如何在内核编程中执行shell命令？

Question

I want to use system() function of stdlib.h in my c code. I am actually working on kernel programming.

Whenever i want to use system() in it, it gives error to stdlib.h saying no such file found.

Answer 1

It's simple!

#include <linux/kmod.h>

char * envp[] = { "HOME=/", NULL };
char * argv[] = { "/bin/ls", NULL };

call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);

Answer 2

What you probably want is executing a userspace function . That SE answer includes a link to an IBM article with an example userspace process invoked from the kernel. The search terms you should use are "usermodehelper" and "usermode helper".

In the kernel, see:

yba@tavas:~/linux-2.6/linux-2.6$ find . -type f | xargs grep "usermode.helper"
./kernel/cgroup.c:      /* Drop the lock while we invoke the usermode helper,
./kernel/kmod.c:    /* CLONE_VFORK: wait until the usermode helper has execve'd
./kernel/kmod.c: * call_usermodehelper_setup - prepare to call a usermode helper
./drivers/block/drbd/drbd_int.h:extern char usermode_helper[];
./drivers/block/drbd/drbd_nl.c: char *argv[] = {usermode_helper, cmd, mb, NULL };
./drivers/block/drbd/drbd_nl.c: dev_info(DEV, "helper command: %s %s %s\n", usermode_helper, cmd, mb);
./drivers/block/drbd/drbd_nl.c: ret = call_usermodehelper(usermode_helper, argv, envp, UMH_WAIT_PROC);
./drivers/block/drbd/drbd_nl.c:             usermode_helper, cmd, mb,
./drivers/block/drbd/drbd_nl.c:             usermode_helper, cmd, mb,
./drivers/block/drbd/drbd_nl.c: char *argv[] = {usermode_helper, cmd, tconn->name, NULL };
./drivers/block/drbd/drbd_nl.c: conn_info(tconn, "helper command: %s %s %s\n", usermode_helper, cmd, tconn->name);
./drivers/block/drbd/drbd_nl.c: ret = call_usermodehelper(usermode_helper, argv, envp, UMH_WAIT_PROC);
./drivers/block/drbd/drbd_nl.c:           usermode_helper, cmd, tconn->name,
./drivers/block/drbd/drbd_nl.c:           usermode_helper, cmd, tconn->name,
./drivers/block/drbd/drbd_main.c:char usermode_helper[80] = "/sbin/drbdadm";
./drivers/block/drbd/drbd_main.c:module_param_string(usermode_helper, usermode_helper, sizeof(usermode_helper), 0644);
./drivers/block/drbd/drbd_main.c:        * currently blocked waiting for that usermode helper to
./security/keys/request_key.c: * Initialise a usermode helper that is going to have a specific session
./security/keys/request_key.c: * Clean up a usermode helper with session keyring.
./security/keys/request_key.c: * Call a usermode helper with a specific session keyring.

Answer 3

No easy way, because system() is a user-level C library function, which involve many system calls, including:

 sys_fork()
 sys_execve()

You could acchive system() effect using the following ways ( I guess):

 create a kernel thread.

 let the kernel thread execute sys_execve( your command name)

Not sure this could work, but you can try.

Answer 4

You can't use system() from the kernel. End of story. There is no application level code to execute from the kernel space.