mount: Dump external bind-mounts with plugins

External bind mounts are those with source sitting outside of the
current FS view. Such are detected in validate_mounts(), so we
just go ahead and call plugins.

The plugin is provided with the mountpoint to decide whether it's
his or not (what else does the guy need?) and an ID with this it
can identify the mountpoint in /proc. The same ID will be used at
restore time to find the needed restore info.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/criu-plugin.h

@@ -32,6 +32,8 @@ typedef int (cr_plugin_restore_unix_sk_t)(int id);
 typedef int (cr_plugin_dump_file_t)(int fd, int id);
 typedef int (cr_plugin_restore_file_t)(int id);
 
+typedef int (cr_plugin_dump_ext_mount_t)(char *mountpoint, int id);
+
 /* Public API */
 extern int criu_get_image_dir(void);
 

include/plugin.h

@@ -14,4 +14,6 @@ int cr_plugin_restore_unix_sk(int id);
 int cr_plugin_dump_file(int fd, int id);
 int cr_plugin_restore_file(int id);
 
+int cr_plugin_dump_ext_mount(char *mountpoint, int id);
+
 #endif

include/proc_parse.h

@@ -112,6 +112,7 @@ struct mount_info {
 	char		*source;
 	char		*options;
 	bool		mounted;
+	bool		need_plugin;
 	struct mount_info *next;
 
 	/* tree linkage */

mount.c

@@ -17,6 +17,7 @@
 #include "util.h"
 #include "util-pie.h"
 #include "log.h"
+#include "plugin.h"
 #include "mount.h"
 #include "pstree.h"
 #include "proc_parse.h"
@@ -42,7 +43,7 @@ static DIR *open_mountpoint(struct mount_info *pm);
 static int close_mountpoint(DIR *dfd);
 
 static struct mount_info *mnt_build_tree(struct mount_info *list);
-static int validate_mounts(struct mount_info *info);
+static int validate_mounts(struct mount_info *info, bool call_plugins);
 
 static inline int is_root(char *p)
 {
@@ -294,7 +295,7 @@ static void mnt_tree_show(struct mount_info *tree, int off)
 	pr_info("%*s<--\n", off, "");
 }
 
-static int validate_mounts(struct mount_info *info)
+static int validate_mounts(struct mount_info *info, bool call_plugins)
 {
 	struct mount_info *m, *t;
 
@@ -325,9 +326,19 @@ static int validate_mounts(struct mount_info *info)
 					break;
 			}
 			if (&t->mnt_bind == &m->mnt_bind) {
-				pr_err("%d:%s doesn't have a proper root mount\n",
-					m->mnt_id, m->mountpoint);
-				return -1;
+				int ret = -ENOTSUP;
+
+				if (call_plugins) {
+					ret = cr_plugin_dump_ext_mount(m->mountpoint, m->mnt_id);
+					if (ret == 0)
+						m->need_plugin = true;
+				}
+				if (ret < 0) {
+					if (ret == -ENOTSUP)
+						pr_err("%d:%s doesn't have a proper root mount\n",
+								m->mnt_id, m->mountpoint);
+					return -1;
+				}
 			}
 		}
 
@@ -716,7 +727,7 @@ static int dump_one_mountpoint(struct mount_info *pm, int fd)
 		return -1;
 	}
 
-	if (pm->fstype->dump && pm->fstype->dump(pm))
+	if (!pm->need_plugin && pm->fstype->dump && pm->fstype->dump(pm))
 		return -1;
 
 	me.mnt_id		= pm->mnt_id;
@@ -731,6 +742,10 @@ static int dump_one_mountpoint(struct mount_info *pm, int fd)
 	me.has_shared_id	= true;
 	me.master_id		= pm->master_id;
 	me.has_master_id	= true;
+	if (pm->need_plugin) {
+		me.has_with_plugin = true;
+		me.with_plugin = true;
+	}
 
 	if (pb_write_one(fd, &me, PB_MNT))
 		return -1;
@@ -756,7 +771,7 @@ int dump_mnt_ns(int ns_pid, int ns_id)
 	if (mnt_build_tree(pm) == NULL)
 		goto err;
 
-	if (validate_mounts(pm))
+	if (validate_mounts(pm, true))
 		goto err;
 
 	pr_info("Dumping mountpoints\n");
@@ -1297,7 +1312,7 @@ static int populate_mnt_ns(int ns_pid, struct mount_info *mis)
 	if (!pms)
 		return -1;
 
-	if (validate_mounts(pms))
+	if (validate_mounts(pms, false))
 		return -1;
 
 	mntinfo_tree = pms;

plugin.c

@@ -19,6 +19,7 @@ struct cr_plugin_entry {
 		cr_plugin_restore_unix_sk_t *cr_plugin_restore_unix_sk;
 		cr_plugin_dump_file_t *cr_plugin_dump_file;
 		cr_plugin_restore_file_t *cr_plugin_restore_file;
+		cr_plugin_dump_ext_mount_t *cr_plugin_dump_ext_mount;
 	};
 
 	struct cr_plugin_entry *next;
@@ -31,6 +32,7 @@ struct cr_plugins {
 	struct cr_plugin_entry *cr_plugin_restore_unix_sk;
 	struct cr_plugin_entry *cr_plugin_dump_file;
 	struct cr_plugin_entry *cr_plugin_restore_file;
+	struct cr_plugin_entry *cr_plugin_dump_ext_mount;
 };
 
 struct cr_plugins cr_plugins;
@@ -87,6 +89,11 @@ int cr_plugin_restore_file(int id)
 	return run_plugin_funcs(cr_plugin_restore_file, id);
 }
 
+int cr_plugin_dump_ext_mount(char *mountpoint, int id)
+{
+	return run_plugin_funcs(cr_plugin_dump_ext_mount, mountpoint, id);
+}
+
 static int cr_lib_load(char *path)
 {
 	struct cr_plugin_entry *ce;
@@ -106,6 +113,8 @@ static int cr_lib_load(char *path)
 	add_plugin_func(cr_plugin_dump_file);
 	add_plugin_func(cr_plugin_restore_file);
 
+	add_plugin_func(cr_plugin_dump_ext_mount);
+
 	ce = NULL;
 	f_fini = dlsym(h, "cr_plugin_fini");
 	if (f_fini) {

protobuf/mnt.proto

@@ -23,4 +23,6 @@ message mnt_entry {
 
 	optional uint32		shared_id		= 10;
 	optional uint32		master_id		= 11;
+
+	optional bool		with_plugin		= 12;
 }