}
+static ssize_t qcrypto_block_headerlen_hdr_init_func(QCryptoBlock *block,
+ size_t headerlen, void *opaque, Error **errp)
+{
+ size_t *headerlenp = opaque;
+
+ /* Stash away the payload size */
+ *headerlenp = headerlen;
+ return 0;
+}
+
+
+static ssize_t qcrypto_block_headerlen_hdr_write_func(QCryptoBlock *block,
+ size_t offset, const uint8_t *buf, size_t buflen,
+ void *opaque, Error **errp)
+{
+ /* Discard the bytes, we're not actually writing to an image */
+ return buflen;
+}
+
+
+bool
+qcrypto_block_calculate_payload_offset(QCryptoBlockCreateOptions *create_opts,
+ const char *optprefix,
+ size_t *len,
+ Error **errp)
+{
+ /* Fake LUKS creation in order to determine the payload size */
+ g_autoptr(QCryptoBlock) crypto =
+ qcrypto_block_create(create_opts, optprefix,
+ qcrypto_block_headerlen_hdr_init_func,
+ qcrypto_block_headerlen_hdr_write_func,
+ len, errp);
+ return crypto != NULL;
+}
+
+int qcrypto_block_amend_options(QCryptoBlock *block,
+ QCryptoBlockReadFunc readfunc,
+ QCryptoBlockWriteFunc writefunc,
+ void *opaque,
+ QCryptoBlockAmendOptions *options,
+ bool force,
+ Error **errp)
+{
+ if (options->format != block->format) {
+ error_setg(errp,
+ "Cannot amend encryption format");
+ return -1;
+ }
+
+ if (!block->driver->amend) {
+ error_setg(errp,
+ "Crypto format %s doesn't support format options amendment",
+ QCryptoBlockFormat_str(block->format));
+ return -1;
+ }
+
+ return block->driver->amend(block,
+ readfunc,
+ writefunc,
+ opaque,
+ options,
+ force,
+ errp);
+}
+
QCryptoBlockInfo *qcrypto_block_get_info(QCryptoBlock *block,
Error **errp)
{