On Sun, Aug 9, 2020 at 2:13 AM Willem de Bruijn
<willemdebruijn.ker...@gmail.com> wrote:
>
> The patch is analogous to commit c7ca03c216ac
> ("drivers/net/wan/lapbether: Added needed_headroom and a skb->len
> check").
>
> Seems to make sense based on call stack
>
> x25_asy_xmit // skb_pull(skb, 1)
> lapb_data_request
> lapb_kick
> lapb_send_iframe // skb_push(skb, 2)
> lapb_transmit_buffer // skb_push(skb, 1)
> lapb_data_transmit
> x25_asy_data_transmit
> x25_asy_encaps
Thank you!
> But I frankly don't know this code and would not modify logic that no
> one has complained about for many years without evidence of a real
> bug.
Maybe it's better to submit this patch to "net-next"? I want to do
this change because:
1) I hope to set needed_headroom properly for all three X.25 drivers
(lapbether, x25_asy, hdlc_x25) in the kernel. So that the upper layer
(net/x25) can be changed to use needed_headroom to allocate skb,
instead of the current way of using a constant to estimate the needed
headroom.
2) The code quality of this driver is actually very low, and I also
hope to improve it gradually. Actually this driver had been completely
broken for many years and no one had noticed this until I fixed it in
commit 8fdcabeac398 (drivers/net/wan/x25_asy: Fix to make it work)
last month. This driver has a lot of other issues and I wish I can
gradually fix them, too.
> Were you able to actually exercise this path, similar to lapb_ether:
> configure the device, send data from a packet socket? If so, can you
> share the configuration steps?
Yes, I can run this driver. The driver is a software driver that runs
over TTY links. We can set up a x25_asy link over a virtual TTY link
using this method:
First:
sudo modprobe lapb
sudo modprobe x25_asy
Then set up a virtual TTY link:
socat -d -d pty,cfmakeraw pty,cfmakeraw &
This will open a pair of PTY ports.
(The "socat" program can be installed from package managers.)
Then use a C program to set the line discipline for the two PTY ports:
Simplified version for reading:
int ldisc = N_X25;
int fd = open("path/to/pty", O_RDWR);
ioctl(fd, TIOCSETD, &ldisc);
close(fd);
Complete version for running:
https://github.com/hyanggi/testing_linux/blob/master/network_x25/lapb/set_ldisc.c
Then we'll get two network interfaces named x25asy0 and x25asy1.
Then we do:
sudo ip link set x25asyN up
to bring them up.
After we set up this x25_asy link, we can test it using AF_PACKET sockets:
In the connected-side C program:
Complete version for running:
https://github.com/hyanggi/testing_linux/blob/master/network_x25/lapb/receiver.c
Simplified version for reading:
int sockfd = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_ALL));
/* Get interface index */
struct ifreq ifr;
strcpy(ifr.ifr_name, "interface_name");
ioctl(sockfd, SIOCGIFINDEX, &ifr);
int ifindex = ifr.ifr_ifindex;
struct sockaddr_ll sender_addr;
socklen_t sender_addr_len = sizeof sender_addr;
char buffer[1500];
while (1) {
ssize_t length = recvfrom(sockfd, buffer, sizeof buffer, 0,
(struct sockaddr *)&sender_addr,
&sender_addr_len);
if (sender_addr.sll_ifindex != ifindex)
continue;
else if (buffer[0] == 0)
printf("Data received.\n");
else if (buffer[0] == 1)
printf("Connected by the other side.\n");
else if (buffer[0] == 2) {
printf("Disconnected by the other side.\n");
break;
}
}
close(sockfd);
In the connecting-side C program:
Complete version for running:
https://github.com/hyanggi/testing_linux/blob/master/network_x25/lapb/sender.c
Simplified version for reading:
int sockfd = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_ALL));
/* Get interface index */
struct ifreq ifr;
strcpy(ifr.ifr_name, "interface_name");
ioctl(sockfd, SIOCGIFINDEX, &ifr);
int ifindex = ifr.ifr_ifindex;
struct sockaddr_ll addr = {
.sll_family = AF_PACKET,
.sll_ifindex = ifindex,
};
/* Connect */
sendto(sockfd, "\x01", 1, 0, (struct sockaddr *)&addr, sizeof addr);
/* Send data */
sendto(sockfd, "\x00" "data", 5, 0, (struct sockaddr *)&addr,
sizeof addr);
sleep(1); /* Wait a while before disconnecting */
/* Disconnect */
sendto(sockfd, "\x02", 1, 0, (struct sockaddr *)&addr, sizeof addr);
close(sockfd);
I'm happy to answer any questions. Thank you so much!
