linux-kernel - Re: [PATCH 2/2] block: create ioctl to discard-or-zeroout a range of blocks

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Date:	Fri, 11 Mar 2016 10:25:30 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Ric Wheeler <rwheeler@...hat.com>,
	"Theodore Ts'o" <tytso@....edu>, Gregory Farnum <greg@...gs42.com>,
	Dave Chinner <david@...morbit.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Christoph Hellwig <hch@...radead.org>,
	"Darrick J. Wong" <darrick.wong@...cle.com>,
	Jens Axboe <axboe@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux API <linux-api@...r.kernel.org>,
	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>,
	Eric Sandeen <esandeen@...hat.com>
Subject: Re: [PATCH 2/2] block: create ioctl to discard-or-zeroout a range of blocks

On Fri, Mar 11, 2016 at 9:30 AM, Andy Lutomirski <luto@...capital.net> wrote:
>
> What if we had an ioctl to do these data-leaking operations that took,
> as an extra parameter, an fd to the block device node.  They allow
> access if the fd points to the right inode and has FMODE_READ (and LSM
> checks say it's okay).  Sure, it's awkward, but it's much safer.

That sounds absolutely horrible.

I'd *much* prefer the suggestion from Alan to simply have a mount-time
option to enable it. That way, you will never get any surprises, and
no "subtle new behavior for somebody who set their system up in a way
that doesn't allow for this".

So you'd have to explicitly say "my setup is ok with hole punching".

                Linus