+static bool
+is_resource_valid_for_external_backing(const struct wim_resource_descriptor *rdesc,
+ struct win32_apply_ctx *ctx)
+{
+ /* Must be the original WIM file format. This check excludes pipable
+ * resources and solid resources. It also excludes other resources
+ * contained in such files even if they would be otherwise compatible.
+ */
+ if (rdesc->wim->hdr.magic != WIM_MAGIC ||
+ rdesc->wim->hdr.wim_version != WIM_VERSION_DEFAULT)
+ {
+ ctx->wimboot.have_wrong_version_wims = true;
+ return false;
+ }
+
+ /*
+ * Whitelist of compression types and chunk sizes supported by
+ * Microsoft's WOF driver.
+ *
+ * Notes:
+ * - Uncompressed WIMs result in BSOD. However, this only applies to
+ * the WIM file itself, not to uncompressed resources in a WIM file
+ * that is otherwise compressed.
+ * - XPRESS 64K sometimes appears to work, but sometimes it causes
+ * reads to fail with STATUS_UNSUCCESSFUL.
+ */
+ switch (rdesc->compression_type) {
+ case WIMLIB_COMPRESSION_TYPE_NONE:
+ if (rdesc->wim->compression_type == WIMLIB_COMPRESSION_TYPE_NONE) {
+ ctx->wimboot.have_uncompressed_wims = true;
+ return false;
+ }
+ break;
+ case WIMLIB_COMPRESSION_TYPE_XPRESS:
+ switch (rdesc->chunk_size) {
+ case 4096:
+ case 8192:
+ case 16384:
+ case 32768:
+ break;
+ default:
+ ctx->wimboot.have_unsupported_compressed_resources = true;
+ return false;
+ }
+ break;
+ case WIMLIB_COMPRESSION_TYPE_LZX:
+ switch (rdesc->chunk_size) {
+ case 32768:
+ break;
+ default:
+ ctx->wimboot.have_unsupported_compressed_resources = true;
+ return false;
+ }
+ break;
+ default:
+ ctx->wimboot.have_unsupported_compressed_resources = true;
+ return false;
+ }
+
+ /* Microsoft's WoF driver errors out if it tries to satisfy a read with
+ * ending offset >= 4 GiB from an externally backed file. */
+ if (rdesc->uncompressed_size > 4200000000) {
+ ctx->wimboot.have_huge_resources = true;
+ return false;
+ }
+
+ return true;
+}
+