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Re: [Qemu-devel] [PATCH 5/5] qemu-ga: win32: add isa-serial support
From: |
Luiz Capitulino |
Subject: |
Re: [Qemu-devel] [PATCH 5/5] qemu-ga: win32: add isa-serial support |
Date: |
Thu, 1 Nov 2012 17:33:24 -0200 |
On Thu, 1 Nov 2012 14:13:52 -0500
Michael Roth <address@hidden> wrote:
> On Thu, Nov 01, 2012 at 02:55:20PM -0200, Luiz Capitulino wrote:
> > 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...
>
> Hmm, true. But there's no contract that users of ga_channel_read() have to
> use size==QGA_READ_COUNT_DEFAULT, so this could cause problems if that
> ever changed.
That's correct.
>
> >
> > 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);
>
> We don't expose our internal buffer for virtio-serial because if it
> fills up, and there were partial reads (which might occur if size !=
> QGA_READ_COUNT_DEFAULT) there may be unused space at the beginning of
> the buffer, so we'll shift the used portion back to the beginning to
> read as much as possible for each IO request. It's minor optimization,
> but only requires a few lines of code to implement so I think it makes
> sense. So that prevents us from passing the buffer directly to users
> in that case.
I meant to do that only for isa-serial, but what you suggest below is better.
> If we want to avoid this for isa-serial, I'd avoiding the use of the
> internal buffer completely. What you might be able to do instead is:
>
> - have your prepare() function call ClearCommError(), then check the returned
> lpStat information for the cbInQue value, which will give you the number of
> bytes available. If it's > 0, prepare() can set c->pending to this
> amount, and avoid the ReadFile() or using the internal buffer.
I can't tell you how much time I spent looking for a function that would
give me that info! This is really the right of of implementing this.
> - in ga_channel_read(), you can read MIN(size, c->pending) bytes directly
> into the buf it's called with via ReadFile().
>
> >
> > >
> > > > + *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
> > > >
> > > >
> > >
> >
> >
>