On Thu, 9 Sep 2010 13:27:38 -0400
Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>
> On Sep 6, 2010, at 9:12 PM, Neil Brown wrote:
>
> > On Tue, 31 Aug 2010 17:21:31 -0400
> > Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
> >
> >> The logic that manages negotiating NFS version and protocol settings
> >> is getting more complex over time, so let's split this out of
> >> nfs_try_mount().
> >>
> >> This should make Bruce a little happier, as it eliminates the silent
> >> switch case fall through in nfs_try_mount(). And it should help Neil
> >> fix some bugs he's found in this logic.
> >
> > Hi Chuck,
> > thanks for these..
> > One question....
> >
> > .....
> >> +{
> >> + int result;
> >> +
> >> + /*
> >> + * Before 2.6.32, the kernel NFS client didn't support
> >> + * "-t nfs vers=4" mounts, so NFS version 4 cannot be
> >> + * included when autonegotiating while running on
> >> + * those kernels.
> >> + */
> >> + if (linux_version_code() <= MAKE_VERSION(2, 6, 31))
> >> + goto fall_back;
> >> +
> >> + errno = 0;
> >> + result = nfs_try_mount_v4(mi);
> >> + switch (errno) {
> >
> > Should we not have e.g.
> >
> > if (result)
> > return result;
> >
> > before the switch(errno)?? Typically errno is 'undefined' in no error is
> > reported.
> >
> > I realise the current code doesn't have that test either, but I still think
> > it is wrong not to.
>
> We have
>
> errno = 0;
>
> just before the nfs_try_mount_v4(mi); call. This defines the value of errno even if nothing in nfs_try_mount_v4() sets it.
True, but what if something in nfs_try_mount_v4 does set it, but success is
finally returned? That is certainly possible if mi has multiple addresses
and the first is unreachable.
I think you must *never* test errno unless the most recent call reported an
error.
>
> Perhaps that violates Bruce's "too subtle" rule and I should replace it with your suggested post-call check?
He's like a guardian angel sitting on you shoulder whispering "too subtle"
all the time :-) Definitely true this time.
Thanks,
NeilBrown
>
> > Thanks
> > NeilBrown
> >
> >
> >
> >> + case EPROTONOSUPPORT:
> >> + /* A clear indication that the server or our
> >> + * client does not support NFS version 4. */
> >> + goto fall_back;
> >> + case ENOENT:
> >> + /* Legacy Linux servers don't export an NFS
> >> + * version 4 pseudoroot. */
> >> + goto fall_back;
> >> + case EPERM:
> >> + /* Linux servers prior to 2.6.25 may return
> >> + * EPERM when NFS version 4 is not supported. */
> >> + goto fall_back;
> >> + default:
> >> + return result;
> >> + }
> >> +
> >> +fall_back:
> >> + return nfs_try_mount_v3v2(mi);
> >> +}
> >> +
> >> +/*
> >> * This is a single pass through the fg/bg loop.
> >> *
> >> * Returns TRUE if successful, otherwise FALSE.
> >> @@ -758,20 +801,8 @@ static int nfs_try_mount(struct nfsmount_info *mi)
> >>
> >> switch (mi->version) {
> >> case 0:
> >> - if (linux_version_code() > MAKE_VERSION(2, 6, 31)) {
> >> - errno = 0;
> >> - result = nfs_try_mount_v4(mi);
> >> - if (errno != EPROTONOSUPPORT) {
> >> - /*
> >> - * To deal with legacy Linux servers that don't
> >> - * automatically export a pseudo root, retry
> >> - * ENOENT errors using version 3. And for
> >> - * Linux servers prior to 2.6.25, retry EPERM
> >> - */
> >> - if (errno != ENOENT && errno != EPERM)
> >> - break;
> >> - }
> >> - }
> >> + result = nfs_autonegotiate(mi);
> >> + break;
> >> case 2:
> >> case 3:
> >> result = nfs_try_mount_v3v2(mi);
> >
>
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