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exanic: avoid receiving corrupted frames when lapped during memcpy #44

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exanic: avoid receiving corrupted frames when lapped during memcpy #44

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68 changes: 55 additions & 13 deletions libs/exanic/fifo_rx.c
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Original file line number Diff line number Diff line change
Expand Up @@ -308,12 +308,16 @@ void __exanic_rx_catchup(exanic_rx_t *rx)
if (eof_found)
{
/* Set next_chunk to the chunk after the most recent end-of-frame */
rx->sentinel_chunk = eof_chunk;
rx->sentinel_chunk_generation = eof_gen;
rx->next_chunk = eof_chunk + 1;
rx->generation = eof_gen;
}
else
{
/* Set next_chunk to where generation number changes */
rx->sentinel_chunk = break_chunk;
rx->sentinel_chunk_generation = break_gen;
rx->next_chunk = break_chunk + 1;
rx->generation = break_gen;
}
Expand All @@ -339,10 +343,11 @@ ssize_t exanic_receive_frame(exanic_rx_t *rx, char *rx_buf, size_t rx_buf_size,
{
size_t size = 0;

/* Next expected packet */
/* Next expected chunk */
while (1)
{
const char *payload = (char *)rx->buffer[rx->next_chunk].payload;
uint32_t current_chunk = rx->next_chunk;
const char *payload = (char *)rx->buffer[current_chunk].payload;

/* Advance next_chunk to next chunk */
rx->next_chunk++;
Expand All @@ -360,9 +365,22 @@ ssize_t exanic_receive_frame(exanic_rx_t *rx, char *rx_buf, size_t rx_buf_size,
return -EXANIC_RX_FRAME_TRUNCATED;

memcpy(rx_buf + size, payload, u.info.length);
size += u.info.length;

/* TODO: Recheck that we haven't been lapped */
/* Move the sentinel chunk forward. */
uint32_t sentinel_chunk = rx->sentinel_chunk;
uint8_t sentinel_chunk_generation = rx->sentinel_chunk_generation;
rx->sentinel_chunk = current_chunk;
rx->sentinel_chunk_generation = u.info.generation;

/* Check that we couldn't have gotten lapped during memcpy. */
if (rx->buffer[sentinel_chunk].u.info.generation !=
sentinel_chunk_generation)
{
__exanic_rx_catchup(rx);
return -EXANIC_RX_FRAME_SWOVFL;
}

size += u.info.length;

if (timestamp != NULL)
*timestamp = u.info.timestamp;
Expand All @@ -384,13 +402,6 @@ ssize_t exanic_receive_frame(exanic_rx_t *rx, char *rx_buf, size_t rx_buf_size,
do
u.data = rx->buffer[rx->next_chunk].u.data;
while (u.info.generation == (uint8_t)(rx->generation - 1));

if (u.info.generation != rx->generation)
{
/* Got lapped? */
__exanic_rx_catchup(rx);
return -EXANIC_RX_FRAME_SWOVFL;
}
}
}
}
Expand Down Expand Up @@ -418,6 +429,12 @@ ssize_t exanic_receive_chunk(exanic_rx_t *rx, char *rx_buf, int *more_chunks)

if (u.info.generation == rx->generation)
{
/* Move the sentinel chunk forward. */
uint32_t sentinel_chunk = rx->sentinel_chunk;
uint8_t sentinel_chunk_generation = rx->sentinel_chunk_generation;
rx->sentinel_chunk = rx->next_chunk;
rx->sentinel_chunk_generation = u.info.generation;

/* Data is available */
const char *payload = (char *)rx->buffer[rx->next_chunk].payload;

Expand All @@ -434,7 +451,12 @@ ssize_t exanic_receive_chunk(exanic_rx_t *rx, char *rx_buf, int *more_chunks)
/* Last chunk */
memcpy(rx_buf, payload, u.info.length);

/* TODO: Recheck that we haven't been lapped */
/* Check that we couldn't have gotten lapped during memcpy. */
if (rx->buffer[sentinel_chunk].u.info.generation != sentinel_chunk_generation)
{
__exanic_rx_catchup(rx);
return -EXANIC_RX_FRAME_SWOVFL;
}

if (u.info.frame_status & EXANIC_RX_FRAME_ERROR_MASK)
return -(u.info.frame_status & EXANIC_RX_FRAME_ERROR_MASK);
Expand All @@ -447,6 +469,13 @@ ssize_t exanic_receive_chunk(exanic_rx_t *rx, char *rx_buf, int *more_chunks)
/* More chunks to come */
memcpy(rx_buf, payload, EXANIC_RX_CHUNK_PAYLOAD_SIZE);

/* Check that we couldn't have gotten lapped during memcpy. */
if (rx->buffer[sentinel_chunk].u.info.generation != sentinel_chunk_generation)
{
__exanic_rx_catchup(rx);
return -EXANIC_RX_FRAME_SWOVFL;
}

*more_chunks = 1;
return EXANIC_RX_CHUNK_PAYLOAD_SIZE;
}
Expand Down Expand Up @@ -476,6 +505,12 @@ ssize_t exanic_receive_chunk_ex(exanic_rx_t *rx, char *rx_buf, int *more_chunks,

if (u.info.generation == rx->generation)
{
/* Move the sentinel chunk forward. */
uint32_t sentinel_chunk = rx->sentinel_chunk;
uint8_t sentinel_chunk_generation = rx->sentinel_chunk_generation;
rx->sentinel_chunk = rx->next_chunk;
rx->sentinel_chunk_generation = u.info.generation;

/* Data is available */
const char *payload = (char *)rx->buffer[rx->next_chunk].payload;
uint8_t length;
Expand All @@ -492,7 +527,14 @@ ssize_t exanic_receive_chunk_ex(exanic_rx_t *rx, char *rx_buf, int *more_chunks,
more = (u.info.length == 0);
length = more ? EXANIC_RX_CHUNK_PAYLOAD_SIZE : u.info.length;
memcpy(rx_buf, payload, length);
/* TODO: Recheck that we haven't been lapped */

/* Check that we couldn't have gotten lapped during memcpy. */
if (rx->buffer[sentinel_chunk].u.info.generation != sentinel_chunk_generation)
{
__exanic_rx_catchup(rx);
return -EXANIC_RX_FRAME_SWOVFL;
}

*more_chunks = more;
*info = u.info;
return length;
Expand Down
2 changes: 2 additions & 0 deletions libs/exanic/fifo_rx.h
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,8 @@ typedef struct exanic_rx
int port_number;
int buffer_number;
volatile struct rx_chunk *buffer;
uint32_t sentinel_chunk;
uint8_t sentinel_chunk_generation;
uint32_t next_chunk;
uint8_t generation;
} exanic_rx_t;
Expand Down