linux-ext4 - Re: [PATCH 2/4 v3] fiemap: add EXTENT_DATA

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20131213110608.GC14884@infradead.org>
Date:	Fri, 13 Dec 2013 03:06:08 -0800
From:	Christoph Hellwig <hch@...radead.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	David Sterba <dsterba@...e.cz>, linux-fsdevel@...r.kernel.org,
	adilger@...ger.ca, linux-nilfs@...r.kernel.org, mfasheh@...e.com,
	xfs@....sgi.com, hch@...radead.org, linux-btrfs@...r.kernel.org,
	viro@...iv.linux.org.uk, linux-ext4@...r.kernel.org,
	ocfs2-devel@....oracle.com
Subject: Re: [PATCH 2/4 v3] fiemap: add EXTENT_DATA_COMPRESSED flag

On Fri, Dec 13, 2013 at 10:24:43AM +1100, Dave Chinner wrote:
> I'd prefer to just see the new physical length field always filled
> out, regardless of whether it is a compressed extent or not. In
> terms of backwards compatibility to userspace, it makes no
> difference because the value of reserved/unused fields is undefined
> by the API. Yes, the implementation zeros them, but there's nothing
> in the documentation that says "reserved fields must be zero".
> Hence I think we should just set it for every extent.
> 
> >From the point of view of the kernel API (fiemap_fill_next_extent),
> passing the physical extent size in the "len" parameter for normal
> extents, then passing 0 for the "physical length" makes absolutely
> no sense.

I tend to agree, but the additional complication here is that this is
a change to an existing API.  We'd need another HAVE_PHYS_LEN flag for
non-compressed extents so that userspace can rely on it.  Given that
it's only useful for that case I think the userspace API introduced
is the best we can get.

I think however that we should always pass the phys_len argument in the
kernel API just to make it less confusing.

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html