libceph: enable ceph in a non-default network namespace

Grab a reference on a network namespace of the 'rbd map' (in case of
rbd) or 'mount' (in case of ceph) process and use that to open sockets
instead of always using init_net and bailing if network namespace is
anything but init_net.  Be careful to not share struct ceph_client
instances between different namespaces and don't add any code in the
!CONFIG_NET_NS case.

This is based on a patch from Hong Zhiguo <zhiguohong@tencent.com>.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Sage Weil <sage@redhat.com>
diff --git a/net/ceph/ceph_common.c b/net/ceph/ceph_common.c
index cb7db32..f30329f 100644
--- a/net/ceph/ceph_common.c
+++ b/net/ceph/ceph_common.c
@@ -9,6 +9,7 @@
 #include <keys/ceph-type.h>
 #include <linux/module.h>
 #include <linux/mount.h>
+#include <linux/nsproxy.h>
 #include <linux/parser.h>
 #include <linux/sched.h>
 #include <linux/seq_file.h>
@@ -16,8 +17,6 @@
 #include <linux/statfs.h>
 #include <linux/string.h>
 #include <linux/vmalloc.h>
-#include <linux/nsproxy.h>
-#include <net/net_namespace.h>
 
 
 #include <linux/ceph/ceph_features.h>
@@ -131,6 +130,13 @@
 	int i;
 	int ret;
 
+	/*
+	 * Don't bother comparing options if network namespaces don't
+	 * match.
+	 */
+	if (!net_eq(current->nsproxy->net_ns, read_pnet(&client->msgr.net)))
+		return -1;
+
 	ret = memcmp(opt1, opt2, ofs);
 	if (ret)
 		return ret;
@@ -335,9 +341,6 @@
 	int err = -ENOMEM;
 	substring_t argstr[MAX_OPT_ARGS];
 
-	if (current->nsproxy->net_ns != &init_net)
-		return ERR_PTR(-EINVAL);
-
 	opt = kzalloc(sizeof(*opt), GFP_KERNEL);
 	if (!opt)
 		return ERR_PTR(-ENOMEM);
@@ -608,6 +611,7 @@
 fail_monc:
 	ceph_monc_stop(&client->monc);
 fail:
+	ceph_messenger_fini(&client->msgr);
 	kfree(client);
 	return ERR_PTR(err);
 }
@@ -621,8 +625,8 @@
 
 	/* unmount */
 	ceph_osdc_stop(&client->osdc);
-
 	ceph_monc_stop(&client->monc);
+	ceph_messenger_fini(&client->msgr);
 
 	ceph_debugfs_client_cleanup(client);