Re: [Qemu-devel] [PATCH 5/5] qemu-ga: win32: add isa-serial support

[Luiz Capitulino]

On Thu, 1 Nov 2012 11:31:05 -0500
Michael Roth <address@hidden> wrote:

> On Wed, Oct 31, 2012 at 03:45:20PM -0200, Luiz Capitulino wrote:
> > It's implemented by opening the serial port in "non-blocking" mode
> > and using the GSourceFuncs API in the following way:
> > 
> >  o prepare(): issue a read request. If something has been read, it's
> >               stored in rs->buf and rs->pending will store the number
> >                       of bytes read. If there wasn't any bytes available, we
> >                       set the timeout to 500 ms and return
> > 
> >  o check():   returns true if prepare() was able to read anything,
> >               otherwise return false
> > 
> >  o finalize(): does nothing
> > 
> > At dispatch() time we simply copy the bytes read to the buffer passed
> > to ga_channel_read().
> > 
> > Signed-off-by: Luiz Capitulino <address@hidden>
> > ---
> >  qga/channel-win32.c | 87 
> > +++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 87 insertions(+)
> > 
> > diff --git a/qga/channel-win32.c b/qga/channel-win32.c
> > index c173270..887fe5f 100644
> > --- a/qga/channel-win32.c
> > +++ b/qga/channel-win32.c
> > @@ -179,6 +179,46 @@ static gboolean ga_channel_dispatch_ov(GSource 
> > *source, GSourceFunc unused,
> >      return success;
> >  }
> > 
> > +static gboolean ga_channel_prepare(GSource *source, gint *timeout_ms)
> > +{
> > +    GAWatch *watch = (GAWatch *)source;
> > +    GAChannel *c = (GAChannel *)watch->channel;
> > +    GAChannelReadState *rs = &c->rstate;
> > +    DWORD count_read = 0;
> > +    bool success;
> > +
> > +    success = ReadFile(c->handle, rs->buf, rs->buf_size, &count_read, 
> > NULL);
> > +    if (success) {
> > +        if (count_read == 0) {
> > +            *timeout_ms = 500;
> > +            return false;
> > +        }
> > +        rs->pending = count_read;
> > +        return true;
> > +    }
> > +
> > +    return false;
> > +}
> > +
> > +static gboolean ga_channel_check(GSource *source)
> > +{
> > +    GAWatch *watch = (GAWatch *)source;
> > +    GAChannel *c = (GAChannel *)watch->channel;
> > +    GAChannelReadState *rs = &c->rstate;
> > +
> > +    return !!rs->pending;
> > +}
> > +
> > +static gboolean ga_channel_dispatch(GSource *source, GSourceFunc unused,
> > +                                    gpointer user_data)
> > +{
> > +    GAWatch *watch = (GAWatch *)source;
> > +    GAChannel *c = (GAChannel *)watch->channel;
> > +
> > +    g_assert(c->cb);
> > +    return c->cb(0, c->user_data);
> > +}
> > +
> >  static void ga_channel_finalize_ov(GSource *source)
> >  {
> >      g_debug("finalize");
> > @@ -203,6 +243,30 @@ static GSource *ga_channel_create_watch_ov(GAChannel 
> > *c)
> >      return source;
> >  }
> > 
> > +static void ga_channel_finalize(GSource *source)
> > +{
> > +    g_debug("finalize");
> > +}
> > +
> > +GSourceFuncs ga_channel_watch_funcs = {
> > +    ga_channel_prepare,
> > +    ga_channel_check,
> > +    ga_channel_dispatch,
> > +    ga_channel_finalize
> > +};
> > +
> > +static GSource *ga_channel_create_watch(GAChannel *c)
> > +{
> > +    GSource *source = g_source_new(&ga_channel_watch_funcs, 
> > sizeof(GAWatch));
> > +    GAWatch *watch = (GAWatch *)source;
> > +
> > +    watch->channel = c;
> > +    watch->pollfd.fd = -1;
> > +    g_source_add_poll(source, &watch->pollfd);
> > +
> > +    return source;
> > +}
> > +
> >  GIOStatus ga_channel_read(GAChannel *c, char *buf, size_t size, gsize 
> > *count)
> >  {
> >      GAChannelReadState *rs = &c->rstate;
> > @@ -225,6 +289,12 @@ GIOStatus ga_channel_read(GAChannel *c, char *buf, 
> > size_t size, gsize *count)
> >              status = G_IO_STATUS_AGAIN;
> >          }
> >          break;
> > +    case GA_CHANNEL_ISA_SERIAL:
> > +        memcpy(buf, rs->buf, rs->pending);
> 
> Do we really want to ignore size? Seems like we can overrun their buffer
> if it's smaller than ours. You can use rs->start to track the number of
> bytes theyve read so far and offset from that in prepare()

size == rs->buf_size, so we're ok. Although this is sensible, as both buffers
are not tied...

I think that the intermediate buffer handling complicate things, and for
isa-serial this is not needed. What about returning the buffer from
ga_channel_read()?

I mean, instead of:

gchar buf[QGA_READ_COUNT_DEFAULT+1];
gsize count;
...

ga_channel_read(s->channel, buf, QGA_READ_COUNT_DEFAULT, &count);

We could have:

gchar *buf;
gsize count;
...

ga_channel_read(s->channel, &buf, &count);

> 
> > +        *count = rs->pending;
> > +        rs->pending = 0;
> > +        status = G_IO_STATUS_NORMAL;
> > +        break;
> >      default:
> >          abort(); /* impossible */
> >      }
> > @@ -303,6 +373,7 @@ GAChannel *ga_channel_new(GAChannelMethod method, const 
> > gchar *path,
> >  {
> >      GAChannel *c = g_malloc0(sizeof(GAChannel));
> >      SECURITY_ATTRIBUTES sec_attrs;
> > +    COMMTIMEOUTS timeouts;
> > 
> >      switch (method) {
> >      case GA_CHANNEL_VIRTIO_SERIAL:
> > @@ -322,6 +393,22 @@ GAChannel *ga_channel_new(GAChannelMethod method, 
> > const gchar *path,
> > 
> >          c->source = ga_channel_create_watch_ov(c);
> >          break;
> > +    case GA_CHANNEL_ISA_SERIAL:
> > +        if (!ga_channel_open(c, path, 0)) {
> > +            g_critical("error opening channel (path: %s)", path);
> > +            goto out_err;
> > +        }
> > +
> > +        /* non-blocking I/O */
> > +        memset(&timeouts, 0, sizeof(timeouts));
> > +        timeouts.ReadIntervalTimeout = MAXDWORD;
> > +        if (!SetCommTimeouts(c->handle, &timeouts)) {
> > +            CloseHandle(c->handle);
> > +            goto out_err;
> > +        }
> > +
> > +        c->source = ga_channel_create_watch(c);
> > +        break;
> >      default:
> >          g_critical("unsupported communication method");
> >          goto out_err;
> > -- 
> > 1.7.12.315.g682ce8b
> > 
> > 
>