diff --git a/include/qemu/fifo8.h b/include/qemu/fifo8.h index 16be02f361..c6295c6ff0 100644 --- a/include/qemu/fifo8.h +++ b/include/qemu/fifo8.h @@ -71,7 +71,7 @@ uint8_t fifo8_pop(Fifo8 *fifo); * fifo8_pop_buf: * @fifo: FIFO to pop from * @max: maximum number of bytes to pop - * @num: actual number of returned bytes + * @numptr: pointer filled with number of bytes returned (can be NULL) * * Pop a number of elements from the FIFO up to a maximum of max. The buffer * containing the popped data is returned. This buffer points directly into @@ -82,16 +82,43 @@ uint8_t fifo8_pop(Fifo8 *fifo); * around in the ring buffer; in this case only a contiguous part of the data * is returned. * - * The number of valid bytes returned is populated in *num; will always return - * at least 1 byte. max must not be 0 or greater than the number of bytes in - * the FIFO. + * The number of valid bytes returned is populated in *numptr; will always + * return at least 1 byte. max must not be 0 or greater than the number of + * bytes in the FIFO. * * Clients are responsible for checking the availability of requested data * using fifo8_num_used(). * * Returns: A pointer to popped data. */ -const uint8_t *fifo8_pop_buf(Fifo8 *fifo, uint32_t max, uint32_t *num); +const uint8_t *fifo8_pop_buf(Fifo8 *fifo, uint32_t max, uint32_t *numptr); + +/** + * fifo8_peek_buf: read upto max bytes from the fifo + * @fifo: FIFO to read from + * @max: maximum number of bytes to peek + * @numptr: pointer filled with number of bytes returned (can be NULL) + * + * Peek into a number of elements from the FIFO up to a maximum of max. + * The buffer containing the data peeked into is returned. This buffer points + * directly into the FIFO backing store. Since data is invalidated once any + * of the fifo8_* APIs are called on the FIFO, it is the caller responsibility + * to access it before doing further API calls. + * + * The function may return fewer bytes than requested when the data wraps + * around in the ring buffer; in this case only a contiguous part of the data + * is returned. + * + * The number of valid bytes returned is populated in *numptr; will always + * return at least 1 byte. max must not be 0 or greater than the number of + * bytes in the FIFO. + * + * Clients are responsible for checking the availability of requested data + * using fifo8_num_used(). + * + * Returns: A pointer to peekable data. + */ +const uint8_t *fifo8_peek_buf(Fifo8 *fifo, uint32_t max, uint32_t *numptr); /** * fifo8_reset: diff --git a/util/fifo8.c b/util/fifo8.c index de8fd0f1c5..4e01b532d9 100644 --- a/util/fifo8.c +++ b/util/fifo8.c @@ -66,19 +66,37 @@ uint8_t fifo8_pop(Fifo8 *fifo) return ret; } -const uint8_t *fifo8_pop_buf(Fifo8 *fifo, uint32_t max, uint32_t *num) +static const uint8_t *fifo8_peekpop_buf(Fifo8 *fifo, uint32_t max, + uint32_t *numptr, bool do_pop) { uint8_t *ret; + uint32_t num; assert(max > 0 && max <= fifo->num); - *num = MIN(fifo->capacity - fifo->head, max); + num = MIN(fifo->capacity - fifo->head, max); ret = &fifo->data[fifo->head]; - fifo->head += *num; - fifo->head %= fifo->capacity; - fifo->num -= *num; + + if (do_pop) { + fifo->head += num; + fifo->head %= fifo->capacity; + fifo->num -= num; + } + if (numptr) { + *numptr = num; + } return ret; } +const uint8_t *fifo8_peek_buf(Fifo8 *fifo, uint32_t max, uint32_t *numptr) +{ + return fifo8_peekpop_buf(fifo, max, numptr, false); +} + +const uint8_t *fifo8_pop_buf(Fifo8 *fifo, uint32_t max, uint32_t *numptr) +{ + return fifo8_peekpop_buf(fifo, max, numptr, true); +} + void fifo8_reset(Fifo8 *fifo) { fifo->num = 0;