On Wed, Jun 21, 2017 at 3:28 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> With inodes index enabled, an overlay inode nlink counts the union of upper
> and non-covered lower hardlinks. During the lifetime of a non-pure upper
> inode, the following nlink modifying operations can happen:
>
> 1. Lower hardlink copy up
> 2. Upper hardlink created, unlinked or renamed over
> 3. Lower hardlink whiteout or renamed over
>
> For the first, copy up case, the union nlink does not change, whether the
> operation succeeds or fails, but the upper inode nlink may change.
> Therefore, before copy up, we store the union nlink value relative to the
> lower inode nlink in the index inode xattr trusted.overlay.nlink.
>
> For the second, upper hardlink case, the union nlink should be incremented
> or decremented IFF the operation succeeds, aligned with nlink change of the
> upper inode. Therefore, before link/unlink/rename, we store the union nlink
> value relative to the upper inode nlink in the index inode.
>
> For the last, lower cover up case, we simplify things by preceding the
> whiteout or cover up with copy up. This makes sure that there is an index
> upper inode where the nlink xattr can be stored before the copied up upper
> entry is unlink.
>
> Return the overlay inode nlinks for indexed upper inodes on stat(2).
>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> fs/overlayfs/copy_up.c | 88 +++++++++++++++++++++++++++-------------
> fs/overlayfs/dir.c | 80 +++++++++++++++++++++++++++++++++++-
> fs/overlayfs/inode.c | 103 ++++++++++++++++++++++++++++++++++++++++++++++-
> fs/overlayfs/namei.c | 2 +-
> fs/overlayfs/overlayfs.h | 6 ++-
> 5 files changed, 245 insertions(+), 34 deletions(-)
>
...
> +
> +static unsigned int ovl_get_nlink(struct ovl_inode_info *info,
> + struct dentry *index, unsigned int real_nlink)
> +{
> + struct ovl_nlink onlink;
> + __s32 nlink_add = 0;
> + int res;
> +
> + if (!index || !index->d_inode)
> + return real_nlink;
> +
> + res = vfs_getxattr(index, OVL_XATTR_NLINK, &onlink, sizeof(onlink));
> + if (res < sizeof(onlink))
> + goto fail;
> +
I tested cleanup of orphans due to missing nlink xattr.
Apparently, ((int)-ENODATAT < sizeof(onlink)) is false..
if (res != sizeof(onlink)) works better
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