Re: RTDM Kernel Driver exchanging with Linux Application via /dev/rtp0/ using RTIPC Protocol and XDDP socket

[ayaida marwane <ayaida_marwane@yahoo.fr>]

> Le 5 mai 2020 à 21:22, Jan Kiszka <jan.kiszka@siemens.com> a écrit :
> 
> On 29.04.20 23:21, ayaida marwane via Xenomai wrote:
>> Dear all,
>> I am trying to develop a simple example of a RTDM driver running from Xenomai Kernel, that exchanges a string ("Hello world!") with a Linux Application using /dev/rtp0.
>> I already succeeded doing this with Xenomai 2 using RT_PIPE. However, as I understand, this using RT_PIPE from the Kernel depreciated in Xenomai 3 and it is recommended to use RTIPC Protocol and a XDDP socket.
>> In the documentation, there are some examples (xddp-echo.c, xddp-label.c and xddp-stream.c), that worked well in my Xenomai 3.0.7 installed on a Raspberry Pi3.
>> However, these examples are using a simple socket Protocol (socket(), bind(), sendto() and recvfrom()) using the POSIX Skin. So, using this in a RTDM module, will surely not work.
>> Therefore, as I understand, I have to use the Real-time IPC defined in the RTDM Skin  (socket__AF_RTIPC(), bind__AF_RTIPC(), sendmsg__AF_RTIPC() and recvmsg__AF_RTIPC()).
> 
> These calls do not exist (where did you find them?) as your build error also says. Check the inter-driver API for such a stacking scenario. It provides rtdm_socket, rtdm_sendmsg etc.
> 
> Depending on what kind of Linux application shall use the API in the end, it can be simpler to compile that for Xenomai and use the RTDM userspace API directly to talk to the RTDM driver.
> 
> Jan
> 
> -- 
> Siemens AG, Corporate Technology, CT RDA IOT SES-DE
> Corporate Competence Center Embedded Linux

Dear Jan,

Thank you for your replay. I tried to use the inter-driver API to communicate between the RTDM driver and the Linux side using /dev/rtp0. The exemple is given below (inspired from xddp-echo.c):

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#include <rtdm/driver.h>
#include <rtdm/ipc.h>

#define XDDP_PORT 0     /* [0..CONFIG-XENO_OPT_PIPE_NRDEV - 1] and /dev/rtpX  */

static const char *msg = "Hello world!";

static int __init my_module_init (void)
{
    struct sockaddr_ipc saddr;
    int ret, s, len;
    size_t poolsz;
    char buf[128];

    rtdm_printk(KERN_INFO "%s.%s()\n", THIS_MODULE->name, __FUNCTION__);

    s = rtdm_socket(AF_RTIPC, SOCK_DGRAM, IPCPROTO_XDDP);
    if (s < 0) {
        rtdm_printk(KERN_INFO "socket error\n");
    }

    poolsz = 16384; /* bytes */
    ret = rtdm_setsockopt(s, SOL_XDDP, XDDP_POOLSZ,
             &poolsz, sizeof(poolsz));
    if (ret)
        rtdm_printk(KERN_INFO "setsockopt error\n");

    memset(&saddr, 0, sizeof(saddr));
    saddr.sipc_family = AF_RTIPC;
    saddr.sipc_port = XDDP_PORT;
    ret = rtdm_bind(s, (struct sockaddr *)&saddr, sizeof(saddr));
    if (ret)
        rtdm_printk(KERN_INFO "bind error\n");

    len = strlen(msg);

    rtdm_printk(KERN_INFO "%s: sent %d bytes, \"%.*s\"\n",  __FUNCTION__, len, len, msg);

    ret = rtdm_sendto(s, msg, len, 0, NULL, 0);

    if (ret != len)
        rtdm_printk(KERN_INFO "sendto error = %d \n", ret);

    ret = rtdm_recvfrom(s, buf, sizeof(buf), 0, NULL, 0);
    if (ret <= 0)
        rtdm_printk(KERN_INFO "recvfrom error\n");

    rtdm_printk(KERN_INFO "%s: ==> Received from Linux %d bytes : %.*s\n", __FUNCTION__, ret, ret, buf);

	return 0;
}

static void __exit my_module_exit (void)
{
	rtdm_printk(KERN_INFO "%s.%s()\n", THIS_MODULE->name, __FUNCTION__);
}
module_init(my_module_init);
module_exit(my_module_exit);
MODULE_LICENSE("GPL");

—————————————————————————————————————————————— 

Now, the RTDM driver compiles. However, the problem is that when I execute it, it gives:

—————————————————————————————————————————————— 

[ 5939.538234] rtdm_xddp.my_module_init()
[ 5939.538437] my_module_init: sent 12 bytes, "Hello world!"
[ 5939.538451] sendto error = -38 
[ 5939.538458] recvfrom error
[ 5939.538468] my_module_init: ==> Received from Linux -38 bytes : 
[ 5944.279224] rtdm_xddp.my_module_exit()

—————————————————————————————————————————————— 

The sendto fails. When I see the signification of this error is:

—————————————————————————————————————————————— 

/*
 * This error code is special: arch syscall entry code will return
 * -ENOSYS if users try to call a syscall that doesn't exist.  To keep
 * failures of syscalls that really do exist distinguishable from
 * failures due to attempts to use a nonexistent syscall, syscall
 * implementations should refrain from returning -ENOSYS.
 */
#define ENOSYS          38      /* Invalid system call number */

—————————————————————————————————————————————— 

Why it does not work? I found that the parameters of sendto() and rtdm_sendto() are the same.

Thanks for your help.

BR,
Marwane.