Let zfs diff be more permissive.

In the current world, `zfs diff` will die on certain kinds of errors
that come up on ordinary, not-mangled filesystems - like EINVAL,
which can come from a file with multiple hardlinks having the one
whose name is referenced deleted.

Since they don't appear to indicate the snapshot is mangled in any
way, let's relax about ENOENT and EINVAL - still print an error,
but don't immediately abort when we encounter them.

Signed-off-by: Rich Ercolani <rincebrain@gmail.com>

lib/libzfs/libzfs_diff.c

@@ -243,6 +243,7 @@ write_inuse_diffs_one(FILE *fp, differ_info_t *di, uint64_t dobj)
 	struct zfs_stat fsb, tsb;
 	mode_t fmode, tmode;
 	char fobjname[MAXPATHLEN], tobjname[MAXPATHLEN];
+	boolean_t already_logged;
 	int fobjerr, tobjerr;
 	int change;
 
@@ -257,14 +258,34 @@ write_inuse_diffs_one(FILE *fp, differ_info_t *di, uint64_t dobj)
 	 */
 	fobjerr = get_stats_for_obj(di, di->fromsnap, dobj, fobjname,
 	    MAXPATHLEN, &fsb);
-	if (fobjerr && di->zerr != ENOENT && di->zerr != ENOTSUP)
+	if (fobjerr && di->zerr != ENOENT && di->zerr != ENOTSUP &&
+	    di->zerr != EINVAL && di->zerr != ENOENT)
 		return (-1);
 
+	if (fobjerr && (di->zerr == EINVAL || di->zerr == ENOENT)) {
+		// previously, we printed out an error message on EINVAL and
+		// died immediately. Let's keep the error message but continue.
+		zfs_error_aux(di->zhp->zfs_hdl, strerror(di->zerr));
+		// the error code we pass here doesn't matter, because we filled
+		// in the message above
+		zfs_error(di->zhp->zfs_hdl, di->zerr, di->errbuf);
+		// let's not print an error for the same object twice - once for
+		// each snapshot
+		already_logged = B_TRUE;
+	}
+
 	tobjerr = get_stats_for_obj(di, di->tosnap, dobj, tobjname,
 	    MAXPATHLEN, &tsb);
-	if (tobjerr && di->zerr != ENOENT && di->zerr != ENOTSUP)
+	if (tobjerr && di->zerr != ENOENT && di->zerr != ENOTSUP &&
+	    di->zerr != EINVAL && di->zerr != ENOENT)
 		return (-1);
 
+	if (tobjerr && (di->zerr == EINVAL || di->zerr == ENOENT)) {
+		if (!already_logged) {
+			zfs_error_aux(di->zhp->zfs_hdl, strerror(di->zerr));
+			zfs_error(di->zhp->zfs_hdl, di->zerr, di->errbuf);
+		}
+	}
 	/*
 	 * Unallocated object sharing the same meta dnode block
 	 */