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Subject[PATCH, RFC] shmat: introduce flag SHM_MAP_HINT
Date
It allows interpret attach address as a hint, not as exact address.

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: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/shm.h | 1 +
ipc/shm.c | 4 ++--
2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/shm.h b/include/linux/shm.h
index eca6235..2a637b8 100644
--- a/include/linux/shm.h
+++ b/include/linux/shm.h
@@ -55,6 +55,7 @@ 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_HINT 0200000 /* interpret attach address as a hint */

/* super user shmctl commands */
#define SHM_LOCK 11
diff --git a/ipc/shm.c b/ipc/shm.c
index e77ec69..19462bb 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_HINT) && (addr & (SHMLBA-1))) {
if (shmflg & SHM_RND)
addr &= ~(SHMLBA-1); /* round down */
else
@@ -828,7 +828,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
#endif
goto out;
}
- flags = MAP_SHARED | MAP_FIXED;
+ flags = (shmflg & SHM_MAP_HINT ? 0 : MAP_FIXED) | MAP_SHARED;
} else {
if ((shmflg & SHM_REMAP))
goto out;
--
1.5.6.5.GIT


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