Re: [PATCH, v3] shmat: introduce flag SHM_MAP_NOT_FIXED

[Michael Kerrisk]

Kirill,

On Tue, Oct 7, 2008 at 6:15 PM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote:
> If SHM_MAP_NOT_FIXED specified and shmaddr is not NULL, then the kernel takes
> shmaddr as a hint about where to place the mapping. The address of the mapping
> is returned as the result of the call.
>
> It's similar to mmap() without MAP_FIXED.

Please CC linux-api@xxxxxxxxxxxxxxx on patches that change the
kernel-userspace interface.

Cheers,

Michael

> Signed-off-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
> Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxx>
> Cc: Hugh Dickins <hugh@xxxxxxxxxxx>
> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Cc: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
> Cc: Ulrich Drepper <drepper@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>  include/linux/shm.h |    2 ++
>  ipc/shm.c           |    7 ++++---
>  2 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/shm.h b/include/linux/shm.h
> index eca6235..fd288eb 100644
> --- a/include/linux/shm.h
> +++ b/include/linux/shm.h
> @@ -55,6 +55,8 @@ struct shmid_ds {
>  #define        SHM_RND         020000  /* round attach address to SHMLBA boundary */
>  #define        SHM_REMAP       040000  /* take-over region on attach */
>  #define        SHM_EXEC        0100000 /* execution access */
> +#define        SHM_MAP_NOT_FIXED 0200000 /* interpret attach address as a search
> +                                  * hint */
>
>  /* super user shmctl commands */
>  #define SHM_LOCK       11
> diff --git a/ipc/shm.c b/ipc/shm.c
> index e77ec69..54f3c61 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -819,7 +819,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
>        if (shmid < 0)
>                goto out;
>        else if ((addr = (ulong)shmaddr)) {
> -               if (addr & (SHMLBA-1)) {
> +               if (!(shmflg & SHM_MAP_NOT_FIXED) && (addr & (SHMLBA-1))) {
>                        if (shmflg & SHM_RND)
>                                addr &= ~(SHMLBA-1);       /* round down */
>                        else
> @@ -828,7 +828,8 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
>  #endif
>                                        goto out;
>                }
> -               flags = MAP_SHARED | MAP_FIXED;
> +               flags = MAP_SHARED |
> +                               (shmflg & SHM_MAP_NOT_FIXED ? 0 : MAP_FIXED);
>        } else {
>                if ((shmflg & SHM_REMAP))
>                        goto out;
> @@ -892,7 +893,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
>        sfd->vm_ops = NULL;
>
>        down_write(&current->mm->mmap_sem);
> -       if (addr && !(shmflg & SHM_REMAP)) {
> +       if (addr && !(shmflg & (SHM_REMAP|SHM_MAP_NOT_FIXED))) {
>                err = -EINVAL;
>                if (find_vma_intersection(current->mm, addr, addr + size))
>                        goto invalid;
> --
> 1.5.6.5.GIT
>
> --
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-- 
Michael Kerrisk Linux man-pages maintainer;
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