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Date:   Tue, 1 Dec 2020 11:52:50 +0100
From:   Stefano Garzarella <sgarzare@redhat.com>
To:     Jason Wang <jasowang@redhat.com>
Cc:     virtualization@lists.linux-foundation.org,
        Stefan Hajnoczi <stefanha@redhat.com>,
        linux-kernel@vger.kernel.org, Laurent Vivier <lvivier@redhat.com>,
        Max Gurtovoy <mgurtovoy@nvidia.com>,
        "Michael S. Tsirkin" <mst@redhat.com>, Eli Cohen <elic@nvidia.com>
Subject: Re: [PATCH v2 12/17] vdpa_sim: add get_config callback in
 vdpasim_dev_attr
Message-ID: <20201201105250.a72yxsxmyalio6c3@steredhat>
References: <20201126144950.92850-1-sgarzare@redhat.com>
 <20201126144950.92850-13-sgarzare@redhat.com>
 <f8106986-e19d-ea32-436c-14cddd2b6ff4@redhat.com>
 <20201130141453.jobe76loyfy4qrdw@steredhat>
 <c2158059-6509-7702-f52a-e497ce899293@redhat.com>
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On Tue, Dec 01, 2020 at 11:44:19AM +0800, Jason Wang wrote:
>
>On 2020/11/30 下午10:14, Stefano Garzarella wrote:
>>On Mon, Nov 30, 2020 at 11:25:31AM +0800, Jason Wang wrote:
>>>
>>>On 2020/11/26 下午10:49, Stefano Garzarella wrote:
>>>>The get_config callback can be used by the device to fill the
>>>>config structure.
>>>>The callback will be invoked in vdpasim_get_config() before copying
>>>>bytes into caller buffer.
>>>>
>>>>Move vDPA-net config updates from vdpasim_set_features() in the
>>>>new vdpasim_net_get_config() callback.
>>>>
>>>>Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
>>>>---
>>>> drivers/vdpa/vdpa_sim/vdpa_sim.c | 33 +++++++++++++++++++-------------
>>>> 1 file changed, 20 insertions(+), 13 deletions(-)
>>>>
>>>>diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c 
>>>>b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>>>>index c07ddf6af720..8b87ce0485b6 100644
>>>>--- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
>>>>+++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>>>>@@ -58,6 +58,8 @@ struct vdpasim_virtqueue {
>>>> #define VDPASIM_NET_FEATURES    (VDPASIM_FEATURES | \
>>>>                  (1ULL << VIRTIO_NET_F_MAC))
>>>>+struct vdpasim;
>>>>+
>>>> struct vdpasim_dev_attr {
>>>>     u64 supported_features;
>>>>     size_t config_size;
>>>>@@ -65,6 +67,7 @@ struct vdpasim_dev_attr {
>>>>     u32 id;
>>>>     work_func_t work_fn;
>>>>+    void (*get_config)(struct vdpasim *vdpasim, void *config);
>>>> };
>>>> /* State of each vdpasim device */
>>>>@@ -520,8 +523,6 @@ static u64 vdpasim_get_features(struct 
>>>>vdpa_device *vdpa)
>>>> static int vdpasim_set_features(struct vdpa_device *vdpa, u64 
>>>>features)
>>>> {
>>>>     struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>>>>-    struct virtio_net_config *config =
>>>>-        (struct virtio_net_config *)vdpasim->config;
>>>>     /* DMA mapping must be done by driver */
>>>>     if (!(features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)))
>>>>@@ -529,15 +530,6 @@ static int vdpasim_set_features(struct 
>>>>vdpa_device *vdpa, u64 features)
>>>>     vdpasim->features = features & 
>>>>vdpasim->dev_attr.supported_features;
>>>>-    /* We generally only know whether guest is using the legacy 
>>>>interface
>>>>-     * here, so generally that's the earliest we can set config 
>>>>fields.
>>>>-     * Note: We actually require VIRTIO_F_ACCESS_PLATFORM above which
>>>>-     * implies VIRTIO_F_VERSION_1, but let's not try to be 
>>>>clever here.
>>>>-     */
>>>>-
>>>>-    config->mtu = cpu_to_vdpasim16(vdpasim, 1500);
>>>>-    config->status = cpu_to_vdpasim16(vdpasim, VIRTIO_NET_S_LINK_UP);
>>>>-    memcpy(config->mac, macaddr_buf, ETH_ALEN);
>>>>     return 0;
>>>> }
>>>>@@ -593,8 +585,12 @@ static void vdpasim_get_config(struct 
>>>>vdpa_device *vdpa, unsigned int offset,
>>>> {
>>>>     struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>>>>-    if (offset + len < vdpasim->dev_attr.config_size)
>>>>-        memcpy(buf, vdpasim->config + offset, len);
>>>>+    if (offset + len > vdpasim->dev_attr.config_size)
>>>>+        return;
>>>>+
>>>>+    vdpasim->dev_attr.get_config(vdpasim, vdpasim->config);
>>>>+
>>>>+    memcpy(buf, vdpasim->config + offset, len);
>>>> }
>>>
>>>
>>>I wonder how much value we can get from vdpasim->config consider 
>>>we've already had get_config() method.
>>>
>>>Is it possible to copy to the buffer directly here?
>>
>>I had thought of eliminating it too, but then I wanted to do something 
>>similar to what we do in QEMU (hw/virtio/virtio.c), leaving in the 
>>simulator core the buffer, the memory copy (handling offset and len), 
>>and the boundary checks.
>>
>>In this way each device should simply fill the entire configuration 
>>and we can avoid code duplication.
>>
>>Storing the configuration in the core may also be useful if some 
>>device needs to support config writes.
>
>
>I think in that way we need should provide config_write().

Yes, I'll add set_config() callback.

>
>
>>
>>Do you think it makes sense, or is it better to move everything in the 
>>device?
>
>
>I prefer to do that in the device but it's also fine keep what the 
>patch has done.

Okay, for now I'll keep it and add the set_config() callback, but I'm 
open to move it in the device.

Thanks,
Stefano