From: Eric Sandeen <sandeen@redhat.com>
To: "Theodore Ts'o" <tytso@mit.edu>
Cc: Gordan Bobic <gordan@bobich.net>, linux-ext4@vger.kernel.org
Subject: Re: e2fsprogs alignment issues
Date: Wed, 11 Jul 2012 16:26:08 -0500 [thread overview]
Message-ID: <4FFDEF70.3090202@redhat.com> (raw)
In-Reply-To: <20120711200557.GB5838@thunk.org>
On 7/11/12 3:05 PM, Theodore Ts'o wrote:
> On Wed, Jul 11, 2012 at 10:04:51AM -0500, Eric Sandeen wrote:
...
>> I think Gordan suggested (if I understand it
>> right) that doing an array of ints might also solve the problem, since
>> ints should be on natural alignment. Or maybe in some cases malloc/free
>> would be more obvious, if handling errors isn't too tricky.
>
> In the specific case which Gordon has pointed out, the obvious thing
> to do is to just to set errno to ENOMEM, and return -1. since we
> already reflect an error code up to the caller if the FIEMAP ioctl()
> fails.
>
> If someone sends me the patch, I will happily apply it.
Sure, I was planning on it :)
>> (IIRC "make gcc-wall" will also emit warnings for casts which change
>> natural alignment, among other things)
>
> I'd have to check to be sure, but I don't think so, since it would
> have way too many false positives. We *do* have code where we take
> char *'s and and then cast them to some other pointer type, and then
> dereference them. And we do currently assume that it is safe to do
> this for on-disk data structures which are 4 byte aligned, in the
> directory entry code, for example.
>
> I will *not* accept a patch which uses memcpy to copy each field in
> the on-disk superblock, or directory entry, into an int, just in case
> there is some insane architecture which requires that 4 byte integers
> be 32-byte aligned, or something else insane like that.
Well, let's just see where we're at, first, and see what it'll take,
case by case.
-Eric
next prev parent reply other threads:[~2012-07-11 21:26 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-11 13:20 e2fsprogs alignment issues Gordan Bobic
2012-07-11 15:04 ` Eric Sandeen
2012-07-11 20:05 ` Theodore Ts'o
2012-07-11 21:22 ` Gordan Bobic
2012-07-12 0:05 ` Theodore Ts'o
2012-07-11 21:26 ` Eric Sandeen [this message]
2012-07-13 22:25 ` Dave Chinner
2012-07-11 21:24 ` Gordan Bobic
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