linux-ext4 - Re: [PATCH 4/6] Ext4: fail if we try to use hole punch

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Date:	Tue, 16 Nov 2010 16:20:43 +0000
From:	Pádraig Brady <P@...igBrady.com>
To:	Josef Bacik <josef@...hat.com>
CC:	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 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()?

cheers,
Pádraig.
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