On Thu, Jun 04, 2015 at 03:29:46PM +0200, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@xxxxxxx>
>
> Allow filesystems with .d_revalidate as lower layer(s), but not as upper
> layer.
>
> For local filesystems the rule was that modifications on the layers
> directly while being part of the overlay results in undefined behavior.
>
> This can easily be extended to distributed filesystems: we assume the tree
> used as lower layer is static, which means ->d_revalidate() should always
> return "1". If that is not the case, return -ESTALE, don't try to work
> around the modification.
Umm... Cosmetical point is that this
> +static bool ovl_remote(struct dentry *root)
> +{
> + const struct dentry_operations *dop = root->d_op;
> +
> + return dop && (dop->d_revalidate || dop->d_weak_revalidate);
> +}
is better done as
root->d_flags & (DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE)
More interesting question is whether anything in the system relies on
existing behaviour that follows ->d_revalidate() returning 0. Have you
tried to mount e.g. procfs as underlying layer and torture it for a while?
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