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

Signed-off-by: Kirill A. Shutemov <redacted>
Cc: Andi Kleen <andi-Vw/NltI1exuRpAAqCnN02g@public.gmane.org>
Cc: Ingo Molnar <redacted>
Cc: Arjan van de Ven <redacted>
Cc: Hugh Dickins <redacted>
Cc: KOSAKI Motohiro <redacted>
Cc: Alan Cox <alan-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org>
Cc: Ulrich Drepper <redacted>
Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.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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