Re: [PATCH] Expose SHM_HUGETLB in shmctl(id, IPC_STAT, ...)

[Andrew Morton <akpm@osdl.org>]

Arun Sharma <arun.sharma@google.com> wrote:
>
> Allow shmctl to find out if a shmid corresponds to a HUGETLB segment
> 
>  Signed-off-by: Arun Sharma <arun.sharma@google.com>
>  Acked-by: Rohit Seth <rohit.seth@intel.com>
> 
>  --- a/ipc/shm.c	Tue Nov  8 20:58:38 2005
>  +++ b/ipc/shm.c	Wed Nov  9 10:26:37 2005
>  @@ -197,7 +197,7 @@
>   		return -ENOMEM;
>   
>   	shp->shm_perm.key = key;
>  -	shp->shm_flags = (shmflg & S_IRWXUGO);
>  +	shp->shm_flags = (shmflg & (S_IRWXUGO | SHM_HUGETLB));
>   	shp->mlock_user = NULL;
>   
>   	shp->shm_perm.security = NULL;

I dunno.  The manpage says:

       The highlighted fields in the member shm_perm can be set:

           struct ipc_perm {
       ...
               ushort mode;  /* lower 9 bits of access modes */
       ...
           };

So if an application used to do:

	if (perm.mode == 0666)

it will now break, because we've gone and set bit 9 on hugetlb segments.