On Mon, 21 Mar 2011 15:52:25 +0000
Toby Gray <toby.gray@xxxxxxxxxxx> wrote:
> When sending large quantities of data through a CDC ACM channel it is possible
> for data to be lost when attempting to copy the data to the tty buffer. This
> occurs due to the return value from tty_insert_flip_string not being checked.
For a tty that is normally the right thing to do - no flow control was
asserted and the internal 64K of buffering was overrun so discard.
> This patch adds checking for how many bytes have been inserted into the tty
> buffer and returns any remaining bytes back to the filled read buffer list.
How does ACM handle flow control - is the expectation that it gets flow
controlled in hardware by not having the opportunity to send bits
to the host end ? If so this seems to make sense.
> + copied = 0;
Surely copied = buf->size is the no tty assumption "we had the lot and
discarded it"
> if (tty) {
> spin_lock_irqsave(&acm->throttle_lock, flags);
> throttled = acm->throttle;
> spin_unlock_irqrestore(&acm->throttle_lock, flags);
> if (!throttled) {
> - tty_insert_flip_string(tty, buf->base, buf->size);
> + copied = tty_insert_flip_string(tty,
> + buf->base, buf->size);
> tty_flip_buffer_push(tty);
> } else {
> tty_kref_put(tty);
> @@ -440,9 +443,26 @@ next_buffer:
> }
> }
>
> - spin_lock_irqsave(&acm->read_lock, flags);
> - list_add(&buf->list, &acm->spare_read_bufs);
> - spin_unlock_irqrestore(&acm->read_lock, flags);
> + if (copied == buf->size || !tty) {
Which would simplify this lot
> + spin_lock_irqsave(&acm->read_lock, flags);
> + list_add(&buf->list, &acm->spare_read_bufs);
> + spin_unlock_irqrestore(&acm->read_lock, flags);
> + } else {
> + tty_kref_put(tty);
> + dbg("Partial buffer fill");
> + if (copied > 0) {
> + memmove(buf->base,
> + buf->base + copied,
> + buf->size - copied);
> + buf->size -= copied;
> + }
Would it not be cleaner to add a buf->head pointer that could simply be
advanced so the code would become
buf->head += copied;
buf->size -= copied;
if (buf->size != 0)
list_add(&buf->list, &acm->filled_read_bufs);
instead of all the memmove uglies ?
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