nfs-utils: Something is wrong in is_vers4()

[NeilBrown <neilb@xxxxxxx>]

in nfs-utils, in utils/mount/mount_libmount.c there is a function

 is_vers4()

which
 /* returns: error = -1, success = 0 , unknown = 1 */

which seems odd to me... I would have chosen '1' for success (it is vers 4),
0 for failure (not vers 4), and maybe -1 for error (something went wrong).

This is used as follows:
			switch (is_vers4(cxt)) {
			case 0:
				/* We ignore the error from nfs_umount23.
				 * If the actual umount succeeds (in del_mtab),
				 * we don't want to signal an error, as that
				 * could cause /sbin/mount to retry!
				 */
				nfs_umount23(mnt_context_get_source(cxt), opts);
				break;
			case 1:			/* unknown */
				break;
			default:		/* error */
				goto err;
			}

so in the '0' (success, it is vers4) case we do nfs_umount23.  Odd.
In the '1' (unknown, so presumably vers2 or 3) we don't.  Ever.  Very odd.

So we don't currently send MOUNT_UMNT requests for v2 or v3.
We don't for v4 either because nfs_umount_do_umnt contains:

	/* Skip UMNT call for vers=4 mounts */
	if (nfs_pmap.pm_vers == 4)
		return EX_SUCCESS;

so maybe is_vers4 isn't needed?

Looks like something needs to be fixed here but I'm not entirely sure what.
Karel??

BTW Steve, Karel's "[PATCH] umount.nfs: ignore non-nfs filesystems"
which appears in email:

From: Karel Zak <kzak@xxxxxxxxxx>
To: NeilBrown <neilb@xxxxxxx>
Cc: Steve Dickson <SteveD@xxxxxxxxxx>, NFS <linux-nfs@xxxxxxxxxxxxxxx>
Subject: Re: [PATCH] umount.nfs: restore correct error status when umount fails.
Date: Thu, 12 Jul 2012 18:44:20 +0200

hasn't been applied, but probably should be.

Thanks,
NeilBrown

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