On 2/4/22 11:08 AM, Lorenzo Bianconi wrote:
[...]
In kernel, the nr_frags checking is against MAX_SKB_FRAGS,
but if /proc/sys/net/core/max_skb_flags is 2 or more less
than MAX_SKB_FRAGS, the test won't fail, right?
yes, you are right. Should we use the same definition used in
include/linux/skbuff.h instead? Something like:
if (65536 / page_size + 1 < 16)
max_skb_flags = 16;
else
max_skb_flags = 65536/page_size + 1;
The maximum packet size limit 64KB won't change anytime soon.
So the above should work. Some comments to explain why using
the above formula will be good.
ack, I will do in v2.
I can see there is a on-going discussion here [0] about increasing
MAX_SKB_FRAGS. I guess we can put on-hold this patch and see how
MAX_SKB_FRAGS will be changed.
Thanks for the link. The new patch is going to increase
MAX_SKB_FRAGS and it is possible that will be changed again
(maybe under some config options).
The default value for
/proc/sys/net/core/max_skb_flags is MAX_SKB_FRAGS and I suspect
anybody is bothering to change it. So your patch is okay to me.
Maybe change a little bit -ENOMEM error message. current,
ASSERT_EQ(err, -ENOMEM, "unsupported buffer size");
to
ASSERT_EQ(err, -ENOMEM, "unsupported buffer size, possible
non-default /proc/sys/net/core/max_skb_flags?");
Regards,
Lorenzo
[0] https://lore.kernel.org/all/202202031315.B425Ipe8-lkp@xxxxxxxxx/t/#ma1b2c7e71fe9bc69e24642a62dadf32fda7d5f03
Regards,
Lorenzo
Regards,
Lorenzo
+
+ num = fscanf(f, "%d", &max_skb_frags);
+ fclose(f);
+
+ if (!ASSERT_EQ(num, 1, "max_skb_frags read failed"))
+ goto out;
+
+ /* xdp_buff linear area size is always set to 4096 in the
+ * bpf_prog_test_run_xdp routine.
+ */
+ buf_size = 4096 + (max_skb_frags + 1) * sysconf(_SC_PAGE_SIZE);
+ buf = malloc(buf_size);
+ if (!ASSERT_OK_PTR(buf, "alloc buf"))
+ goto out;
+
+ memset(buf, 0, buf_size);
+ offset = (__u32 *)buf;
+ *offset = 16;
+ buf[*offset] = 0xaa;
+ buf[*offset + 15] = 0xaa;
+
+ topts.data_in = buf;
+ topts.data_out = buf;
+ topts.data_size_in = buf_size;
+ topts.data_size_out = buf_size;
+
+ err = bpf_prog_test_run_opts(prog_fd, &topts);
+ ASSERT_EQ(err, -ENOMEM, "unsupported buffer size");
+ free(buf);
out:
bpf_object__close(obj);
}
