efi_loader: add file/filesys support

fallback.efi (and probably other things) use UEFI's simple-file-system
protocol and file support to search for OS's to boot.

Signed-off-by: Rob Clark <robdclark@gmail.com>
[agraf: whitespace fixes, unsigned fixes]
Signed-off-by: Alexander Graf <agraf@suse.de>

7 files changed, 676 insertions, 0 deletions

diff --git a/include/efi.h b/include/efi.h
index 63cbdb6..a432c89 100644
--- a/include/efi.h
+++ b/include/efi.h
@@ -81,6 +81,8 @@ typedef struct {
 #define EFI_IP_ADDRESS_CONFLICT		(EFI_ERROR_MASK | 34)
 #define EFI_HTTP_ERROR			(EFI_ERROR_MASK | 35)
 
+#define EFI_WARN_DELETE_FAILURE	2
+
 typedef unsigned long efi_status_t;
 typedef u64 efi_physical_addr_t;
 typedef u64 efi_virtual_addr_t;
diff --git a/include/efi_api.h b/include/efi_api.h
index 0c36122..1aae963 100644
--- a/include/efi_api.h
+++ b/include/efi_api.h
@@ -666,4 +666,69 @@ struct efi_pxe {
 	struct efi_pxe_mode *mode;
 };
 
+#define EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_GUID \
+	EFI_GUID(0x964e5b22, 0x6459, 0x11d2, \
+		 0x8e, 0x39, 0x0, 0xa0, 0xc9, 0x69, 0x72, 0x3b)
+#define EFI_FILE_PROTOCOL_REVISION 0x00010000
+
+struct efi_file_handle {
+	u64 rev;
+	efi_status_t (EFIAPI *open)(struct efi_file_handle *file,
+			struct efi_file_handle **new_handle,
+			s16 *file_name, u64 open_mode, u64 attributes);
+	efi_status_t (EFIAPI *close)(struct efi_file_handle *file);
+	efi_status_t (EFIAPI *delete)(struct efi_file_handle *file);
+	efi_status_t (EFIAPI *read)(struct efi_file_handle *file,
+			u64 *buffer_size, void *buffer);
+	efi_status_t (EFIAPI *write)(struct efi_file_handle *file,
+			u64 *buffer_size, void *buffer);
+	efi_status_t (EFIAPI *getpos)(struct efi_file_handle *file,
+			u64 *pos);
+	efi_status_t (EFIAPI *setpos)(struct efi_file_handle *file,
+			u64 pos);
+	efi_status_t (EFIAPI *getinfo)(struct efi_file_handle *file,
+			efi_guid_t *info_type, u64 *buffer_size, void *buffer);
+	efi_status_t (EFIAPI *setinfo)(struct efi_file_handle *file,
+			efi_guid_t *info_type, u64 buffer_size, void *buffer);
+	efi_status_t (EFIAPI *flush)(struct efi_file_handle *file);
+};
+
+#define EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_GUID \
+	EFI_GUID(0x964e5b22, 0x6459, 0x11d2, \
+		 0x8e, 0x39, 0x0, 0xa0, 0xc9, 0x69, 0x72, 0x3b)
+#define EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_REVISION 0x00010000
+
+struct efi_simple_file_system_protocol {
+	u64 rev;
+	efi_status_t (EFIAPI *open_volume)(struct efi_simple_file_system_protocol *this,
+			struct efi_file_handle **root);
+};
+
+#define EFI_FILE_INFO_GUID \
+	EFI_GUID(0x9576e92, 0x6d3f, 0x11d2, \
+		 0x8e, 0x39, 0x0, 0xa0, 0xc9, 0x69, 0x72, 0x3b)
+
+#define EFI_FILE_MODE_READ	0x0000000000000001
+#define EFI_FILE_MODE_WRITE	0x0000000000000002
+#define EFI_FILE_MODE_CREATE	0x8000000000000000
+
+#define EFI_FILE_READ_ONLY	0x0000000000000001
+#define EFI_FILE_HIDDEN		0x0000000000000002
+#define EFI_FILE_SYSTEM		0x0000000000000004
+#define EFI_FILE_RESERVED	0x0000000000000008
+#define EFI_FILE_DIRECTORY	0x0000000000000010
+#define EFI_FILE_ARCHIVE	0x0000000000000020
+#define EFI_FILE_VALID_ATTR	0x0000000000000037
+
+struct efi_file_info {
+	u64 size;
+	u64 file_size;
+	u64 physical_size;
+	struct efi_time create_time;
+	struct efi_time last_access_time;
+	struct efi_time modification_time;
+	u64 attribute;
+	s16 file_name[0];
+};
+
 #endif
diff --git a/include/efi_loader.h b/include/efi_loader.h
index 8752bcf..9cb0644 100644
--- a/include/efi_loader.h
+++ b/include/efi_loader.h
@@ -86,6 +86,8 @@ extern const efi_guid_t efi_guid_console_control;
 extern const efi_guid_t efi_guid_device_path;
 extern const efi_guid_t efi_guid_loaded_image;
 extern const efi_guid_t efi_guid_device_path_to_text_protocol;
+extern const efi_guid_t efi_simple_file_system_protocol_guid;
+extern const efi_guid_t efi_file_info_guid;
 
 extern unsigned int __efi_runtime_start, __efi_runtime_stop;
 extern unsigned int __efi_runtime_rel_start, __efi_runtime_rel_stop;
@@ -163,6 +165,9 @@ int efi_net_register(void);
 /* Called by bootefi to make SMBIOS tables available */
 void efi_smbios_register(void);
 
+struct efi_simple_file_system_protocol *
+efi_fs_from_path(struct efi_device_path *fp);
+
 /* Called by networking code to memorize the dhcp ack package */
 void efi_net_set_dhcp_ack(void *pkt, int len);
 
@@ -191,6 +196,14 @@ efi_status_t efi_set_timer(struct efi_event *event, enum efi_timer_delay type,
 /* Call this to signal an event */
 void efi_signal_event(struct efi_event *event);
 
+/* open file system: */
+struct efi_simple_file_system_protocol *efi_simple_file_system(
+		struct blk_desc *desc, int part, struct efi_device_path *dp);
+
+/* open file from device-path: */
+struct efi_file_handle *efi_file_from_path(struct efi_device_path *fp);
+
+
 /* Generic EFI memory allocator, call this to get memory */
 void *efi_alloc(uint64_t len, int memory_type);
 /* More specific EFI memory allocator, called by EFI payloads */
diff --git a/lib/efi_loader/Makefile b/lib/efi_loader/Makefile
index e68b0dd..00919ce 100644
--- a/lib/efi_loader/Makefile
+++ b/lib/efi_loader/Makefile
@@ -17,6 +17,7 @@ endif
 obj-$(CONFIG_CMD_BOOTEFI_HELLO) += helloworld_efi.o
 obj-y += efi_image_loader.o efi_boottime.o efi_runtime.o efi_console.o
 obj-y += efi_memory.o efi_device_path_to_text.o efi_device_path.o
+obj-y += efi_file.o
 obj-$(CONFIG_LCD) += efi_gop.o
 obj-$(CONFIG_DM_VIDEO) += efi_gop.o
 obj-$(CONFIG_PARTITIONS) += efi_disk.o
diff --git a/lib/efi_loader/efi_disk.c b/lib/efi_loader/efi_disk.c
index c815711..eb9ce77 100644
--- a/lib/efi_loader/efi_disk.c
+++ b/lib/efi_loader/efi_disk.c
@@ -31,6 +31,8 @@ struct efi_disk_obj {
 	struct efi_device_path *dp;
 	/* partition # */
 	unsigned int part;
+	/* handle to filesys proto (for partition objects) */
+	struct efi_simple_file_system_protocol *volume;
 	/* Offset into disk for simple partitions */
 	lbaint_t offset;
 	/* Internal block device */
@@ -172,6 +174,28 @@ static const struct efi_block_io block_io_disk_template = {
 	.flush_blocks = &efi_disk_flush_blocks,
 };
 
+/*
+ * Find filesystem from a device-path.  The passed in path 'p' probably
+ * contains one or more /File(name) nodes, so the comparison stops at
+ * the first /File() node, and returns the pointer to that via 'rp'.
+ * This is mostly intended to be a helper to map a device-path to an
+ * efi_file_handle object.
+ */
+struct efi_simple_file_system_protocol *
+efi_fs_from_path(struct efi_device_path *fp)
+{
+	struct efi_object *efiobj;
+	struct efi_disk_obj *diskobj;
+
+	efiobj = efi_dp_find_obj(fp, NULL);
+	if (!efiobj)
+		return NULL;
+
+	diskobj = container_of(efiobj, struct efi_disk_obj, parent);
+
+	return diskobj->volume;
+}
+
 static void efi_disk_add_dev(const char *name,
 			     const char *if_typename,
 			     struct blk_desc *desc,
@@ -194,6 +218,14 @@ static void efi_disk_add_dev(const char *name,
 	diskobj->parent.protocols[0].protocol_interface = &diskobj->ops;
 	diskobj->parent.protocols[1].guid = &efi_guid_device_path;
 	diskobj->parent.protocols[1].protocol_interface = diskobj->dp;
+	if (part >= 1) {
+		diskobj->volume = efi_simple_file_system(desc, part,
+							 diskobj->dp);
+		diskobj->parent.protocols[2].guid =
+			&efi_simple_file_system_protocol_guid;
+		diskobj->parent.protocols[2].protocol_interface =
+			diskobj->volume;
+	}
 	diskobj->parent.handle = diskobj;
 	diskobj->ops = block_io_disk_template;
 	diskobj->ifname = if_typename;
diff --git a/lib/efi_loader/efi_file.c b/lib/efi_loader/efi_file.c
new file mode 100644
index 0000000..52a4e74
--- /dev/null
+++ b/lib/efi_loader/efi_file.c
@@ -0,0 +1,560 @@
+/*
+ *  EFI utils
+ *
+ *  Copyright (c) 2017 Rob Clark
+ *
+ *  SPDX-License-Identifier:     GPL-2.0+
+ */
+
+#include <common.h>
+#include <charset.h>
+#include <efi_loader.h>
+#include <malloc.h>
+#include <fs.h>
+
+struct file_system {
+	struct efi_simple_file_system_protocol base;
+	struct efi_device_path *dp;
+	struct blk_desc *desc;
+	int part;
+};
+#define to_fs(x) container_of(x, struct file_system, base)
+
+struct file_handle {
+	struct efi_file_handle base;
+	struct file_system *fs;
+	loff_t offset;       /* current file position/cursor */
+	int isdir;
+
+	/* for reading a directory: */
+	struct fs_dir_stream *dirs;
+	struct fs_dirent *dent;
+
+	char path[0];
+};
+#define to_fh(x) container_of(x, struct file_handle, base)
+
+static const struct efi_file_handle efi_file_handle_protocol;
+
+static char *basename(struct file_handle *fh)
+{
+	char *s = strrchr(fh->path, '/');
+	if (s)
+		return s + 1;
+	return fh->path;
+}
+
+static int set_blk_dev(struct file_handle *fh)
+{
+	return fs_set_blk_dev_with_part(fh->fs->desc, fh->fs->part);
+}
+
+static int is_dir(struct file_handle *fh)
+{
+	struct fs_dir_stream *dirs;
+
+	set_blk_dev(fh);
+	dirs = fs_opendir(fh->path);
+	if (!dirs)
+		return 0;
+
+	fs_closedir(dirs);
+
+	return 1;
+}
+
+/*
+ * Normalize a path which may include either back or fwd slashes,
+ * double slashes, . or .. entries in the path, etc.
+ */
+static int sanitize_path(char *path)
+{
+	char *p;
+
+	/* backslash to slash: */
+	p = path;
+	while ((p = strchr(p, '\\')))
+		*p++ = '/';
+
+	/* handle double-slashes: */
+	p = path;
+	while ((p = strstr(p, "//"))) {
+		char *src = p + 1;
+		memmove(p, src, strlen(src) + 1);
+	}
+
+	/* handle extra /.'s */
+	p = path;
+	while ((p = strstr(p, "/."))) {
+		/*
+		 * You'd be tempted to do this *after* handling ".."s
+		 * below to avoid having to check if "/." is start of
+		 * a "/..", but that won't have the correct results..
+		 * for example, "/foo/./../bar" would get resolved to
+		 * "/foo/bar" if you did these two passes in the other
+		 * order
+		 */
+		if (p[2] == '.') {
+			p += 2;
+			continue;
+		}
+		char *src = p + 2;
+		memmove(p, src, strlen(src) + 1);
+	}
+
+	/* handle extra /..'s: */
+	p = path;
+	while ((p = strstr(p, "/.."))) {
+		char *src = p + 3;
+
+		p--;
+
+		/* find beginning of previous path entry: */
+		while (true) {
+			if (p < path)
+				return -1;
+			if (*p == '/')
+				break;
+			p--;
+		}
+
+		memmove(p, src, strlen(src) + 1);
+	}
+
+	return 0;
+}
+
+/* NOTE: despite what you would expect, 'file_name' is actually a path.
+ * With windoze style backlashes, ofc.
+ */
+static struct efi_file_handle *file_open(struct file_system *fs,
+		struct file_handle *parent, s16 *file_name, u64 mode)
+{
+	struct file_handle *fh;
+	char f0[MAX_UTF8_PER_UTF16] = {0};
+	int plen = 0;
+	int flen = 0;
+
+	if (file_name) {
+		utf16_to_utf8((u8 *)f0, (u16 *)file_name, 1);
+		flen = utf16_strlen((u16 *)file_name);
+	}
+
+	/* we could have a parent, but also an absolute path: */
+	if (f0[0] == '\\') {
+		plen = 0;
+	} else if (parent) {
+		plen = strlen(parent->path) + 1;
+	}
+
+	/* +2 is for null and '/' */
+	fh = calloc(1, sizeof(*fh) + plen + (flen * MAX_UTF8_PER_UTF16) + 2);
+
+	fh->base = efi_file_handle_protocol;
+	fh->fs = fs;
+
+	if (parent) {
+		char *p = fh->path;
+
+		if (plen > 0) {
+			strcpy(p, parent->path);
+			p += plen - 1;
+			*p++ = '/';
+		}
+
+		utf16_to_utf8((u8 *)p, (u16 *)file_name, flen);
+
+		if (sanitize_path(fh->path))
+			goto error;
+
+		/* check if file exists: */
+		if (set_blk_dev(fh))
+			goto error;
+
+		if (!((mode & EFI_FILE_MODE_CREATE) || fs_exists(fh->path)))
+			goto error;
+
+		/* figure out if file is a directory: */
+		fh->isdir = is_dir(fh);
+	} else {
+		fh->isdir = 1;
+		strcpy(fh->path, "");
+	}
+
+	return &fh->base;
+
+error:
+	free(fh);
+	return NULL;
+}
+
+static efi_status_t EFIAPI efi_file_open(struct efi_file_handle *file,
+		struct efi_file_handle **new_handle,
+		s16 *file_name, u64 open_mode, u64 attributes)
+{
+	struct file_handle *fh = to_fh(file);
+
+	EFI_ENTRY("%p, %p, \"%ls\", %llx, %llu", file, new_handle, file_name,
+		  open_mode, attributes);
+
+	*new_handle = file_open(fh->fs, fh, file_name, open_mode);
+	if (!*new_handle)
+		return EFI_EXIT(EFI_NOT_FOUND);
+
+	return EFI_EXIT(EFI_SUCCESS);
+}
+
+static efi_status_t file_close(struct file_handle *fh)
+{
+	fs_closedir(fh->dirs);
+	free(fh);
+	return EFI_SUCCESS;
+}
+
+static efi_status_t EFIAPI efi_file_close(struct efi_file_handle *file)
+{
+	struct file_handle *fh = to_fh(file);
+	EFI_ENTRY("%p", file);
+	return EFI_EXIT(file_close(fh));
+}
+
+static efi_status_t EFIAPI efi_file_delete(struct efi_file_handle *file)
+{
+	struct file_handle *fh = to_fh(file);
+	EFI_ENTRY("%p", file);
+	file_close(fh);
+	return EFI_EXIT(EFI_WARN_DELETE_FAILURE);
+}
+
+static efi_status_t file_read(struct file_handle *fh, u64 *buffer_size,
+		void *buffer)
+{
+	loff_t actread;
+
+	if (fs_read(fh->path, (ulong)buffer, fh->offset,
+		    *buffer_size, &actread))
+		return EFI_DEVICE_ERROR;
+
+	*buffer_size = actread;
+	fh->offset += actread;
+
+	return EFI_SUCCESS;
+}
+
+static efi_status_t dir_read(struct file_handle *fh, u64 *buffer_size,
+		void *buffer)
+{
+	struct efi_file_info *info = buffer;
+	struct fs_dirent *dent;
+	unsigned int required_size;
+
+	if (!fh->dirs) {
+		assert(fh->offset == 0);
+		fh->dirs = fs_opendir(fh->path);
+		if (!fh->dirs)
+			return EFI_DEVICE_ERROR;
+	}
+
+	/*
+	 * So this is a bit awkward.  Since fs layer is stateful and we
+	 * can't rewind an entry, in the EFI_BUFFER_TOO_SMALL case below
+	 * we might have to return without consuming the dent.. so we
+	 * have to stash it for next call.
+	 */
+	if (fh->dent) {
+		dent = fh->dent;
+		fh->dent = NULL;
+	} else {
+		dent = fs_readdir(fh->dirs);
+	}
+
+
+	if (!dent) {
+		/* no more files in directory: */
+		/* workaround shim.efi bug/quirk.. as find_boot_csv()
+		 * loops through directory contents, it initially calls
+		 * read w/ zero length buffer to find out how much mem
+		 * to allocate for the EFI_FILE_INFO, then allocates,
+		 * and then calls a 2nd time.  If we return size of
+		 * zero the first time, it happily passes that to
+		 * AllocateZeroPool(), and when that returns NULL it
+		 * thinks it is EFI_OUT_OF_RESOURCES.  So on first
+		 * call return a non-zero size:
+		 */
+		if (*buffer_size == 0)
+			*buffer_size = sizeof(*info);
+		else
+			*buffer_size = 0;
+		return EFI_SUCCESS;
+	}
+
+	/* check buffer size: */
+	required_size = sizeof(*info) + 2 * (strlen(dent->name) + 1);
+	if (*buffer_size < required_size) {
+		*buffer_size = required_size;
+		fh->dent = dent;
+		return EFI_BUFFER_TOO_SMALL;
+	}
+
+	*buffer_size = required_size;
+	memset(info, 0, required_size);
+
+	info->size = required_size;
+	info->file_size = dent->size;
+	info->physical_size = dent->size;
+
+	if (dent->type == FS_DT_DIR)
+		info->attribute |= EFI_FILE_DIRECTORY;
+
+	ascii2unicode((u16 *)info->file_name, dent->name);
+
+	fh->offset++;
+
+	return EFI_SUCCESS;
+}
+
+static efi_status_t EFIAPI efi_file_read(struct efi_file_handle *file,
+		u64 *buffer_size, void *buffer)
+{
+	struct file_handle *fh = to_fh(file);
+	efi_status_t ret = EFI_SUCCESS;
+
+	EFI_ENTRY("%p, %p, %p", file, buffer_size, buffer);
+
+	if (set_blk_dev(fh)) {
+		ret = EFI_DEVICE_ERROR;
+		goto error;
+	}
+
+	if (fh->isdir)
+		ret = dir_read(fh, buffer_size, buffer);
+	else
+		ret = file_read(fh, buffer_size, buffer);
+
+error:
+	return EFI_EXIT(ret);
+}
+
+static efi_status_t EFIAPI efi_file_write(struct efi_file_handle *file,
+		u64 *buffer_size, void *buffer)
+{
+	struct file_handle *fh = to_fh(file);
+	efi_status_t ret = EFI_SUCCESS;
+	loff_t actwrite;
+
+	EFI_ENTRY("%p, %p, %p", file, buffer_size, buffer);
+
+	if (set_blk_dev(fh)) {
+		ret = EFI_DEVICE_ERROR;
+		goto error;
+	}
+
+	if (fs_write(fh->path, (ulong)buffer, fh->offset, *buffer_size,
+		     &actwrite)) {
+		ret = EFI_DEVICE_ERROR;
+		goto error;
+	}
+
+	*buffer_size = actwrite;
+	fh->offset += actwrite;
+
+error:
+	return EFI_EXIT(ret);
+}
+
+static efi_status_t EFIAPI efi_file_getpos(struct efi_file_handle *file,
+		u64 *pos)
+{
+	struct file_handle *fh = to_fh(file);
+	EFI_ENTRY("%p, %p", file, pos);
+	*pos = fh->offset;
+	return EFI_EXIT(EFI_SUCCESS);
+}
+
+static efi_status_t EFIAPI efi_file_setpos(struct efi_file_handle *file,
+		u64 pos)
+{
+	struct file_handle *fh = to_fh(file);
+	efi_status_t ret = EFI_SUCCESS;
+
+	EFI_ENTRY("%p, %llu", file, pos);
+
+	if (fh->isdir) {
+		if (pos != 0) {
+			ret = EFI_UNSUPPORTED;
+			goto error;
+		}
+		fs_closedir(fh->dirs);
+		fh->dirs = NULL;
+	}
+
+	if (pos == ~0ULL) {
+		loff_t file_size;
+
+		if (set_blk_dev(fh)) {
+			ret = EFI_DEVICE_ERROR;
+			goto error;
+		}
+
+		if (fs_size(fh->path, &file_size)) {
+			ret = EFI_DEVICE_ERROR;
+			goto error;
+		}
+
+		pos = file_size;
+	}
+
+	fh->offset = pos;
+
+error:
+	return EFI_EXIT(ret);
+}
+
+static efi_status_t EFIAPI efi_file_getinfo(struct efi_file_handle *file,
+		efi_guid_t *info_type, u64 *buffer_size, void *buffer)
+{
+	struct file_handle *fh = to_fh(file);
+	efi_status_t ret = EFI_SUCCESS;
+
+	EFI_ENTRY("%p, %p, %p, %p", file, info_type, buffer_size, buffer);
+
+	if (!guidcmp(info_type, &efi_file_info_guid)) {
+		struct efi_file_info *info = buffer;
+		char *filename = basename(fh);
+		unsigned int required_size;
+		loff_t file_size;
+
+		/* check buffer size: */
+		required_size = sizeof(*info) + 2 * (strlen(filename) + 1);
+		if (*buffer_size < required_size) {
+			*buffer_size = required_size;
+			ret = EFI_BUFFER_TOO_SMALL;
+			goto error;
+		}
+
+		if (set_blk_dev(fh)) {
+			ret = EFI_DEVICE_ERROR;
+			goto error;
+		}
+
+		if (fs_size(fh->path, &file_size)) {
+			ret = EFI_DEVICE_ERROR;
+			goto error;
+		}
+
+		memset(info, 0, required_size);
+
+		info->size = required_size;
+		info->file_size = file_size;
+		info->physical_size = file_size;
+
+		if (fh->isdir)
+			info->attribute |= EFI_FILE_DIRECTORY;
+
+		ascii2unicode((u16 *)info->file_name, filename);
+	} else {
+		ret = EFI_UNSUPPORTED;
+	}
+
+error:
+	return EFI_EXIT(ret);
+}
+
+static efi_status_t EFIAPI efi_file_setinfo(struct efi_file_handle *file,
+		efi_guid_t *info_type, u64 buffer_size, void *buffer)
+{
+	EFI_ENTRY("%p, %p, %llu, %p", file, info_type, buffer_size, buffer);
+	return EFI_EXIT(EFI_UNSUPPORTED);
+}
+
+static efi_status_t EFIAPI efi_file_flush(struct efi_file_handle *file)
+{
+	EFI_ENTRY("%p", file);
+	return EFI_EXIT(EFI_SUCCESS);
+}
+
+static const struct efi_file_handle efi_file_handle_protocol = {
+	.rev = EFI_FILE_PROTOCOL_REVISION,
+	.open = efi_file_open,
+	.close = efi_file_close,
+	.delete = efi_file_delete,
+	.read = efi_file_read,
+	.write = efi_file_write,
+	.getpos = efi_file_getpos,
+	.setpos = efi_file_setpos,
+	.getinfo = efi_file_getinfo,
+	.setinfo = efi_file_setinfo,
+	.flush = efi_file_flush,
+};
+
+struct efi_file_handle *efi_file_from_path(struct efi_device_path *fp)
+{
+	struct efi_simple_file_system_protocol *v;
+	struct efi_file_handle *f;
+	efi_status_t ret;
+
+	v = efi_fs_from_path(fp);
+	if (!v)
+		return NULL;
+
+	EFI_CALL(ret = v->open_volume(v, &f));
+	if (ret != EFI_SUCCESS)
+		return NULL;
+
+	/* skip over device-path nodes before the file path: */
+	while (fp && !EFI_DP_TYPE(fp, MEDIA_DEVICE, FILE_PATH))
+		fp = efi_dp_next(fp);
+
+	while (fp) {
+		struct efi_device_path_file_path *fdp =
+			container_of(fp, struct efi_device_path_file_path, dp);
+		struct efi_file_handle *f2;
+
+		if (!EFI_DP_TYPE(fp, MEDIA_DEVICE, FILE_PATH)) {
+			printf("bad file path!\n");
+			f->close(f);
+			return NULL;
+		}
+
+		EFI_CALL(ret = f->open(f, &f2, (s16 *)fdp->str,
+				       EFI_FILE_MODE_READ, 0));
+		if (ret != EFI_SUCCESS)
+			return NULL;
+
+		fp = efi_dp_next(fp);
+
+		EFI_CALL(f->close(f));
+		f = f2;
+	}
+
+	return f;
+}
+
+static efi_status_t EFIAPI
+efi_open_volume(struct efi_simple_file_system_protocol *this,
+		struct efi_file_handle **root)
+{
+	struct file_system *fs = to_fs(this);
+
+	EFI_ENTRY("%p, %p", this, root);
+
+	*root = file_open(fs, NULL, NULL, 0);
+
+	return EFI_EXIT(EFI_SUCCESS);
+}
+
+struct efi_simple_file_system_protocol *
+efi_simple_file_system(struct blk_desc *desc, int part,
+		       struct efi_device_path *dp)
+{
+	struct file_system *fs;
+
+	fs = calloc(1, sizeof(*fs));
+	fs->base.rev = EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_REVISION;
+	fs->base.open_volume = efi_open_volume;
+	fs->desc = desc;
+	fs->part = part;
+	fs->dp = dp;
+
+	return &fs->base;
+}
diff --git a/lib/efi_loader/efi_image_loader.c b/lib/efi_loader/efi_image_loader.c
index f961407..469acae 100644
--- a/lib/efi_loader/efi_image_loader.c
+++ b/lib/efi_loader/efi_image_loader.c
@@ -17,6 +17,9 @@ DECLARE_GLOBAL_DATA_PTR;
 
 const efi_guid_t efi_guid_device_path = DEVICE_PATH_GUID;
 const efi_guid_t efi_guid_loaded_image = LOADED_IMAGE_GUID;
+const efi_guid_t efi_simple_file_system_protocol_guid =
+		EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_GUID;
+const efi_guid_t efi_file_info_guid = EFI_FILE_INFO_GUID;
 
 static efi_status_t efi_loader_relocate(const IMAGE_BASE_RELOCATION *rel,
 			unsigned long rel_size, void *efi_reloc)