Re: [RFC PATCH] mount.nfs: skip option validation on remount

[Benjamin Coddington <bcodding@redhat.com>]

On Wed, 6 Apr 2016, Chuck Lever wrote:
>
> > On Apr 6, 2016, at 6:41 AM, Benjamin Coddington <bcodding@redhat.com> wrote:
> >
> > I'm not exactly sure this is the safest thing to do since you can pass
> > -oremount on the first mount and skip option validation.  Maybe someone with
> > better insight into the mount paths could comment.  Does mount need some
> > refactoring?  Its logic seems arcane.. and I think there is a lot of dead
> > code.
>
> It's arcane because NFS mounting has a lot of corner cases
> that have evolved over the years. If you have an example of
> dead code, can you post it?

Absolutely.  I don't have it ready right now, but I do remember coming across
some sections several times and wondering how they could be used.

I need to do a better job of posting when I find things instead of putting
them off and forgetting about them.

> > This is very quick attempt to fix
> > https://bugzilla.redhat.com/show_bug.cgi?id=1313550
>
> "You are not authorized to access bug #1313550."

Sorry.  I've just tried to fix that and I cannot.  The basic info there is
that kdump always tries to remount,rw a target.. and that is breaking on
NFS.  The bug doesn't really provide anything more useful to the discussion
other than maybe help Steved find the original problem.

> I'm guessing you want to use the existing addr= option on a
> remount in case the DNS resolution returns a different address.

Right.

> I'm uncertain why a remount should succeed in this case: if
> the server has a different IP address, how was the mount working
> at all?

If the server has multiple A or AAAA records, and the the results are
returned round-robin style, we can end up with a different address for
the server.

Ben

> > 8<-------------------------------------------------------------------------
> >
> > A remount might fail if name resolution returns a different server address
> > for the mount.  Since we've already validated the options the first time,
> > skip validation if remounting.
> >
> > Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
> > ---
> > utils/mount/stropts.c |    6 +++---
> > 1 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/utils/mount/stropts.c b/utils/mount/stropts.c
> > index 86829a9..9383bb4 100644
> > --- a/utils/mount/stropts.c
> > +++ b/utils/mount/stropts.c
> > @@ -1090,15 +1090,15 @@ static const char *nfs_background_opttbl[] = {
> >
> > static int nfsmount_start(struct nfsmount_info *mi)
> > {
> > -	if (!nfs_validate_options(mi))
> > -		return EX_FAIL;
> > -
> > 	/*
> > 	 * Avoid retry and negotiation logic when remounting
> > 	 */
> > 	if (mi->flags & MS_REMOUNT)
> > 		return nfs_remount(mi);
> >
> > +	if (!nfs_validate_options(mi))
> > +		return EX_FAIL;
> > +
> > 	if (po_rightmost(mi->options, nfs_background_opttbl) == 0)
> > 		return nfsmount_bg(mi);
> > 	else
> > --
> > 1.7.1
> >
> > --
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>
> --
> Chuck Lever