Patchwork [15/17] virtio-serial: Apps should consume all data that guest sends out / Fix virtio api abuse

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Submitter Amit Shah
Date March 31, 2010, 7:34 a.m.
Message ID <1270020848-15526-16-git-send-email-amit.shah@redhat.com>
Download mbox | patch
Permalink /patch/49095/
State New
Headers show

Comments

Amit Shah - March 31, 2010, 7:34 a.m.
We cannot indicate to the guest how much data was consumed by an app for
out_bufs.  So we just have to assume the apps will consume all the data
that are handed over to them.

Fix the virtio api abuse in control_out() and handle_output().

Signed-off-by: Amit Shah <amit.shah@redhat.com>
---
 hw/virtio-console.c    |    7 ++-----
 hw/virtio-serial-bus.c |    6 +++---
 hw/virtio-serial.h     |    6 +++---
 3 files changed, 8 insertions(+), 11 deletions(-)
Gerd Hoffmann - March 31, 2010, 1:53 p.m.
>   /* Callback function that's called when the guest sends us data */
> -static size_t flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
> +static void flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
>   {
>       VirtConsole *vcon = DO_UPCAST(VirtConsole, port, port);
> -    ssize_t ret;
>
> -    ret = qemu_chr_write(vcon->chr, buf, len);
> -
> -    return ret<  0 ? 0 : ret;
> +    qemu_chr_write(vcon->chr, buf, len);
>   }

Ok, so we loose data in case qemu_chr_write wasn't able to write out all 
data?  Nice opportunity to show flow control in action here ;)

On failed+partial writes just put the remaining data into a buffer and 
throttle the port until all buffered data has been successfully written 
to the chardev.

Incremental patch is fine to avoid the chicken-egg issue (throttling is 
added by patch #17).

cheers,
   Gerd
Amit Shah - March 31, 2010, 2:06 p.m.
On (Wed) Mar 31 2010 [15:53:59], Gerd Hoffmann wrote:
>>   /* Callback function that's called when the guest sends us data */
>> -static size_t flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
>> +static void flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
>>   {
>>       VirtConsole *vcon = DO_UPCAST(VirtConsole, port, port);
>> -    ssize_t ret;
>>
>> -    ret = qemu_chr_write(vcon->chr, buf, len);
>> -
>> -    return ret<  0 ? 0 : ret;
>> +    qemu_chr_write(vcon->chr, buf, len);
>>   }
>
> Ok, so we loose data in case qemu_chr_write wasn't able to write out all  
> data?  Nice opportunity to show flow control in action here ;)
>
> On failed+partial writes just put the remaining data into a buffer and  
> throttle the port until all buffered data has been successfully written  
> to the chardev.
>
> Incremental patch is fine to avoid the chicken-egg issue (throttling is  
> added by patch #17).

Yes, that's what I intend to do in a later patch (series).

		Amit

Patch

diff --git a/hw/virtio-console.c b/hw/virtio-console.c
index bbbb6b8..caea11f 100644
--- a/hw/virtio-console.c
+++ b/hw/virtio-console.c
@@ -20,14 +20,11 @@  typedef struct VirtConsole {
 
 
 /* Callback function that's called when the guest sends us data */
-static size_t flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
+static void flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
 {
     VirtConsole *vcon = DO_UPCAST(VirtConsole, port, port);
-    ssize_t ret;
 
-    ret = qemu_chr_write(vcon->chr, buf, len);
-
-    return ret < 0 ? 0 : ret;
+    qemu_chr_write(vcon->chr, buf, len);
 }
 
 /* Readiness of the guest to accept data on a port */
diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
index 49a6baa..7ac46f5 100644
--- a/hw/virtio-serial-bus.c
+++ b/hw/virtio-serial-bus.c
@@ -336,7 +336,7 @@  static void control_out(VirtIODevice *vdev, VirtQueue *vq)
         copied = iov_to_buf(elem.out_sg, elem.out_num, buf, 0, len);
 
         handle_control_message(vser, buf, copied);
-        virtqueue_push(vq, &elem, copied);
+        virtqueue_push(vq, &elem, 0);
     }
     if (len) {
         qemu_free(buf);
@@ -382,11 +382,11 @@  static void handle_output(VirtIODevice *vdev, VirtQueue *vq)
         buf = qemu_malloc(buf_size);
         ret = iov_to_buf(elem.out_sg, elem.out_num, buf, 0, buf_size);
 
-        ret = port->info->have_data(port, buf, ret);
+        port->info->have_data(port, buf, ret);
         qemu_free(buf);
 
     next_buf:
-        virtqueue_push(vq, &elem, ret);
+        virtqueue_push(vq, &elem, 0);
     }
     virtio_notify(vdev, vq);
 }
diff --git a/hw/virtio-serial.h b/hw/virtio-serial.h
index f023873..62d76a2 100644
--- a/hw/virtio-serial.h
+++ b/hw/virtio-serial.h
@@ -136,10 +136,10 @@  struct VirtIOSerialPortInfo {
 
     /*
      * Guest wrote some data to the port. This data is handed over to
-     * the app via this callback. The app should return the number of
-     * bytes it successfully consumed.
+     * the app via this callback.  The app is supposed to consume all
+     * the data that is presented to it.
      */
-    size_t (*have_data)(VirtIOSerialPort *port, const uint8_t *buf, size_t len);
+    void (*have_data)(VirtIOSerialPort *port, const uint8_t *buf, size_t len);
 };
 
 /* Interface to the virtio-serial bus */