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SubjectRe: [PATCH, v3] shmat: introduce flag SHM_MAP_NOT_FIXED
Kirill,

On Tue, Oct 7, 2008 at 6:15 PM, Kirill A. Shutemov <kirill@shutemov.name> 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@vger.kernel.org on patches that change the
kernel-userspace interface.

Cheers,

Michael

> Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
> Cc: Andi Kleen <andi@firstfloor.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Arjan van de Ven <arjan@infradead.org>
> Cc: Hugh Dickins <hugh@veritas.com>
> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
> Cc: Ulrich Drepper <drepper@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
> 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;
http://www.kernel.org/doc/man-pages/ Found a documentation bug?
http://www.kernel.org/doc/man-pages/reporting_bugs.html


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