Mailing Lists: Apple Mailing Lists
 Image of Mac OS face in stamp
Userspace program cannot get data from ctl_enqueudata()
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Userspace program cannot get data from ctl_enqueudata()

Hello,

I am writing a small kext that sends data out to userspace via kernel
control. However, the userspace program cannot receive the expected
data. Anybody plese tell me what I did wrong?

My code is very simple: it sends a variable length text to userspace.
Todo that, I have a structure named MyLog, like below:
--
struct MyLog {
   int length; /* text length */
   uid_t uid;  /* uid that generated this action */
   unsigned int action; /* in kernel space: kauth_action_t action */
};
--

Then the ctrl_connect() method of kernel control is defined so
whenever a userspace program connect to kernel control, ctl_connect()
sends out few text. Please see below:

--
static int ctl_connect(kern_ctl_ref ctl_ref, struct sockaddr_ctl *sac,
void **unitinfo)
{
    struct MyLog log;
    char *text = "Greeting from kernelspace!";

    log.uid = 2006;
    log.action = 1010;
    log.length = strlen(text);

    /* put log information into queue */
    ctl_enqueuedata(ctl_ref, sac->sc_unit, &log, sizeof(log), 0);

    /* then put the variable text into queue */
    ctl_enqueuedata(ctl_ref, sac->sc_unit, text, strlen(text), 0);

    return 0;
}
--

My program in userspace connect to kernel, and trying to read data
out, like this:

---
       struct MyLog log;

       n = recv(gSocket, &log, sizeof(log), MSG_WAITALL);
       if (n == -1) {
           printf("Failed on getting data from kernel\n");
           return -1;
       }

       printf("Got packet of %d byte, variable length: %d\n", n, log.length);

       n = recv(gSocket, buffer, length, MSG_WAITALL);
       printf("Got exactly %d bytes\n", n);
       buffer[n] = '\0';

       printf("Action %d on %s (%d)\n", log.action, buffer, log.uid);

---

However, while I expect that my userspace program will get the text
"Greeting from kernelspace", it does not. In fact, I only got data
from the first recv() function, and my program printed out:

---
Got packet of 16 byte, variable length: 16
---

So far, it is correct. But then it hangs up there, instead of
succesfully execute the next recv()? Why that happens? In my kernel
code, I already put all the neccessary data in the control buffer, no?
(???)

Then I tried to copy another data into the kernel buffer (use another
command ctl_enqueudata() command). Then the userspace program quit the
hangup  status, and continue to print out data. But the data is not
what I expected, like below:
--
Got exactly 26 bytes
Action 1010 on  (2006)
--

As you can see, the text "Greeting from kernelspace" is no where to be
seen, although I got 26 bytes as I expected. The only problem is that
the data is incorrect.

It seems that the way I put the kernel data into the buffer is
incorrect, or what else should be fixed?


Thank you a lot, and have a nice weekend (I don't :-)
H
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Darwin-kernel mailing list      (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden





















Visit the Apple Store online or at retail locations.

1-800-MY-APPLE


Contact Apple | Terms of Use | Privacy Policy


Copyright © 2011 Apple Inc. All rights reserved.