linux-ext4 - Re: [PATCH 15/34] libext2fs: support BLKZEROOUT/FALLOC_FL_ZERO_RANGE in ext2fs_zero

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Date:	Sun, 21 Sep 2014 22:51:09 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 15/34] libext2fs: support BLKZEROOUT/FALLOC_FL_ZERO_RANGE
 in ext2fs_zero_blocks

On Sat, Sep 13, 2014 at 03:12:53PM -0700, Darrick J. Wong wrote:
> +#if defined(HAVE_FALLOCATE) && defined(FALLOC_FL_ZERO_RANGE)
> +		int flag = FALLOC_FL_ZERO_RANGE;
> +		struct stat statbuf;
> +
> +		/*
> +		 * If we're trying to zero a range past the end of the file,
> +		 * just use regular fallocate to get there, because zeroing
> +		 * a range past EOF does not extend the file.
> +		 */

If we are operating on a regular file (for example, "mkfs.ext4
/tmp/foo.img 64M") we want to keep the file a sparse one; so if we are
trying to zero a range past the end of the file, it should be
sufficient simply use trucate to set i_size.  In fact, if we can use
FALLOC_FL_PUNCH on the regular file, we should try to use that
instead, I would think.

					- Ted
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