Re: Correct parameter size for BLKSSZGET ioctl.

From: Theodore Ts'o
Date: Sat Nov 02 2013 - 19:45:34 EST

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


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
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at