ipc/sysctl: c/r kernel.{msg_next_id,sem_next_id,shm_next_id}

These are only three left in ipc_kern_table which we haven't
checkpointed yet, I'm not sure if somebody really uses them
except criu, but to be consistent, beter not to change them
while c/r.

v3: do one sysctl_op for all xxx_next_id(as sysctl_op is quiet slow)
v4: do only one sysctl_op in ipc_sysctl_req
v5: do msg*_default only if have /proc/sys/fs/mqueue same as other
ones from fs/mqueue
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/ipc_ns.c

@@ -291,6 +291,8 @@ static void pr_info_ipc_shm(const IpcShmEntry *shm)
 	print_on_level(LOG_INFO, "size: %-10"PRIu64"\n", shm->size);
 }
 
+#define NR_MANDATORY_IPC_SYSCTLS 9
+
 static int ipc_sysctl_req(IpcVarEntry *e, int op)
 {
 	struct sysctl_req req[] = {
@@ -303,29 +305,37 @@ static int ipc_sysctl_req(IpcVarEntry *e, int op)
 		{ "kernel/shmall",		&e->shm_ctlall,		CTL_U64 },
 		{ "kernel/shmmni",		&e->shm_ctlmni,		CTL_U32 },
 		{ "kernel/shm_rmid_forced",	&e->shm_rmid_forced,	CTL_U32 },
-	};
-
-	struct sysctl_req req_mq[] = {
+		/* We have 9 mandatory sysctls above and 8 optional below */
 		{ "fs/mqueue/queues_max",	&e->mq_queues_max,	CTL_U32 },
 		{ "fs/mqueue/msg_max",		&e->mq_msg_max,		CTL_U32 },
 		{ "fs/mqueue/msgsize_max",	&e->mq_msgsize_max,	CTL_U32 },
 		{ "fs/mqueue/msg_default",	&e->mq_msg_default,	CTL_U32 },
 		{ "fs/mqueue/msgsize_default",	&e->mq_msgsize_default,	CTL_U32 },
+		{ "kernel/msg_next_id", 	&e->msg_next_id, 	CTL_U32 },
+		{ "kernel/sem_next_id", 	&e->sem_next_id, 	CTL_U32 },
+		{ "kernel/shm_next_id", 	&e->shm_next_id, 	CTL_U32 },
 	};
 
-	int ret;
-
-	ret = sysctl_op(req, ARRAY_SIZE(req), op, CLONE_NEWIPC);
-	if (ret)
-		return ret;
+	int nr = NR_MANDATORY_IPC_SYSCTLS;
 
-	if (access("/proc/sys/fs/mqueue", X_OK)) {
+	/* Skip sysctls which can't be set or haven't existed on dump */
+	if (access("/proc/sys/fs/mqueue", X_OK))
 		pr_info("Mqueue sysctls are missing\n");
-		return 0;
+	else {
+		nr += 3;
+		if (e->has_mq_msg_default) {
+			req[nr++] = req[12];
+			req[nr++] = req[13];
+		}
 	}
+	if (e->has_msg_next_id)
+		req[nr++] = req[14];
+	if (e->has_sem_next_id)
+		req[nr++] = req[15];
+	if (e->has_shm_next_id)
+		req[nr++] = req[16];
 
-	return sysctl_op(req_mq, ARRAY_SIZE(req_mq) - (e->has_mq_msg_default ? 0 : 2),
-	                 op, CLONE_NEWIPC);
+	return sysctl_op(req, nr, op, CLONE_NEWIPC);
 }
 
 /*
@@ -421,6 +431,9 @@ static int dump_ipc_var(struct cr_img *img)
 		goto err;
 	var.has_mq_msg_default = true;
 	var.has_mq_msgsize_default = true;
+	var.has_msg_next_id = true;
+	var.has_sem_next_id = true;
+	var.has_shm_next_id = true;
 
 	ret = ipc_sysctl_req(&var, CTL_READ);
 	if (ret < 0) {
@@ -428,6 +441,17 @@ static int dump_ipc_var(struct cr_img *img)
 		goto err;
 	}
 
+	/*
+	 * One can not write to msg_next_xxx sysctls -1,
+	 * which is their initial value
+	 */
+	if (var.msg_next_id == -1)
+		var.has_msg_next_id = false;
+	if (var.sem_next_id == -1)
+		var.has_sem_next_id = false;
+	if (var.shm_next_id == -1)
+		var.has_shm_next_id = false;
+
 	ret = pb_write_one(img, &var, PB_IPC_VAR);
 	if (ret < 0) {
 		pr_err("Failed to write IPC variables\n");

images/ipc-var.proto

@@ -15,4 +15,7 @@ message ipc_var_entry {
 	required uint32			mq_msgsize_max		= 12;
 	optional uint32			mq_msg_default		= 13;
 	optional uint32			mq_msgsize_default	= 14;
+	optional uint32			msg_next_id		= 15;
+	optional uint32			sem_next_id		= 16;
+	optional uint32			shm_next_id		= 17;
 }