Index: usr.sbin/bhyve/block_if.c
===================================================================
--- usr.sbin/bhyve/block_if.c   (revision 286768)
+++ usr.sbin/bhyve/block_if.c   (working copy)
@@ -392,6 +392,7 @@
 {
        char tname[MAXCOMLEN + 1];
        char name[MAXPATHLEN];
+       char errstr[MAXPATHLEN+64];     /* allow error text to be 64 chars long */
        char *nopt, *xopts, *cp;
        struct blockif_ctxt *bc;
        struct stat sbuf;
@@ -447,12 +448,14 @@
        }

        if (fd < 0) {
-               perror("Could not open backing file");
+               snprintf(errstr, sizeof(errstr), "Could not open backing file: %s", nopt);
+               perror(errstr);
                goto err;
        }

         if (fstat(fd, &sbuf) < 0) {
-                perror("Could not stat backing file");
+               snprintf(errstr, sizeof(errstr), "Could not stat backing file: %s", nopt);
+               perror(errstr);
                goto err;
         }

Index: usr.sbin/bhyve/pci_virtio_block.c
===================================================================
--- usr.sbin/bhyve/pci_virtio_block.c   (revision 286768)
+++ usr.sbin/bhyve/pci_virtio_block.c   (working copy)
@@ -296,6 +296,7 @@
        struct pci_vtblk_softc *sc;
        off_t size;
        int i, sectsz, sts, sto;
+       char errstr[MAXPATHLEN+64];     /* allow error text to be 64 chars long */

        if (opts == NULL) {
                printf("virtio-block: backing device required\n");
@@ -308,7 +309,8 @@
        snprintf(bident, sizeof(bident), "%d:%d", pi->pi_slot, pi->pi_func);
        bctxt = blockif_open(opts, bident);
        if (bctxt == NULL) {
-               perror("Could not open backing file");
+               snprintf(errstr, sizeof(errstr), "Could not open backing file: %s", opts);
+               perror(errstr);
                return (1);
        }