lkml.org 
[lkml]   [2000]   [Dec]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [Patch] shmmin behaviour back to 2.2 behaviour
From
Date
Andries Brouwer <aeb@veritas.com> writes:

> On Wed, Dec 27, 2000 at 01:16:44PM -0200, Marcelo Tosatti wrote:
> I happen to see this post, but have not followed earlier discussion.
> See a patch fragment

(The patch does not show a lot of context. You should look at the
whole files)

>
> -#define SHMMIN 0 /* min shared seg size (bytes) */
> +#define SHMMIN 1 /* min shared seg size (bytes) */
>
> + if (size < SHMMIN || size > shm_ctlmax)
> + return -EINVAL;
>
> My first reaction is that this patch is broken, since
> one usually specifies size 0 in shmget to get an existing
> bit of shared memory (with known key but unknown size).

That's still covert: The check is moved out of shmget into the create
function. So you cannot create segments of size 0 but you can get
existing segments by giving a size 0.

> [Was this rehashed in earlier discussion? I wonder whether there
> are any reasons to forbid size 0. Forbidding size 0 is
> allowed by SUSv2 as I read it - it says
>
> The shmget() function will fail if:
>
> [EINVAL]
> The value of size is less than the system-imposed minimum
> or greater than the system-imposed maximum,

We match this with a system-imposed minimum of 1 now.

> or a shared memory identifier exists for the argument key
> but the size of the segment associated with it is less
> than size and size is not 0.

We don't match this exactly since we allow arbitrary sizes smaller
than segment size for existing segments (0 included).

> but is contrary to AIX, which says
>
> EINVAL
> A shared memory identifier does not exist and the Size
> parameter is less than the system-imposed minimum or greater
> than the system-imposed maximum.
> EINVAL
> A shared memory identifier exists for the Key parameter,
> but the size of the segment associated with it is less than
> the Size parameter, and the Size parameter is not equal to 0.

That's what we do and always did.

So should we go for SUSv2? I do not think that we should restrict the
shmget so late in the release cycle. We could enhance this check
further in 2.5 perhaps.

Greetings
Christoph

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 12:52    [W:0.069 / U:8.548 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site