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

To: Josef Bacik <josef@xxxxxxxxxx>
Subject: Re: [PATCH 4/6] Ext4: fail if we try to use hole punch
From: Pádraig Brady <P@xxxxxxxxxxxxxx>
Date: Tue, 16 Nov 2010 16:20:43 +0000
Cc: 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: <1289840723-3056-5-git-send-email-josef@xxxxxxxxxx>
References: <1289840723-3056-1-git-send-email-josef@xxxxxxxxxx> <1289840723-3056-5-git-send-email-josef@xxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3
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@xxxxxxxxxx>
> ---
>  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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