[RFC PATCH 54/68] vfs: Add a single-or-reconfig keying to vfs_get_super()

[David Howells]

Add an additional keying mode to vfs_get_super() to indicate that only a
single superblock should exist in the system, and that, if it does, further
mounts should invoke reconfiguration upon it.

This allows mount_single() to be replaced.

Signed-off-by: David Howells <dhowe...@redhat.com>
---

 fs/super.c                 |   24 +++++++++++++++++-------
 include/linux/fs_context.h |    1 +
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 6cb57ad31e6f..60c9caeae3c7 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1175,9 +1175,11 @@ int vfs_get_super(struct fs_context *fc,
 {
        int (*test)(struct super_block *, struct fs_context *);
        struct super_block *sb;
+       int err;
 
        switch (keying) {
        case vfs_get_single_super:
+       case vfs_get_single_reconf_super:
                test = test_single_super;
                break;
        case vfs_get_keyed_super:
@@ -1195,18 +1197,26 @@ int vfs_get_super(struct fs_context *fc,
                return PTR_ERR(sb);
 
        if (!sb->s_root) {
-               int err = fill_super(sb, fc);
-               if (err) {
-                       deactivate_locked_super(sb);
-                       return err;
-               }
+               err = fill_super(sb, fc);
+               if (err)
+                       goto error;
 
                sb->s_flags |= SB_ACTIVE;
+               fc->root = dget(sb->s_root);
+       } else {
+               fc->root = dget(sb->s_root);
+               if (keying == vfs_get_single_reconf_super) {
+                       err = reconfigure_super(fc);
+                       if (err < 0)
+                               goto error;
+               }
        }
 
-       BUG_ON(fc->root);
-       fc->root = dget(sb->s_root);
        return 0;
+
+error:
+       deactivate_locked_super(sb);
+       return err;
 }
 EXPORT_SYMBOL(vfs_get_super);
 
diff --git a/include/linux/fs_context.h b/include/linux/fs_context.h
index 7c7eefb35cc3..3b1da9b2db91 100644
--- a/include/linux/fs_context.h
+++ b/include/linux/fs_context.h
@@ -138,6 +138,7 @@ extern int vfs_init_pseudo_fs_context(struct fs_context *fc,
  */
 enum vfs_get_super_keying {
        vfs_get_single_super,   /* Only one such superblock may exist */
+       vfs_get_single_reconf_super, /* As above, but reconfigure if it exists 
*/
        vfs_get_keyed_super,    /* Superblocks with different s_fs_info keys 
may exist */
        vfs_get_independent_super, /* Multiple independent superblocks may 
exist */
 };