dm-devel] Re: [PATCH 3/3] Add timeout feature

To: Takashi Sato <t-sato@xxxxxxxxxxxxx>
Subject: Re: [dm-devel] Re: [PATCH 3/3] Add timeout feature
From: Alasdair G Kergon <agk@xxxxxxxxxx>
Date: Tue, 1 Jul 2008 11:52:51 +0100
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, axboe@xxxxxxxxx, mtk.manpages@xxxxxxxxxxxxxx, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>, "dm-devel@xxxxxxxxxx" <dm-devel@xxxxxxxxxx>, viro@xxxxxxxxxxxxxxxxxx, "linux-fsdevel@xxxxxxxxxxxxxxx" <linux-fsdevel@xxxxxxxxxxxxxxx>, akpm@xxxxxxxxxxxxxxxxxxxx, "linux-ext4@xxxxxxxxxxxxxxx" <linux-ext4@xxxxxxxxxxxxxxx>
In-reply-to: <20080701081026.GB16691@xxxxxxxxxxxxx>
Mail-followup-to: Takashi Sato <t-sato@xxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, axboe@xxxxxxxxx, mtk.manpages@xxxxxxxxxxxxxx, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>, "dm-devel@xxxxxxxxxx" <dm-devel@xxxxxxxxxx>, viro@xxxxxxxxxxxxxxxxxx, "linux-fsdevel@xxxxxxxxxxxxxxx" <linux-fsdevel@xxxxxxxxxxxxxxx>, akpm@xxxxxxxxxxxxxxxxxxxx, "linux-ext4@xxxxxxxxxxxxxxx" <linux-ext4@xxxxxxxxxxxxxxx>
Organization: Red Hat UK Ltd. Registered in England and Wales, number 03798903. Registered Office: Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SL4 1TE.
References: <20080630212450t-sato@xxxxxxxxxxxxxxx> <20080701081026.GB16691@xxxxxxxxxxxxx>
Sender: xfs-bounce@xxxxxxxxxxx
User-agent: Mutt/1.4.1i
On Tue, Jul 01, 2008 at 04:10:26AM -0400, Christoph Hellwig wrote:
> I still disagree with this whole patch.  

Same here - if you want a timeout, what stops you from implementing it in a
userspace process?  If your concern is that the process might die without
thawing the filesystem, take a look at the userspace LVM/multipath code for
ideas - lock into memory, disable OOM killer, run from ramdisk etc.
In practice, those techniques seem to be good enough.

> call can hang and this would be theoretically useful is when the
> filesystem is already frozen by someone else, but this should be fixed
> by refusing to do the second freeze, as suggested in my comment to patch
> 1.

Similarly if a device-mapper device is involved, how should the following
sequence behave - A, B or C?

1. dmsetup suspend (freezes)
2. FIFREEZE
3. FITHAW
4. dmsetup resume (thaws)

A:
  1 succeeds, freezes
  2 succeeds, remains frozen
  3 succeeds, remains frozen
  4 succeeds, thaws

B:
  1 succeeds, freezes
  2 fails, remains frozen
  3 shouldn't be called because 2 failed but if it is: succeeds, thaws
  4 succeeds (already thawed, but still does the device-mapper parts)

C:
  1 succeeds, freezes
  2 fails, remains frozen
  3 fails (because device-mapper owns the freeze/thaw), remains frozen 
  4 succeeds, thaws

Alasdair
-- 
agk@xxxxxxxxxx


<Prev in Thread] Current Thread [Next in Thread>