ec_sign_update
ATTRIBUTE_WARN_UNUSED_RET int ec_sign_update(struct ec_sign_context *ctx, const u8 *chunk, u32 chunklen);
ret = ec_sign_update(&ctx, m, mlen); EG(ret, err);
ret = ec_sign_update(&ctx, &m[consumed], toconsume);
ret = ec_sign_update(&sig_ctx, (const u8 *)&hdr, sizeof(metadata_hdr));
ret = ec_sign_update(&sig_ctx, buf, (u32)read);