linux-kernel - Re: [RFC 1/9] block: add llseek(SEEK_HOLE/SEEK

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Date: Thu, 28 Mar 2024 18:50:21 -0500
From: Eric Blake <eblake@...hat.com>
To: Stefan Hajnoczi <stefanha@...hat.com>
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Alasdair Kergon <agk@...hat.com>, Mikulas Patocka <mpatocka@...hat.com>, dm-devel@...ts.linux.dev, 
	David Teigland <teigland@...hat.com>, Mike Snitzer <snitzer@...nel.org>, Jens Axboe <axboe@...nel.dk>, 
	Christoph Hellwig <hch@....de>, Joe Thornber <ejt@...hat.com>
Subject: Re: [RFC 1/9] block: add llseek(SEEK_HOLE/SEEK_DATA) support

On Thu, Mar 28, 2024 at 04:39:02PM -0400, Stefan Hajnoczi wrote:
> The SEEK_HOLE/SEEK_DATA interface is used by userspace applications to
> detect sparseness. This makes copying and backup applications faster and
> reduces space consumption because only ranges that do not contain data
> can be skipped.

s/only //

> 
> Handle SEEK_HOLE/SEEK_DATA for block devices. No block drivers implement
> the new callback yet so the entire block device will appear to contain
> data. Later patches will add support to drivers so this actually becomes
> useful.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@...hat.com>
> ---
>  include/linux/blkdev.h |  7 +++++++
>  block/fops.c           | 43 +++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 49 insertions(+), 1 deletion(-)
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org