On Thu 02 Apr 2020 08:36:44 AM CEST, Denis Plotnikov wrote:
> +static ssize_t qcow2_zstd_compress(void *dest, size_t dest_size,
> + const void *src, size_t src_size)
> +{
> + ssize_t ret;
> + ZSTD_outBuffer output = { dest, dest_size, 0 };
> + ZSTD_inBuffer input = { src, src_size, 0 };
> + ZSTD_CCtx *cctx = ZSTD_createCCtx();
> +
> + if (!cctx) {
> + return -EIO;
> + }
> + /*
> + * Use the zstd streamed interface for symmetry with decompression,
> + * where streaming is essential since we don't record the exact
> + * compressed size.
> + *
> + * In the loop, we try to compress all the data into one zstd frame.
> + * ZSTD_compressStream2 potentially can finish a frame earlier
> + * than the full input data is consumed. That's why we are looping
> + * until all the input data is consumed.
> + */
> + while (input.pos < input.size) {
> + size_t zstd_ret;
> + /*
> + * ZSTD spec: "You must continue calling ZSTD_compressStream2()
> + * with ZSTD_e_end until it returns 0, at which point you are
> + * free to start a new frame". We assume that "start a new frame"
> + * means call ZSTD_compressStream2 in the very beginning or when
> + * ZSTD_compressStream2 has returned with 0.
> + */
> + do {
> + zstd_ret = ZSTD_compressStream2(cctx, &output, &input,
> ZSTD_e_end);
> +
> + if (ZSTD_isError(zstd_ret)) {
> + ret = -EIO;
> + goto out;
> + }
> + /* Dest buffer isn't big enough to store compressed content */
> + if (zstd_ret > output.size - output.pos) {
> + ret = -ENOMEM;
> + goto out;
> + }
> + } while (zstd_ret);
> + }
> + /* make sure we can safely return compressed buffer size with ssize_t */
> + assert(output.pos <= SSIZE_MAX);
The patch looks good to me, but why don't you assert this at the
beginning of the function? You already know the buffer sizes...
Either way,
Reviewed-by: Alberto Garcia <be...@igalia.com>
Berto
