Messages in this thread | | | Date | Fri, 5 Jun 2015 01:07:15 +0100 | From | Al Viro <> | Subject | Re: [PATCH 2/2] ovl: allow distributed fs as lower layer |
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On Thu, Jun 04, 2015 at 03:29:46PM +0200, Miklos Szeredi wrote: > From: Miklos Szeredi <mszeredi@suse.cz> > > 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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