new helpers: vfs_create_mount(), fc_mount()

Create a new helper, vfs_create_mount(), that creates a detached vfsmount
object from an fs_context that has a superblock attached to it.

Almost all uses will be paired with immediately preceding vfs_get_tree();
add a helper for such combination.

Switch vfs_kern_mount() to use this.

NOTE: mild behaviour change; passing NULL as 'device name' to
something like procfs will change /proc/*/mountstats - "device none"
instead on "no device".  That is consistent with /proc/mounts et.al.

[do'h - EXPORT_SYMBOL_GPL slipped in by mistake; removed]
[AV -- remove confused comment from vfs_create_mount()]
[AV -- removed the second argument]

Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/namespace.c b/fs/namespace.c
index 3f2fd7a..156771f 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -941,12 +941,59 @@ static struct mount *skip_mnt_tree(struct mount *p)
        return p;
 }
 
+/**
+ * vfs_create_mount - Create a mount for a configured superblock
+ * @fc: The configuration context with the superblock attached
+ *
+ * Create a mount to an already configured superblock.  If necessary, the
+ * caller should invoke vfs_get_tree() before calling this.
+ *
+ * Note that this does not attach the mount to anything.
+ */
+struct vfsmount *vfs_create_mount(struct fs_context *fc)
+{
+       struct mount *mnt;
+
+       if (!fc->root)
+               return ERR_PTR(-EINVAL);
+
+       mnt = alloc_vfsmnt(fc->source ?: "none");
+       if (!mnt)
+               return ERR_PTR(-ENOMEM);
+
+       if (fc->sb_flags & SB_KERNMOUNT)
+               mnt->mnt.mnt_flags = MNT_INTERNAL;
+
+       atomic_inc(&fc->root->d_sb->s_active);
+       mnt->mnt.mnt_sb         = fc->root->d_sb;
+       mnt->mnt.mnt_root       = dget(fc->root);
+       mnt->mnt_mountpoint     = mnt->mnt.mnt_root;
+       mnt->mnt_parent         = mnt;
+
+       lock_mount_hash();
+       list_add_tail(&mnt->mnt_instance, &mnt->mnt.mnt_sb->s_mounts);
+       unlock_mount_hash();
+       return &mnt->mnt;
+}
+EXPORT_SYMBOL(vfs_create_mount);
+
+struct vfsmount *fc_mount(struct fs_context *fc)
+{
+       int err = vfs_get_tree(fc);
+       if (!err) {
+               up_write(&fc->root->d_sb->s_umount);
+               return vfs_create_mount(fc);
+       }
+       return ERR_PTR(err);
+}
+EXPORT_SYMBOL(fc_mount);
+
 struct vfsmount *vfs_kern_mount(struct file_system_type *type,
                                int flags, const char *name,
                                void *data)
 {
        struct fs_context *fc;
-       struct mount *mnt;
+       struct vfsmount *mnt;
        int ret = 0;
 
        if (!type)
@@ -964,31 +1011,12 @@ struct vfsmount *vfs_kern_mount(struct file_system_type *type,
        if (!ret)
                ret = parse_monolithic_mount_data(fc, data);
        if (!ret)
-               ret = vfs_get_tree(fc);
-       if (ret) {
-               put_fs_context(fc);
-               return ERR_PTR(ret);
-       }
-       up_write(&fc->root->d_sb->s_umount);
-       mnt = alloc_vfsmnt(name);
-       if (!mnt) {
-               put_fs_context(fc);
-               return ERR_PTR(-ENOMEM);
-       }
-
-       if (flags & SB_KERNMOUNT)
-               mnt->mnt.mnt_flags = MNT_INTERNAL;
+               mnt = fc_mount(fc);
+       else
+               mnt = ERR_PTR(ret);
 
-       atomic_inc(&fc->root->d_sb->s_active);
-       mnt->mnt.mnt_root = dget(fc->root);
-       mnt->mnt.mnt_sb = fc->root->d_sb;
-       mnt->mnt_mountpoint = mnt->mnt.mnt_root;
-       mnt->mnt_parent = mnt;
-       lock_mount_hash();
-       list_add_tail(&mnt->mnt_instance, &fc->root->d_sb->s_mounts);
-       unlock_mount_hash();
        put_fs_context(fc);
-       return &mnt->mnt;
+       return mnt;
 }
 EXPORT_SYMBOL_GPL(vfs_kern_mount);
 

diff --git a/include/linux/mount.h b/include/linux/mount.h
index 037eed5..9197ddb 100644 (file)
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -21,6 +21,7 @@ struct super_block;
 struct vfsmount;
 struct dentry;
 struct mnt_namespace;
+struct fs_context;
 
 #define MNT_NOSUID     0x01
 #define MNT_NODEV      0x02
@@ -88,6 +89,8 @@ struct path;
 extern struct vfsmount *clone_private_mount(const struct path *path);
 
 struct file_system_type;
+extern struct vfsmount *fc_mount(struct fs_context *fc);
+extern struct vfsmount *vfs_create_mount(struct fs_context *fc);
 extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,
                                      int flags, const char *name,
                                      void *data);