ovl: add support for "nfs_export" configuration

Introduce the "nfs_export" config, module and mount options.

The NFS export feature depends on the "index" feature and enables two
implicit overlayfs features: "index_all" and "verify_lower".
The "index_all" feature creates an index on copy up of every file and
directory. The "verify_lower" feature uses the full index to detect
overlay filesystems inconsistencies on lookup, like redirect from
multiple upper dirs to the same lower dir.

NFS export can be enabled for non-upper mount with no index. However,
because lower layer redirects cannot be verified with the index, enabling
NFS export support on an overlay with no upper layer requires turning off
redirect follow (e.g. "redirect_dir=nofollow").

The full index may incur some overhead on mount time, especially when
verifying that lower directory file handles are not stale.

NFS export support, full index and consistency verification will be
implemented by following patches.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 1d62b1e6111a..db75955f9677 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -194,6 +194,8 @@ const struct cred *ovl_override_creds(struct super_block *sb);
 struct super_block *ovl_same_sb(struct super_block *sb);
 bool ovl_can_decode_fh(struct super_block *sb);
 struct dentry *ovl_indexdir(struct super_block *sb);
+bool ovl_index_all(struct super_block *sb);
+bool ovl_verify_lower(struct super_block *sb);
 struct ovl_entry *ovl_alloc_entry(unsigned int numlower);
 bool ovl_dentry_remote(struct dentry *dentry);
 bool ovl_dentry_weird(struct dentry *dentry);