fusefs: attempt to support servers as old as protocol 7.4

Previously we allowed servers as old as 7.1 to connect (there never was a
7.0).  However, we wrongly assumed a few things about protocols older than
7.8.  This commit attempts to support servers as old as 7.4 but no older.  I
added no new tests because I'm not sure there actually _are_ any servers
this old in the wild.

Sponsored by:	The FreeBSD Foundation

1 files changed, 6 insertions, 4 deletions

diff --git a/sys/fs/fuse/fuse_vfsops.c b/sys/fs/fuse/fuse_vfsops.c
index 64d7ccc7600c..f64b69164e5f 100644
--- a/sys/fs/fuse/fuse_vfsops.c
+++ b/sys/fs/fuse/fuse_vfsops.c
@@ -493,11 +493,13 @@ fuse_vfsop_unmount(struct mount *mp, int mntflags)
 	if (fdata_get_dead(data)) {
 		goto alreadydead;
 	}
-	fdisp_init(&fdi, 0);
-	fdisp_make(&fdi, FUSE_DESTROY, mp, 0, td, NULL);
+	if (fsess_isimpl(mp, FUSE_DESTROY)) {
+		fdisp_init(&fdi, 0);
+		fdisp_make(&fdi, FUSE_DESTROY, mp, 0, td, NULL);
 
-	err = fdisp_wait_answ(&fdi);
-	fdisp_destroy(&fdi);
+		(void)fdisp_wait_answ(&fdi);
+		fdisp_destroy(&fdi);
+	}
 
 	fdata_set_dead(data);