On Wed, Jun 14, 2017 at 10:26 AM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> With inodes index feature, all lower and upper hardlinks point to
> the same overlay inode. However, when a lower hardlink is accessed
> for read operation, the real inode operated on is not the same inode
> as the real inode for read operation on an upper hardlink.
>
> When lookup finds a lower hardlink, which is already indexed by
> an earlier upper hardlink copy up, call ovl_copy_up() to link the
> indexed upper on top of the lower hardlink and then operate on the
> upper real inode to avoid this inconsistency.
>
> Invalidate a lower indexed dentry on dcache lookup, so ovl_lookup()
> is called to perform the index link up.
>
> The following test demonstrates the upper/lower hardlinks inconsistency:
>
> $ echo -n a > /lower/foo
> $ ln /lower/foo /lower/bar
> $ cd /mnt
> $ echo -n b >> foo
> $ tail foo bar # foo is indexed upper, bar is indexed lower
> ==> foo <==
> ab
> ==> bar <==
> a
>
> $ echo -n c >> bar
> $ tail foo bar # both aliases are indexed upper
> ==> foo <==
> abc
> ==> bar <==
> abc
>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> fs/overlayfs/namei.c | 11 ++++++++++-
> fs/overlayfs/super.c | 32 +++++++++++++++++++++++++++-----
> 2 files changed, 37 insertions(+), 6 deletions(-)
>
> +
> +static const struct dentry_operations ovl_dentry_operations = {
> + .d_release = ovl_dentry_release,
> + .d_real = ovl_d_real,
> + .d_revalidate = ovl_dentry_indexed_revalidate,
> +};
> +
> static int ovl_dentry_revalidate(struct dentry *dentry, unsigned int flags)
> {
ovl_dentry_indexed_revalidate() should also be checked within this variant.
Will fix for next posting.
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