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

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Message-ID: <20160305205728.GA4834@infradead.org>
Date:	Sat, 5 Mar 2016 12:57:28 -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 07:06:38PM -0800, Linus Torvalds wrote:
> > +       if ((mode & FALLOC_FL_PUNCH_HOLE) &&
> > +           (!blk_queue_discard(q) || !q->limits.discard_zeroes_data))
> > +               return -EOPNOTSUPP;
> 
> I'm ok with this, but suspect that some users would prefer to just
> turn this into ZERO_RANGE silently.
> 
> Comments from people who would be expected to use this?

A hole punch should be a hole punch, and not silently allocate blocks
isntead of deallocating them.  It's not even a fallback, it's pretty
much the opposite for some workloads.