mqueue: separate mqueue default value from maximum value

Commit b231cca4381e ("message queues: increase range limits") changed
mqueue default value when attr parameter is specified NULL from hard
coded value to fs.mqueue.{msg,msgsize}_max sysctl value.

This made large side effect.  When user need to use two mqueue
applications 1) using !NULL attr parameter and it require big message
size and 2) using NULL attr parameter and only need small size message,
app (1) require to raise fs.mqueue.msgsize_max and app (2) consume large
memory size even though it doesn't need.

Doug Ledford propsed to switch back it to static hard coded value.
However it also has a compatibility problem.  Some applications might
started depend on the default value is tunable.

The solution is to separate default value from maximum value.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
Acked-by: Doug Ledford <dledford@redhat.com>
Acked-by: Joe Korty <joe.korty@ccur.com>
Cc: Amerigo Wang <amwang@redhat.com>
Acked-by: Serge E. Hallyn <serue@us.ibm.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 33 insertions, 3 deletions

diff --git a/Documentation/sysctl/fs.txt b/Documentation/sysctl/fs.txt
index 88fd7f5..13d6166 100644
--- a/Documentation/sysctl/fs.txt
+++ b/Documentation/sysctl/fs.txt
@@ -225,6 +225,13 @@ a queue must be less or equal then msg_max.
 maximum  message size value (it is every  message queue's attribute set during
 its creation).
 
+/proc/sys/fs/mqueue/msg_default is  a read/write  file for setting/getting the
+default number of messages in a queue value if attr parameter of mq_open(2) is
+NULL. If it exceed msg_max, the default value is initialized msg_max.
+
+/proc/sys/fs/mqueue/msgsize_default is a read/write file for setting/getting
+the default message size value if attr parameter of mq_open(2) is NULL. If it
+exceed msgsize_max, the default value is initialized msgsize_max.
 
 4. /proc/sys/fs/epoll - Configuration options for the epoll interface
 --------------------------------------------------------
diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
index 2488535..5499c92 100644
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -62,6 +62,8 @@ struct ipc_namespace {
 	unsigned int    mq_queues_max;   /* initialized to DFLT_QUEUESMAX */
 	unsigned int    mq_msg_max;      /* initialized to DFLT_MSGMAX */
 	unsigned int    mq_msgsize_max;  /* initialized to DFLT_MSGSIZEMAX */
+	unsigned int    mq_msg_default;
+	unsigned int    mq_msgsize_default;
 
 	/* user_ns which owns the ipc ns */
 	struct user_namespace *user_ns;
diff --git a/ipc/mq_sysctl.c b/ipc/mq_sysctl.c
index e22336a..383d638 100644
--- a/ipc/mq_sysctl.c
+++ b/ipc/mq_sysctl.c
@@ -73,6 +73,24 @@ static ctl_table mq_sysctls[] = {
 		.extra1		= &msg_maxsize_limit_min,
 		.extra2		= &msg_maxsize_limit_max,
 	},
+	{
+		.procname	= "msg_default",
+		.data		= &init_ipc_ns.mq_msg_default,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_mq_dointvec_minmax,
+		.extra1		= &msg_max_limit_min,
+		.extra2		= &msg_max_limit_max,
+	},
+	{
+		.procname	= "msgsize_default",
+		.data		= &init_ipc_ns.mq_msgsize_default,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_mq_dointvec_minmax,
+		.extra1		= &msg_maxsize_limit_min,
+		.extra2		= &msg_maxsize_limit_max,
+	},
 	{}
 };
 
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 6828e2c..609d53f 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -145,9 +145,10 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
 		info->qsize = 0;
 		info->user = NULL;	/* set when all is ok */
 		memset(&info->attr, 0, sizeof(info->attr));
-		info->attr.mq_maxmsg = min(ipc_ns->mq_msg_max, DFLT_MSG);
-		info->attr.mq_msgsize =
-			min(ipc_ns->mq_msgsize_max, DFLT_MSGSIZE);
+		info->attr.mq_maxmsg = min(ipc_ns->mq_msg_max,
+					   ipc_ns->mq_msg_default);
+		info->attr.mq_msgsize = min(ipc_ns->mq_msgsize_max,
+					    ipc_ns->mq_msgsize_default);
 		if (attr) {
 			info->attr.mq_maxmsg = attr->mq_maxmsg;
 			info->attr.mq_msgsize = attr->mq_msgsize;
@@ -1261,6 +1262,8 @@ int mq_init_ns(struct ipc_namespace *ns)
 	ns->mq_queues_max    = DFLT_QUEUESMAX;
 	ns->mq_msg_max       = DFLT_MSGMAX;
 	ns->mq_msgsize_max   = DFLT_MSGSIZEMAX;
+	ns->mq_msg_default   = DFLT_MSG;
+	ns->mq_msgsize_default  = DFLT_MSGSIZE;
 
 	ns->mq_mnt = kern_mount_data(&mqueue_fs_type, ns);
 	if (IS_ERR(ns->mq_mnt)) {