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

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Message-ID: <20101116163320.GB2524@localhost.localdomain>
Date:	Tue, 16 Nov 2010 11:33:21 -0500
From:	Josef Bacik <josef@...hat.com>
To:	Pádraig Brady <P@...igBrady.com>
Cc:	Josef Bacik <josef@...hat.com>, david@...morbit.com,
	linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	xfs@....sgi.com, cmm@...ibm.com, cluster-devel@...hat.com,
	ocfs2-devel@....oracle.com
Subject: Re: [PATCH 4/6] Ext4: fail if we try to use hole punch

On Tue, Nov 16, 2010 at 04:20:43PM +0000, Pádraig Brady wrote:
> On 15/11/10 17:05, 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,
> > 
> > Signed-off-by: Josef Bacik <josef@...hat.com>
> > ---
> >  fs/ext4/extents.c |    4 ++++
> >  1 files changed, 4 insertions(+), 0 deletions(-)
> > 
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index 0554c48..35bca73 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -3622,6 +3622,10 @@ long ext4_fallocate(struct inode *inode, int mode, loff_t offset, loff_t len)
> >  	struct ext4_map_blocks map;
> >  	unsigned int credits, blkbits = inode->i_blkbits;
> >  
> > +	/* We only support the FALLOC_FL_KEEP_SIZE mode */
> > +	if (mode && (mode != FALLOC_FL_KEEP_SIZE))
> > +		return -EOPNOTSUPP;
> > +
> >  	/*
> >  	 * currently supporting (pre)allocate mode for extent-based
> >  	 * files _only_
> 
> So for older versions of ext4 or other filesystems, how do we know
> that fallocate(...,FALLOC_FL_PUNCH_HOLE) is not supported.
> I.E. how do we detect at runtime that the call succeeded
> and didn't just do a normal fallocate()?
>

Older kernels won't accept FALLOC_FL_PUNCH_HOLE, so you'll get an error.
Thanks,

Josef 
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