On (Wed) Dec 02 2009 [14:14:20], Rusty Russell wrote:
> On Sat, 28 Nov 2009 05:20:35 pm Amit Shah wrote:
> > The console could be flooded with data from the host; handle
> > this situation by buffering the data.
>
> All this complexity makes me really wonder if we should just
> have the host say the max # ports it will ever use, and just do this
> really dumbly. Yes, it's a limitation, but it'd be much simpler.
As in make sure the max nr ports is less than 255 and have per-port vqs?
And then the buffering will be done inside the vqs themselves?
> > --- a/drivers/char/virtio_console.c
> > +++ b/drivers/char/virtio_console.c
> > @@ -65,6 +65,23 @@ struct ports_device {
> > * interrupt
> > */
> > struct work_struct rx_work;
> > +
> > + struct list_head unused_read_head;
>
> You should name lists after plurals, rather than using "head" which is
> an implementation detail. eg. "queued_inbufs" and below "used_inbufs".
OK.
> Though Shirly Ma was working on a "destroy_bufs" patch which would avoid
> your need for this list at all, AFAICT.
>
> > + /* Return the number of bytes actually copied */
> > + ret = copy_size;
> > + buf->offset += ret;
> > + out_offset += ret;
> > + out_count -= ret;
>
> We don't actually use ret.
In a later patch, when copy_to_user is added, ret will be used. So I
kept it this way to reduce the noise in the diffs later.
> > + if (buf->len - buf->offset == 0) {
>
> I prefer the simpler "if (buf->offset == buf->len)" myself.
Will update.
> > + spin_lock_irqsave(&port->readbuf_list_lock, flags);
> > + list_del(&buf->list);
> > + spin_unlock_irqrestore(&port->readbuf_list_lock, flags);
> > + kfree(buf->buf);
> > + kfree(buf);
>
> Does it become cleaner later to have this in a separate function? Usually
> I prefer matching alloc and free fns.
Adding a function is easy, sure. I should've done that though; something
that got overlooked.
> > +static struct port_buffer *get_buf(size_t buf_size)
> > +{
> > + struct port_buffer *buf;
> > +
> > + buf = kzalloc(sizeof(*buf), GFP_KERNEL);
> > + if (!buf)
> > + goto out;
> > + buf->buf = kzalloc(buf_size, GFP_KERNEL);
> > + if (!buf->buf) {
> > + kfree(buf);
> > + goto out;
>
> No, that would return non-NULL. I'd stick with the standard multi-part exit:
>
> if (!buf)
> goto fail;
> buf->buf = kzalloc(buf_size, GFP_KERNEL);
> if (!buf->buf)
> goto fail_free_buf;
> buf->len = buf_size;
> return buf;
>
> fail_free_buf:
> kfree(buf);
> fail:
> return NULL;
Ow, indeed.
Thanks!
Amit
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