When all layers are on the same underlying filesystem, let stat(2)
return st_dev/st_ino values of the copy up origin inode if it is
known.
This results in constant st_ino/st_dev representation of files in an
overlay mount before and after copy up.
When the underlying filesystem support NFS exportfs, the result is also
persistent st_ino/st_dev representation before and after mount cycle.
Lower hardlinks are broken on copy up to differnt upper files, so we
cannot use the lower origin st_ino for those different files, even for
the same fs case.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/overlayfs/inode.c | 27 ++++++++++++++++++++++++++-
1 file changed, 26 insertions(+), 1 deletion(-)
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 17b8418..9c0c4e1 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -69,7 +69,32 @@ static int ovl_getattr(const struct path *path, struct kstat *stat,
old_cred = ovl_override_creds(dentry->d_sb);
err = vfs_getattr(&realpath, stat, request_mask, flags);
revert_creds(old_cred);
- return err;
+ if (err)
+ return err;
+
+ /*
+ * When all layers are on the same fs, we use st_ino of the copy up
+ * origin, if we know it.
+ * This guaranties constant st_dev/st_ino across copy up.
+ *
+ * When redirect_fh is enabled, this also guaranties persistent
+ * st_ino/st_dev across mount cycle.
+ */
+ if (ovl_same_sb(dentry->d_sb)) {
+ struct dentry *lower = ovl_dentry_lower(dentry);
+
+ /*
+ * Lower hardlinks are broken on copy up to differnt upper
+ * files, so we cannot use the lower origin st_ino for those
+ * different files, even for the same fs case.
+ */
+ if (lower && lower->d_inode->i_nlink == 1) {
+ stat->dev = lower->d_sb->s_dev;
+ stat->ino = lower->d_inode->i_ino;
+ }
+ }
+
+ return 0;
}
int ovl_permission(struct inode *inode, int mask)
--
2.7.4
