loader.efi: efiblk_memdisk_preload passes the VirtualDisks to FreeBSD

Set hint.md.%d.physaddr and hint.md.%d.len for each of the VirtualDisks.
The memory for these remains after we exit boot services so FreeBSD can
use them. This leverages the BIOS work we did for memdisks. In
hindsight, I should have passed this in via metadata, but it's been in a
release.

Sponsored by:		Netflix
Differential Revision:	https://reviews.freebsd.org/D57806

stand/efi/include/efilib.h

@@ -68,6 +68,7 @@ pdinfo_list_t *efiblk_get_pdinfo_list(struct devsw *dev);
 pdinfo_t *efiblk_get_pdinfo(struct devdesc *dev);
 pdinfo_t *efiblk_get_pdinfo_by_handle(EFI_HANDLE h);
 pdinfo_t *efiblk_get_pdinfo_by_device_path(EFI_DEVICE_PATH *path);
+void efiblk_memdisk_preload(void);
 
 /* libefi.c */
 void *efi_get_table(EFI_GUID *tbl);

stand/efi/libefi/efipart.c

@@ -1250,3 +1250,47 @@ error:
 		free(blkbuf);
 	return (rc);
 }
+
+/*
+ * Predicate: is this a VirtualDisk as far as UEFI is concerned?
+ */
+static bool
+testmd(pdinfo_t *hd, pdinfo_t *data __unused)
+{
+	EFI_DEVICE_PATH *node;
+
+	node = efi_devpath_last_node(hd->pd_devpath);
+	if (node == NULL)
+		return (false);
+	if (DevicePathType(node) == MEDIA_DEVICE_PATH &&
+	    DevicePathSubType(node) == MEDIA_RAM_DISK_DP)
+		return (true);
+
+	return (false);
+}
+
+/*
+ * Passes all the VirtualDisk instances to FreeBSD as a preloaded memory disk.
+ */
+void
+efiblk_memdisk_preload(void)
+{
+	MEDIA_RAM_DISK_DEVICE_PATH *ram;
+	uint64_t start, end;
+	pdinfo_t *md;
+	char key[32], value[32];
+	int i;
+
+	while ((md = efipart_get_pd(&pdinfo, testmd, NULL)) != NULL) {
+		ram = (MEDIA_RAM_DISK_DEVICE_PATH *)efi_devpath_last_node(md->pd_devpath);
+		i = ram->Instance;
+		start = ((uint64_t)ram->StartingAddr[1] << 32) | ram->StartingAddr[0];
+		end = ((uint64_t)ram->EndingAddr[1] << 32) | ram->EndingAddr[0];
+		snprintf(key, sizeof(key), "hint.md.%d.physaddr", i);
+		snprintf(value, sizeof(value), "0x%016x", start);
+		setenv(key, value, 1);
+		snprintf(key, sizeof(key), "hint.md.%d.len", i);
+		snprintf(value, sizeof(value), "0x%016x", end - start);
+		setenv(key, value, 1);
+	}
+}