linux-kernel - Re: [dm-devel] [PATCH][RFC] dm: Do not open log and cow device read-write for read-only mappings

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Date:	Tue, 15 Feb 2011 15:46:25 +0000
From:	Alasdair G Kergon <agk@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	device-mapper development <dm-devel@...hat.com>,
	Milan Broz <mbroz@...hat.com>, Jens Axboe <axboe@...nel.dk>,
	Tao Ma <tm@....ma>, linux-kernel@...r.kernel.org
Subject: Re: [dm-devel] [PATCH][RFC] dm: Do not open log and cow device
	read-write for read-only mappings

On Tue, Feb 15, 2011 at 04:20:33PM +0100, Tejun Heo wrote:
> Hmmm... but -EACCES is the correct one here.  The device node itself
> is rejecting RW access.  There's no FS which is enforcing RO.

Exactly:)  If the filesystem permissions were what was blocking this
(say r--) then I'd agree with EACCES.  Interpret those man pages in the
context of 'pathname refers to a block device not a file'.

If it's EACCES, I just need to gain more privilege/capabilities and then
repeat the system call and it could succeed.

But EROFS tells me however much extra privilege I get it's going to make
no difference.

That's why I'm arguing EACCES is not a good error to return and EROFS is
more appropriate.

Alasdair

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