Re: [PATCH 3/5] tools/vhost-user-i2c: Add backend driver

[Viresh Kumar <viresh.kumar@linaro.org>]

On 25-03-21, 17:16, Arnd Bergmann wrote:
> On Wed, Mar 24, 2021 at 8:33 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
> > +static void vi2c_handle_ctrl(VuDev *dev, int qidx)
> > +{
> > +    VuVirtq *vq = vu_get_queue(dev, qidx);
> > +    struct i2c_msg msg;
> > +    struct virtio_i2c_out_hdr *out_hdr;
> > +    struct virtio_i2c_in_hdr *in_hdr;
> > +    bool fail_next = false;
> > +    size_t len, in_hdr_len;
> > +
> > +    for (;;) {
> > +        VuVirtqElement *elem;
> > +
> > +        elem = vu_queue_pop(dev, vq, sizeof(VuVirtqElement));
> > +        if (!elem) {
> > +            break;
> > +        }
> > +
> > +        g_debug("%s: got queue (in %d, out %d)", __func__, elem->in_num,
> > +                elem->out_num);
> > +
> > +        /* Validate size of out header */
> > +        if (elem->out_sg[0].iov_len != sizeof(*out_hdr)) {
> > +            g_warning("%s: Invalid out hdr %zu : %zu\n", __func__,
> > +                      elem->out_sg[0].iov_len, sizeof(*out_hdr));
> > +            continue;
> > +        }
> > +
> > +        out_hdr = elem->out_sg[0].iov_base;
> > +
> > +        /* Bit 0 is reserved in virtio spec */
> > +        msg.addr = out_hdr->addr >> 1;
> > +
> > +        /* Read Operation */
> > +        if (elem->out_num == 1 && elem->in_num == 2) {
> > +            len = elem->in_sg[0].iov_len;
> > +            if (!len) {
> > +                g_warning("%s: Read buffer length can't be zero\n", __func__);
> > +                continue;
> > +            }
> 
> 
> It looks like you are not handling endianness conversion here. As far as I
> can tell, the protocol requires little-endian data, but the code might
> run on a big-endian CPU.

I hope this is all we are required to do here, right ?

@@ -442,7 +421,7 @@ static void vi2c_handle_ctrl(VuDev *dev, int qidx)
         out_hdr = elem->out_sg[0].iov_base;
 
         /* Bit 0 is reserved in virtio spec */
-        msg.addr = out_hdr->addr >> 1;
+        msg.addr = le16toh(out_hdr->addr) >> 1;
 
         /* Read Operation */
         if (elem->out_num == 1 && elem->in_num == 2) {
@@ -489,7 +468,7 @@ static void vi2c_handle_ctrl(VuDev *dev, int qidx)
         in_hdr->status = fail_next ? VIRTIO_I2C_MSG_ERR : vi2c_xfer(dev, &msg);
         if (in_hdr->status == VIRTIO_I2C_MSG_ERR) {
             /* We need to fail remaining transfers as well */
-            fail_next = out_hdr->flags & VIRTIO_I2C_FLAGS_FAIL_NEXT;
+            fail_next = le32toh(out_hdr->flags) & VIRTIO_I2C_FLAGS_FAIL_NEXT;
         }
 
These are the only fields we are passing apart from buf, which goes
directly to the client device.

-- 
viresh