On Mon, Oct 13, 2025 at 06:29:44PM +0200, Francesco Valla wrote: > Hello Matias, > > On Monday, 13 October 2025 at 11:52:49 Matias Ezequiel Vara Larsen > <[email protected]> wrote: > > On Fri, Oct 10, 2025 at 11:20:22PM +0200, Francesco Valla wrote: > > > On Friday, 10 October 2025 at 17:46:25 Matias Ezequiel Vara Larsen > > > <[email protected]> wrote: > > > > On Thu, Sep 11, 2025 at 10:59:40PM +0200, Francesco Valla wrote: > > > > > Hello Mikhail, Harald, > > > > > > > > > > hoping there will be a v6 of this patch soon, a few comments: > > > > > > > > > > > > > I am working on the v6 by addressing the comments in this thread. > > > > > > > > > On Monday, 8 January 2024 at 14:10:35 Mikhail Golubev-Ciuchea > > > > > <[email protected]> wrote: > > > > > > > > > > [...] > > > > > > > > > > > + > > > > > > +/* virtio_can private data structure */ > > > > > > +struct virtio_can_priv { > > > > > > + struct can_priv can; /* must be the first member */ > > > > > > + /* NAPI for RX messages */ > > > > > > + struct napi_struct napi; > > > > > > + /* NAPI for TX messages */ > > > > > > + struct napi_struct napi_tx; > > > > > > + /* The network device we're associated with */ > > > > > > + struct net_device *dev; > > > > > > + /* The virtio device we're associated with */ > > > > > > + struct virtio_device *vdev; > > > > > > + /* The virtqueues */ > > > > > > + struct virtqueue *vqs[VIRTIO_CAN_QUEUE_COUNT]; > > > > > > + /* I/O callback function pointers for the virtqueues */ > > > > > > + vq_callback_t *io_callbacks[VIRTIO_CAN_QUEUE_COUNT]; > > > > > > + /* Lock for TX operations */ > > > > > > + spinlock_t tx_lock; > > > > > > + /* Control queue lock. Defensive programming, may be not needed > > > > > > */ > > > > > > + struct mutex ctrl_lock; > > > > > > + /* Wait for control queue processing without polling */ > > > > > > + struct completion ctrl_done; > > > > > > + /* List of virtio CAN TX message */ > > > > > > + struct list_head tx_list; > > > > > > + /* Array of receive queue messages */ > > > > > > + struct virtio_can_rx rpkt[128]; > > > > > > > > > > This array should probably be allocated dynamically at probe - maybe > > > > > using a module parameter instead of a hardcoded value as length? > > > > > > > > > > > > > If I allocate this array in probe(), I would not know sdu[] in advance > > > > if I defined it as a flexible array. That made me wonder: can sdu[] be > > > > defined as flexible array for rx? > > > > > > > > Thanks. > > > > > > > > > > One thing that can be done is to define struct virtio_can_rx as: > > > > > > struct virtio_can_rx { > > > #define VIRTIO_CAN_RX 0x0101 > > > __le16 msg_type; > > > __le16 length; /* 0..8 CC, 0..64 CAN-FD, 0..2048 CAN-XL, 12 bits */ > > > __u8 reserved_classic_dlc; /* If CAN classic length = 8 then DLC can be > > > 8..15 */ > > > __u8 padding; > > > __le16 reserved_xl_priority; /* May be needed for CAN XL priority */ > > > __le32 flags; > > > __le32 can_id; > > > __u8 sdu[] __counted_by(length); > > > }; > > > > > > and then allocate the rpkt[] array using the maximum length for SDU: > > > > > > priv->rpkt = kcalloc(num_rx_buffers, > > > sizeof(struct virtio_can_rx) + VIRTIO_CAN_MAX_DLEN, > > > GFP_KERNEL); > > > > > > In this way, the size of each member of rpkt[] is known and is thus > > > suitable for virtio_can_populate_vqs(). > > > > > > > > > > Thanks for your answer. What is the value of VIRTIO_CAN_MAX_DLEN? I > > can't find it nor in the code or in the spec. I guess is 64 bytes? Also, > > IIUC, using __counted_by() would not end up saving space but adding an > > extra check for the compiler. Am I right? In that case, can't I just use > > a fixed array of VIRTIO_CAN_MAX_DLEN bytes? > > My bad, I forgot to say that VIRTIO_CAN_MAX_DLEN has to be defined, but: > given some more thoughts, maybe this can be a dynamic value based on > the features received from the virtio framework, to avoid wasting memory? > > E.g.: > > if (virtio_has_feature(VIRTIO_CAN_F_CAN_FD)) > sdu_len = CANFD_MAX_DLEN; > else > sdu_len = CAN_MAX_DLEN; > > priv->rpkt = kcalloc(num_rx_buffers, sizeof(struct virtio_can_rx) + sdu_len, > GFP_KERNEL); > > > My understanding of __counted_by() is the same: additional checks but nothing > more. > > > CAN-XL appears to be not supported by the virtio specs v1.4 [1], but if/when > it will be, the addition of an additional case would be simple. > > [1] > https://github.com/oasis-tcs/virtio-spec/blob/virtio-1.4/device-types/can/description.tex#L33 >
Sounds good, I'll add that. Matias
