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>

1 files changed, 32 insertions, 0 deletions

diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
index 00fba2bab87d..130dfece27ac 100644
--- a/ipc/ipc_sysctl.c
+++ b/ipc/ipc_sysctl.c
@@ -158,6 +158,9 @@ static int proc_ipcauto_dointvec_minmax(ctl_table *table, int write,
 
 static int zero;
 static int one = 1;
+#ifdef CONFIG_CHECKPOINT_RESTORE
+static int int_max = INT_MAX;
+#endif
 
 static struct ctl_table ipc_kern_table[] = {
         {
@@ -227,6 +230,35 @@ static struct ctl_table ipc_kern_table[] = {
                 .extra1         = &zero,
                 .extra2         = &one,
         },
+#ifdef CONFIG_CHECKPOINT_RESTORE
+        {
+                .procname       = "sem_next_id",
+                .data           = &init_ipc_ns.ids[IPC_SEM_IDS].next_id,
+                .maxlen         = sizeof(init_ipc_ns.ids[IPC_SEM_IDS].next_id),
+                .mode           = 0644,
+                .proc_handler   = proc_ipc_dointvec_minmax,
+                .extra1         = &zero,
+                .extra2         = &int_max,
+        },
+        {
+                .procname       = "msg_next_id",
+                .data           = &init_ipc_ns.ids[IPC_MSG_IDS].next_id,
+                .maxlen         = sizeof(init_ipc_ns.ids[IPC_MSG_IDS].next_id),
+                .mode           = 0644,
+                .proc_handler   = proc_ipc_dointvec_minmax,
+                .extra1         = &zero,
+                .extra2         = &int_max,
+        },
+        {
+                .procname       = "shm_next_id",
+                .data           = &init_ipc_ns.ids[IPC_SHM_IDS].next_id,
+                .maxlen         = sizeof(init_ipc_ns.ids[IPC_SHM_IDS].next_id),
+                .mode           = 0644,
+                .proc_handler   = proc_ipc_dointvec_minmax,
+                .extra1         = &zero,
+                .extra2         = &int_max,
+        },
+#endif
         {}
 };