Re: [PATCH v2] ipc,shm: document new limits in the uapi header

[Michael Kerrisk (man-pages)]

On Tue, May 13, 2014 at 3:35 AM, Davidlohr Bueso <davidlohr@xxxxxx> wrote:
> On Mon, 2014-05-12 at 09:44 +0200, Michael Kerrisk (man-pages) wrote:
[...]
>> The problem is that part of your text is still broken grammatically In
>> particular, the piece "Both SHMMAX and SHMALL have their default
>> values to the maximum limit" at the very least lacks a word. That's
>> what prompted me to propose the alternative, rather than just say
>> "this is wrong"--and I thought that I might as well make a more
>> thoroughgoing attempt at helping improve the text.
>>
>> I agree that text something like this should land in the man page at
>> some point, but as long as we're going to the trouble to improve the
>> comments in the code, let's make them as good and helpful as we can.
>
> Fair enough, and I trust your grammar corrections over mine ;) Thanks
> for taking a closer look. I've added your text below.

Thanks.

Acked-by: Michael Kerrisk <mtk.manpages@xxxxxxxxx>

Cheers,'

Michael

> 8<------------------------------------------
> From: Davidlohr Bueso <davidlohr@xxxxxx>
> Subject: [PATCH v3] ipc,shm: document new limits in the uapi header
>
> This is useful in the future and allows users to
> better understand the reasoning behind the changes.
>
> Signed-off-by: Davidlohr Bueso <davidlohr@xxxxxx>
> ---
>  include/uapi/linux/shm.h | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/include/uapi/linux/shm.h b/include/uapi/linux/shm.h
> index 74e786d..1fbf24e 100644
> --- a/include/uapi/linux/shm.h
> +++ b/include/uapi/linux/shm.h
> @@ -8,17 +8,20 @@
>  #endif
>
>  /*
> - * SHMMAX, SHMMNI and SHMALL are upper limits are defaults which can
> - * be modified by sysctl.
> + * SHMMNI, SHMMAX and SHMALL are default upper limits which can be
> + * modified by sysctl. The SHMMAX and SHMALL values have been chosen to
> + * be as large possible without facilitating scenarios where userspace
> + * causes overflows when adjusting the limits via operations of the form
> + * "retrieve current limit; add X; update limit". It is therefore not
> + * advised to make SHMMAX and SHMALL any larger. These limits are
> + * suitable for both 32 and 64-bit systems.
>   */
> -
>  #define SHMMIN 1                        /* min shared seg size (bytes) */
>  #define SHMMNI 4096                     /* max num of segs system wide */
> -#define SHMMAX (ULONG_MAX - (1L<<24))   /* max shared seg size (bytes) */
> -#define SHMALL (ULONG_MAX - (1L<<24))   /* max shm system wide (pages) */
> +#define SHMMAX (ULONG_MAX - (1UL << 24)) /* max shared seg size (bytes) */
> +#define SHMALL (ULONG_MAX - (1UL << 24)) /* max shm system wide (pages) */
>  #define SHMSEG SHMMNI                   /* max shared segs per process */
>
> -
>  /* Obsolete, used only for backwards compatibility and libc5 compiles */
>  struct shmid_ds {
>         struct ipc_perm         shm_perm;       /* operation perms */
> --
> 1.8.1.4
>
>
>
>



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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