convert do_remount_sb() to fs_context

Replace do_remount_sb() with a function, reconfigure_super(), that's
fs_context aware.  The fs_context is expected to be parameterised already
and have ->root pointing to the superblock to be reconfigured.

A legacy wrapper is provided that is intended to be called from the
fs_context ops when those appear, but for now is called directly from
reconfigure_super().  This wrapper invokes the ->remount_fs() superblock op
for the moment.  It is intended that the remount_fs() op will be phased
out.

The fs_context->purpose is set to FS_CONTEXT_FOR_RECONFIGURE to indicate
that the context is being used for reconfiguration.

do_umount_root() is provided to consolidate remount-to-R/O for umount and
emergency remount by creating a context and invoking reconfiguration.

do_remount(), do_umount() and do_emergency_remount_callback() are switched
to use the new process.

[AV -- fold UMOUNT and EMERGENCY_REMOUNT in; fixes the
umount / bug, gets rid of pointless complexity]
[AV -- set ->net_ns in all cases; nfs remount will need that]
[AV -- shift security_sb_remount() call into reconfigure_super(); the callers
that didn't do security_sb_remount() have NULL fc->security anyway, so it's
a no-op for them]

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

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/fs_context.h b/include/linux/fs_context.h
index 9805514444c9..98772f882a3e 100644
--- a/include/linux/fs_context.h
+++ b/include/linux/fs_context.h
@@ -25,6 +25,7 @@ struct user_namespace;
 
 enum fs_context_purpose {
 	FS_CONTEXT_FOR_MOUNT,		/* New superblock for explicit mount */
+	FS_CONTEXT_FOR_RECONFIGURE,	/* Superblock reconfiguration (remount) */
 };
 
 /*
@@ -57,6 +58,9 @@ struct fs_context {
  */
 extern struct fs_context *fs_context_for_mount(struct file_system_type *fs_type,
 						unsigned int sb_flags);
+extern struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,
+						unsigned int sb_flags,
+						unsigned int sb_flags_mask);
 
 extern int vfs_get_tree(struct fs_context *fc);
 extern void put_fs_context(struct fs_context *fc);