linux-kernel - Re: Correct parameter size for BLKSSZGET ioctl.

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Date:	Sat, 2 Nov 2013 19:44:51 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Jason Cipriani <jason.cipriani@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	util-linux@...r.kernel.org
Subject: Re: Correct parameter size for BLKSSZGET ioctl.

On Fri, Nov 01, 2013 at 08:29:26PM -0400, Jason Cipriani wrote:
> In blkdiscard in util-linux, at least since version 2.23, the
> following code is used to retrieve a device's physical sector size:
> 
>   uint64_t secsize;
>   ioctl(fd, BLKSSZGET, &secsize);
> 
> On my machine (Ubuntu 12.04 -- 3.2.0-55-generic-pae #85-Ubuntu SMP Wed
> Oct 2 14:03:15 UTC 2013 i686 i686 i386 GNU/Linux) this yields
> incorrect results as it seems a 32-bit int is expected, this causes
> subsequent sector alignment calculations in blkdiscard to be
> incorrect, which in turn causes blkdiscards trim ioctl's to fail in
> certain situations (or even worse, to trim the wrong blocks).

BLKSSZGET returns an int.  If you look at the sources of util-linux
v2.23, you'll see it passes an int to BLKSSZGET in 

	sys-utils/blkdiscard.c
	lib/blkdev.c

E2fsprogs also expects BLKSSZGET to return an int, and if you look at
the kernel sources, it very clearly returns an int.

The one place it doesn't is in sys-utils/blkdiscard.c, where as you
have noted, it is passing in a uint64 to BLKSSZGET.  This looks like
it's a bug in sys-util/blkdiscard.c.

I'll send a proposed patch in the next e-mail message.

     	    	     	      	  - Ted
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