kboot: Probe all disks and partitions for a kernel

Guess where to boot from when bootdev= isn't on the command line or
other config. Search all the disks and partitions for one that looks
like it could be a boot partition (same as we do when probing
zpools). Return the first one we find.

Sponsored by:		Netflix
Reviewed by:		tsoome
Differential Revision:	https://reviews.freebsd.org/D38319

stand/kboot/hostdisk.c

@@ -488,6 +488,61 @@ hostdisk_parsedev(struct devdesc **idev, const char *devspec, const char **path)
 	return (0);
 }
 
+/* XXX refactor */
+static bool
+sanity_check_currdev(void)
+{
+	struct stat st;
+
+	return (stat(PATH_DEFAULTS_LOADER_CONF, &st) == 0 ||
+#ifdef PATH_BOOTABLE_TOKEN
+	    stat(PATH_BOOTABLE_TOKEN, &st) == 0 || /* non-standard layout */
+#endif
+	    stat(PATH_KERNEL, &st) == 0);
+}
+
+static const char *
+hostdisk_try_one(hdinfo_t *hd)
+{
+	char *fn;
+
+	if (asprintf(&fn, "%s:", hd->hd_dev) == -1)
+		return (NULL);
+	set_currdev(fn);
+	printf("Trying %s\n", fn);
+	if (sanity_check_currdev())
+		return (fn);
+	printf("Failed %s\n", fn);
+	free(fn);
+	return (NULL);
+}
+
+const char *
+hostdisk_gen_probe(void)
+{
+	hdinfo_t *hd, *md;
+	const char *rv = NULL;
+
+	STAILQ_FOREACH(hd, &hdinfo, hd_link) {
+		/* try whole disk */
+		if (hd->hd_flags & HDF_HAS_ZPOOL)
+			continue;
+		rv = hostdisk_try_one(hd);
+		if (rv != NULL)
+			return (rv);
+
+		/* try all partitions */
+		STAILQ_FOREACH(md, &hd->hd_children, hd_link) {
+			if (md->hd_flags & HDF_HAS_ZPOOL)
+				continue;
+			rv = hostdisk_try_one(md);
+			if (rv != NULL)
+				return (rv);
+		}
+	}
+	return (false);
+}
+
 #ifdef LOADER_ZFS_SUPPORT
 static bool
 hostdisk_zfs_check_one(hdinfo_t *hd)
@@ -524,19 +579,6 @@ hostdisk_zfs_probe(void)
 	}
 }
 
-/* XXX refactor */
-static bool
-sanity_check_currdev(void)
-{
-	struct stat st;
-
-	return (stat(PATH_DEFAULTS_LOADER_CONF, &st) == 0 ||
-#ifdef PATH_BOOTABLE_TOKEN
-	    stat(PATH_BOOTABLE_TOKEN, &st) == 0 || /* non-standard layout */
-#endif
-	    stat(PATH_KERNEL, &st) == 0);
-}
-
 /* This likely shoud move to libsa/zfs/zfs.c and be used by at least EFI booting */
 static bool
 probe_zfs_currdev(uint64_t pool_guid, uint64_t root_guid, bool setcurrdev)
@@ -599,5 +641,4 @@ hostdisk_zfs_find_default(void)
 	}
 	return (false);
 }
-
 #endif

stand/kboot/kboot.h

@@ -22,6 +22,7 @@ uint8_t kboot_get_kernel_machine_bits(void);
 
 /* hostdisk.c */
 extern const char *hostfs_root;
+const char *hostdisk_gen_probe(void);
 void hostdisk_zfs_probe(void);
 bool hostdisk_zfs_find_default(void);
 

stand/kboot/main.c

@@ -221,6 +221,8 @@ main(int argc, const char **argv)
 	devinit();
 
 	bootdev = getenv("bootdev");
+	if (bootdev == NULL)
+		bootdev = hostdisk_gen_probe();
 	if (bootdev == NULL)
 		bootdev="zfs:";
 	hostfs_root = getenv("hostfs_root");