Re: [PATCH 2/4] ext3: truncate block allocated on a failed ext3_write_begin

[Andrew Morton <akpm@linux-foundation.org>]

On Sat, 13 Sep 2008 11:32:49 -0400
"Theodore Ts'o" <tytso@MIT.EDU> wrote:

> From: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> 
> For blocksize < pagesize we need to remove blocks that got allocated in
> block_write_begin() if we fail with ENOSPC for later blocks.
> block_write_begin() internally does this if it allocated page
> locally. This makes sure we don't have blocks outside inode.i_size
> during ENOSPC.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> Cc: linux-ext4@vger.kernel.org
> ---
>  fs/ext3/inode.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/fs/ext3/inode.c b/fs/ext3/inode.c
> index 507d868..bff22b9 100644
> --- a/fs/ext3/inode.c
> +++ b/fs/ext3/inode.c
> @@ -1178,6 +1178,13 @@ write_begin_failed:
>  		ext3_journal_stop(handle);
>  		unlock_page(page);
>  		page_cache_release(page);
> +		/*
> +		 * block_write_begin may have instantiated a few blocks
> +		 * outside i_size.  Trim these off again. Don't need
> +		 * i_size_read because we hold i_mutex.
> +		 */
> +		if (pos + len > inode->i_size)
> +			vmtruncate(inode, inode->i_size);
>  	}
>  	if (ret == -ENOSPC && ext3_should_retry_alloc(inode->i_sb, &retries))
>  		goto retry;

Well we used to do this trimming in core VFS, but Nick broke it.  We
still do it if the fs doesn't implement ->write_begin().

Should we do this trimming in pagecache_write_begin() in both cases?