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 8:47 AM, Chuck Lever <chuck.lever@oracle.com> wrote:
> >
> >>
> >> On Apr 6, 2016, at 8:24 AM, Benjamin Coddington <bcodding@redhat.com> wrote:
> >>
> >> 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.
> >
> > Always breaking? Or just in the case where the server has
> > multiple homes?
> >
> >
> >> 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.
> >
> > I agree that a second DNS resolution here is probably not
> > helpful or needed. Still, multi-home NFS seems like a crap
> > shoot to begin with. Maybe I'm just not awake yet.
>
> I should clarify: I mean round-robin here, not multi-home.
>
> Is this only a problem when the server has an A and an
> AAAA address, and there's no "proto=" specified?

In my testing it was a problem when returning multiple A records
round-robin.  I think the same thing would be true of multiple AAAA records.

I don't think this problem exists with an A record and an AAAA record
because getaddrinfo doesn't group them - they are different families.

Ben

> > But I think you do need to validate mount options on a
> > remount: otherwise you can pass "-o remount,garbage". Or
> > did I misunderstand?
> >
> >
> >> 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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> >>>> the body of a message to majordomo@vger.kernel.org
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> >>>
> >>> --
> >>> Chuck Lever
> >
> > --
> > Chuck Lever
> >
> >
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
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>
> --
> Chuck Lever
>
>
>
>