linux-kernel - Re: [PATCH 3/3] block: implement (some of) fallocate for block devices

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Date:	Sat, 5 Mar 2016 12:58:34 -0800
From:	Christoph Hellwig <hch@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Darrick J. Wong" <darrick.wong@...cle.com>,
	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@...radead.org>,
	Theodore Ts'o <tytso@....edu>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Linux API <linux-api@...r.kernel.org>,
	Dave Chinner <david@...morbit.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	shane.seymour@....com, Bruce Fields <bfields@...ldses.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Jeff Layton <jlayton@...chiereds.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/3] block: implement (some of) fallocate for block
 devices

On Fri, Mar 04, 2016 at 07:13:25PM -0800, Linus Torvalds wrote:
> > +       /* We can't change the bdev size from here */
> > +       if (!(mode & FALLOC_FL_KEEP_SIZE))
> > +               return -EOPNOTSUPP;
> 
> Oh, and this I think is wrong.
> 
> The thing is, FALLOC_FL_KEEP_SIZE is only supposed to matter if the
> region is outside the existing length.

For allocations...

> So if y ou punch a hole in the middle of a file, you don't need
> FALLOC_FL_KEEP_SIZE.

For FALLOC_FL_PUNCH_HOLE we always require FALLOC_FL_KEEP_SIZE so far,
and I'd rather not change things for block devices just because we can.