On 22.07.2022 12:20:43, Vincent Mailhol wrote:
> I do not buy your argument that you can not do sizeof(struct
> canxl_frame) because of naming.
>
> With a flexible array member, I can do:
>
> struct canxl_frame {
> canid_t prio; /* 11 bit priority for arbitration (canid_t) */
> __u8 flags; /* additional flags for CAN XL */
> __u8 sdt; /* SDU (service data unit) type */
> __u16 len; /* frame payload length in byte */
> __u32 af; /* acceptance field */
> __u8 data[];
> };
>
> void foo (int s)
> {
> struct canxl_frame cxl_hdr = { 0 };
> struct canxl_frame *cxl1, *cxl2;
> size_t cxl2_data_len, cxl2_frame_len;
>
> /* read header */
> assert(read(s, &cxl_hdr, sizeof(cxl_hdr)) == sizeof(cxl_hdr));
> cxl1 = malloc(sizeof(*cxl1) + cxl_hdr.len);
> memcpy(cxl1, &cxl_hdr, sizeof(cxl_hdr));
> /* read remaining data */
> assert(read(s, cxl1->data, cxl1->len) == cxl1->len);
For performance reasons you probable don't want to split the read of a
single CAN frame over 2 read() syscalls. Also the CAN_RAW doesn't
support "split"-read now, but could be extended.
Marc
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