[CRIU] [PATCH RFC 2/2] mount: "get fs type by mount id" helper introduced

[Stanislav Kinsburskiy]

This helper takes mount id, discovers struct mountinfo and takes fs magic from
fstype object, is present. Returns error otherwise.

Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
---
 files.c              |    5 +++--
 include/mount.h      |    1 +
 include/proc_parse.h |    1 +
 mount.c              |   24 +++++++++++++++++++++---
 4 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/files.c b/files.c
index 3a96985..04fd9eb 100644
--- a/files.c
+++ b/files.c
@@ -280,8 +280,9 @@ static int fill_fd_params(struct parasite_ctl *ctl, int fd, int lfd,
 	if (parse_fdinfo_pid(ctl->pid.real, fd, FD_TYPES__UND, NULL, &fdinfo))
 		return -1;
 
-	if (get_fstype_by_fd(lfd, &fs_type))
-		return -1;
+	if (get_fstype_by_mntid(fdinfo.mnt_id, &fs_type))
+		if (get_fstype_by_fd(lfd, &fs_type))
+			return -1;
 
 	p->fs_type	= fs_type;
 	p->ctl		= ctl;
diff --git a/include/mount.h b/include/mount.h
index 4989b41..eb9546f 100644
--- a/include/mount.h
+++ b/include/mount.h
@@ -128,5 +128,6 @@ extern void cleanup_mnt_ns(void);
 
 extern int get_fstype_by_fd(int fd, unsigned int *type);
 extern int get_fstype_by_path(const char *path, unsigned int *type);
+extern int get_fstype_by_mntid(unsigned int id, unsigned int *type);
 
 #endif /* __CR_MOUNT_H__ */
diff --git a/include/proc_parse.h b/include/proc_parse.h
index 9e932db..8521eff 100644
--- a/include/proc_parse.h
+++ b/include/proc_parse.h
@@ -117,6 +117,7 @@ struct fstype {
 	int (*parse)(struct mount_info *pm);
 	bool (*can_mount)(struct mount_info *pm);
 	mount_fn_t mount;
+	unsigned int fs_magic;
 };
 
 struct vm_area_list;
diff --git a/mount.c b/mount.c
index f5d8773..355cd88 100644
--- a/mount.c
+++ b/mount.c
@@ -237,6 +237,21 @@ int get_fstype_by_path(const char *path, unsigned int *type)
 	return 0;
 }
 
+int get_fstype_by_mntid(unsigned int id, unsigned int *type)
+{
+	struct mount_info *m;
+
+	m = lookup_mnt_id(id);
+	if (!m)
+		return -EINVAL;
+
+	if (m->fstype->fs_magic == 0)
+		return -ENOENT;
+
+	*type = m->fstype->fs_magic;
+	return 0;
+}
+
 struct mount_info *lookup_mnt_sdev(unsigned int s_dev)
 {
 	struct mount_info *m;
@@ -1810,11 +1825,13 @@ static struct fstype fstypes[32] = {
 		.code = FSTYPE__NFS,
 		.mount = nfs_mount,
 		.can_mount = nfs_can_mount,
+		.fs_magic = NFS_SUPER_MAGIC,
 	}, {
 		.name = "nfs4",
 		.code = FSTYPE__NFS4,
 		.mount = nfs_mount,
 		.can_mount = nfs_can_mount,
+		.fs_magic = NFS_SUPER_MAGIC,
 	}
 };
 
@@ -2631,10 +2648,11 @@ static int do_mount_one(struct mount_info *mi)
 		return -1;
 
 	if (mi->fstype->code == FSTYPE__UNSUPPORTED) {
-		unsigned int fs_type;
+		unsigned int fstype = mi->fstype->fs_magic;
 
-		if (get_fstype_by_path(mi->mountpoint, &fs_type))
-			return -1;
+		if (fstype == 0)
+			if (get_fstype_by_path(mi->mountpoint, &fstype))
+				return -1;
 
 		if (fstype == BTRFS_SUPER_MAGIC)
 			mi->fstype = find_fstype_by_name("btrfs");