+ *p = x;
+ return 0;
+}
+
+static size_t utf16_size(const uint16_t *s) {
+ size_t l = 0;
+
+ while (s[l] > 0)
+ l++;
+
+ return (l+1) * sizeof(uint16_t);
+}
+
+static void efi_guid_to_id128(const void *guid, sd_id128_t *id128) {
+ struct uuid {
+ uint32_t u1;
+ uint16_t u2;
+ uint16_t u3;
+ uint8_t u4[8];
+ } _packed_;
+ const struct uuid *uuid = guid;
+
+ id128->bytes[0] = (uuid->u1 >> 24) & 0xff;
+ id128->bytes[1] = (uuid->u1 >> 16) & 0xff;
+ id128->bytes[2] = (uuid->u1 >> 8) & 0xff;
+ id128->bytes[3] = (uuid->u1) & 0xff;
+ id128->bytes[4] = (uuid->u2 >> 8) & 0xff;
+ id128->bytes[5] = (uuid->u2) & 0xff;
+ id128->bytes[6] = (uuid->u3 >> 8) & 0xff;
+ id128->bytes[7] = (uuid->u3) & 0xff;
+ memcpy(&id128->bytes[8], uuid->u4, sizeof(uuid->u4));
+}
+
+int efi_get_boot_option(
+ uint16_t id,
+ char **title,
+ sd_id128_t *part_uuid,
+ char **path) {
+
+ struct boot_option {
+ uint32_t attr;
+ uint16_t path_len;
+ uint16_t title[];
+ } _packed_;
+
+ struct drive_path {
+ uint32_t part_nr;
+ uint64_t part_start;
+ uint64_t part_size;
+ char signature[16];
+ uint8_t mbr_type;
+ uint8_t signature_type;
+ } _packed_;
+
+ struct device_path {
+ uint8_t type;
+ uint8_t sub_type;
+ uint16_t length;
+ union {
+ uint16_t path[0];
+ struct drive_path drive;
+ };
+ } _packed_;
+
+ char boot_id[9];
+ _cleanup_free_ uint8_t *buf = NULL;
+ size_t l;
+ struct boot_option *header;
+ size_t title_size;
+ char *s = NULL;
+ char *p = NULL;
+ sd_id128_t p_uuid = SD_ID128_NULL;
+ int err;
+
+ snprintf(boot_id, sizeof(boot_id), "Boot%04X", id);
+ err = efi_get_variable(EFI_VENDOR_GLOBAL, boot_id, NULL, (void **)&buf, &l);
+ if (err < 0)
+ return err;
+ if (l < sizeof(struct boot_option))
+ return -ENOENT;
+
+ header = (struct boot_option *)buf;
+ title_size = utf16_size(header->title);
+ if (title_size > l - offsetof(struct boot_option, title))
+ return -EINVAL;
+
+ if (title) {
+ s = utf16_to_utf8(header->title, title_size);
+ if (!s) {
+ err = -ENOMEM;
+ goto err;
+ }
+ }
+
+ if (header->path_len > 0) {
+ uint8_t *dbuf;
+ size_t dnext;
+
+ dbuf = buf + offsetof(struct boot_option, title) + title_size;
+ dnext = 0;
+ while (dnext < header->path_len) {
+ struct device_path *dpath;
+
+ dpath = (struct device_path *)(dbuf + dnext);
+ if (dpath->length < 4)
+ break;
+
+ /* Type 0x7F – End of Hardware Device Path, Sub-Type 0xFF – End Entire Device Path */
+ if (dpath->type == 0x7f && dpath->sub_type == 0xff)
+ break;
+
+ dnext += dpath->length;
+
+ /* Type 0x04 – Media Device Path */
+ if (dpath->type != 0x04)
+ continue;
+
+ /* Sub-Type 1 – Hard Drive */
+ if (dpath->sub_type == 0x01) {
+ /* 0x02 – GUID Partition Table */
+ if (dpath->drive.mbr_type != 0x02)
+ continue;
+
+ /* 0x02 – GUID signature */
+ if (dpath->drive.signature_type != 0x02)
+ continue;
+
+ if (part_uuid)
+ efi_guid_to_id128(dpath->drive.signature, &p_uuid);
+ continue;
+ }
+
+ /* Sub-Type 4 – File Path */
+ if (dpath->sub_type == 0x04 && !p && path) {
+ p = utf16_to_utf8(dpath->path, dpath->length-4);
+ continue;
+ }
+ }
+ }
+
+ if (title)
+ *title = s;
+ if (part_uuid)
+ *part_uuid = p_uuid;
+ if (path)
+ *path = p;
+
+ return 0;
+err:
+ free(s);
+ free(p);
+ return err;
+}