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connection: empty iovecs are never created

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Neither ring_buffer_put_iov() nor ring_buffer_get_iov() distinguishes
between a full wl_ring_buffer and an empty one.  Instead, both just
assume that the returned iovec should not be empty.  However, both have
only one caller, and that caller does guarantee that the ring buffer is
not full (for ring_buffer_put_iov()) or empty (for
ring_buffer_get_iov()).  Therefore, the code is safe.

Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
This commit is contained in:
Demi Marie Obenour 2024-07-29 15:27:21 -04:00
parent f00586ee5f
commit 568a9325f0
1 changed files with 10 additions and 0 deletions
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10
src/connection.c
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@ -113,6 +113,7 @@ ring_buffer_put(struct wl_ring_buffer *b, const void *data, size_t count)
return 0;
}
/* Precondition: the buffer is not full */
static void
ring_buffer_put_iov(struct wl_ring_buffer *b, struct iovec *iov, int *count)
{
@ -125,10 +126,13 @@ ring_buffer_put_iov(struct wl_ring_buffer *b, struct iovec *iov, int *count)
iov[0].iov_len = tail - head;
*count = 1;
} else if (tail == 0) {
/* We assume that head == 0 means an empty buffer, not a full one. */
iov[0].iov_base = b->data + head;
iov[0].iov_len = ring_buffer_capacity(b) - head;
*count = 1;
} else {
/* head == 0 is checked earlier, so there is at least one byte to
* read after head. */
iov[0].iov_base = b->data + head;
iov[0].iov_len = ring_buffer_capacity(b) - head;
iov[1].iov_base = b->data;
@ -137,6 +141,7 @@ ring_buffer_put_iov(struct wl_ring_buffer *b, struct iovec *iov, int *count)
}
}
/* Precondition: the buffer is not empty */
static void
ring_buffer_get_iov(struct wl_ring_buffer *b, struct iovec *iov, int *count)
{
@ -161,6 +166,7 @@ ring_buffer_get_iov(struct wl_ring_buffer *b, struct iovec *iov, int *count)
}
}
/* Precondition: the data will not overflow the buffer */
static void
ring_buffer_copy(struct wl_ring_buffer *b, void *data, size_t count)
{
@ -456,6 +462,9 @@ wl_connection_flush(struct wl_connection *connection)
tail = connection->out.tail;
while (ring_buffer_size(&connection->out) > 0) {
/* Ring buffer is not empty, so this is safe. */
ring_buffer_get_iov(&connection->out, iov, &count);
build_cmsg(&connection->fds_out, cmsg, &clen);
if (clen >= CLEN) {
@ -530,6 +539,7 @@ wl_connection_read(struct wl_connection *connection)
if (ring_buffer_ensure_space(&connection->in, 1) < 0)
return -1;
/* Ring buffer is not full, so this is safe. */
ring_buffer_put_iov(&connection->in, iov, &count);
msg.msg_name = NULL;