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Subject: virtio_console: Fix poll blocking even though there is data to read (version 2)
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From: Hans de Goede <hdegoede@redhat.com>
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I found this while working on a Linux agent for spice, the symptom I was
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seeing was select blocking on the spice vdagent virtio serial port even
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though there were messages queued up there.
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virtio_console's port_fops_poll checks port->inbuf != NULL to determine if
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read won't block. However if an application reads enough bytes from inbuf
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through port_fops_read, to empty the current port->inbuf, port->inbuf
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will be NULL even though there may be buffers left in the virtqueue.
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This causes poll() to block even though there is data ready to be read, this
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patch fixes this by using port_has_data(port) instead of the
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port->inbuf != NULL check.
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Signed-off-By: Hans de Goede <hdegoede@redhat.com>
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diff -up linux-2.6.35.x86_64/drivers/char/virtio_console.c~ linux-2.6.35.x86_64/drivers/char/virtio_console.c
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--- linux-2.6.35.x86_64/drivers/char/virtio_console.c~ 2010-08-02 00:11:14.000000000 +0200
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+++ linux-2.6.35.x86_64/drivers/char/virtio_console.c 2010-09-15 13:39:29.043505000 +0200
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@@ -642,7 +642,7 @@ static unsigned int port_fops_poll(struc
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poll_wait(filp, &port->waitqueue, wait);
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ret = 0;
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- if (port->inbuf)
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+ if (port_has_data(port))
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ret |= POLLIN | POLLRDNORM;
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if (!will_write_block(port))
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ret |= POLLOUT;
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