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Subject[RFC PATCH 54/68] vfs: Add a single-or-reconfig keying to vfs_get_super()
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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 <dhowells@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 */
};
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