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Re: [PATCH 4/6] Ext4: fail if we try to use hole punch

To: Avi Kivity <avi@xxxxxxxxxx>
Subject: Re: [PATCH 4/6] Ext4: fail if we try to use hole punch
From: Josef Bacik <josef@xxxxxxxxxx>
Date: Tue, 16 Nov 2010 11:05:46 -0500
Cc: Josef Bacik <josef@xxxxxxxxxx>, david@xxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-btrfs@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, cmm@xxxxxxxxxx, cluster-devel@xxxxxxxxxx, ocfs2-devel@xxxxxxxxxxxxxx
In-reply-to: <4CE28211.6060204@xxxxxxxxxx>
References: <1289840723-3056-1-git-send-email-josef@xxxxxxxxxx> <1289840723-3056-5-git-send-email-josef@xxxxxxxxxx> <4CE2783F.1020004@xxxxxxxxxx> <20101116125016.GA31957@xxxxxxxxxxxxxxxxxxxxxxxxxx> <4CE28211.6060204@xxxxxxxxxx>
User-agent: Mutt/1.5.19 (2009-01-05)
On Tue, Nov 16, 2010 at 03:07:29PM +0200, Avi Kivity wrote:
> On 11/16/2010 02:50 PM, Josef Bacik wrote:
>> On Tue, Nov 16, 2010 at 02:25:35PM +0200, Avi Kivity wrote:
>> >  On 11/15/2010 07:05 PM, Josef Bacik wrote:
>> >>  Ext4 doesn't have the ability to punch holes yet, so make sure we return
>> >>  EOPNOTSUPP if we try to use hole punching through fallocate.  This 
>> >> support can
>> >>  be added later.  Thanks,
>> >>
>> >
>> >  Instead of teaching filesystems to fail if they don't support the
>> >  capability, why don't supporting filesystems say so, allowing the fail
>> >  code to be in common code?
>> >
>>
>> There is no simple way to test if a filesystem supports hole punching or not 
>> so
>> the check has to be done per fs.  Thanks,
>
> Could put a flag word in superblock_operations.  Filesystems which  
> support punching (or other features) can enable it there.
>
> Or even have its own callback.
>

Sure but then you have to do the same thing for every other flag you add to
fallocate and then you have this huge mess of random flags just so you don't
call into the filesystem.  This way is a lesser of two evils I think.  Thanks,

Josef

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