ipc: add sysctl to specify desired next object id
Add 3 new variables and sysctls to tune them (by one "next_id" variable
for messages, semaphores and shared memory respectively). This variable
can be used to set desired id for next allocated IPC object. By default
it's equal to -1 and old behaviour is preserved. If this variable is
non-negative, then desired idr will be extracted from it and used as a
start value to search for free IDR slot.
Notes:
1) this patch doesn't guarantee that the new object will have desired
id. So it's up to user space how to handle new object with wrong id.
2) After a sucessful id allocation attempt, "next_id" will be set back
to -1 (if it was non-negative).
[akpm@linux-foundation.org: checkpatch fixes]
Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/ipc/util.h b/ipc/util.h
index c8fe2f7..a61e0ca 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -92,6 +92,7 @@
#define IPC_SHM_IDS 2
#define ipcid_to_idx(id) ((id) % SEQ_MULTIPLIER)
+#define ipcid_to_seqx(id) ((id) / SEQ_MULTIPLIER)
/* must be called with ids->rw_mutex acquired for writing */
int ipc_addid(struct ipc_ids *, struct kern_ipc_perm *, int);