Читать интересную книгу Энциклопедия разработчика модулей ядра Linux - Ори Померанц

 * will later be able to use it */

 for(i=0; i<MESSAGE_LENGTH-1 && i<length; i++)

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)

 get_user(Message[i], buf+i);

#else

 Message[i] = get_user(buf+i);

#endif

 /* we want a standard, zero terminated string */

 Message[i] = '';

 /* We need to return the number of input characters used */

 return i;

}

/* 1 if the file is currently open by somebody */

int Already_Open = 0;

 /* Queue of processes who want our file */

static struct wait_queue *WaitQ = NULL;

/* Called when the /proc file is opened */

static int module_open(struct inode *inode, struct file *file) {

 /* If the file's flags include O_NONBLOCK, it means

 * the process doesn't want to wait for the file.

 * In this case, if the file is already open, we

 * should fail with -EAGAIN, meaning "you'll have to

 * try again", instead of blocking a process which

 * would rather stay awake. */

 if ((file->f_flags & O_NONBLOCK) && Already_Open) return -EAGAIN;

 /* This is the correct place for MOD_INC_USE_COUNT

 * because if a process is in the loop, which is

 * within the kernel module, the kernel module must

 * not be removed. */

 MOD_INC_USE_COUNT;

 /* If the file is already open, wait until it isn't */

 while (Already_Open) {

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)

  int i, is_sig=0;

#endif

  /* This function puts the current process,

  * including any system calls, such as us, to sleep.

  * Execution will be resumed right after the function

  * call, either because somebody called

  * wake_up(&WaitQ) (only module_close does that,

  * when the file is closed) or when a signal, such

  * as Ctrl-C, is sent to the process */

  module_interruptible_sleep_on(&WaitQ);

  /* If we woke up because we got a signal we're not

  * blocking, return -EINTR (fail the system call).

  * This allows processes to be killed or stopped. */

  /*

  * Emmanuel Papirakis:

  *

  * This is a little update to work with 2.2.*. Signals

  * now are contained in two words (64 bits) and are

  * stored in a structure that contains an array of two

  * unsigned longs. We now have to make 2 checks in our if.

  *

  * Ori Pomerantz:

  *

  * Nobody promised me they'll never use more than 64

  * bits, or that this book won't be used for a version

  * of Linux with a word size of 16 bits. This code

  * would work in any case. */

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)

  for(i=0; i<_NSIG_WORDS && !is_sig; i++) is_sig = current->signal.sig[i] & current->blocked.sig[i];

  if (is_sig) {

#else

  if (current->signal & current->blocked) {

#endif

   /* It's important to put MOD_DEC_USE_COUNT here,

   * because for processes where the open is

   * interrupted there will never be a corresponding

   * close. If we don't decrement the usage count

   * here, we will be left with a positive usage

   * count which we'll have no way to bring down to

   * zero, giving us an immortal module, which can

   * only be killed by rebooting the machine. */

   MOD_DEC_USE_COUNT;

   return -EINTR;

  }

 }

 /* If we got here, Already_Open must be zero */

 /* Open the file */

 Already_Open = 1;

 return 0;  /* Allow the access */

}

/* Called when the /proc file is closed */

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)

int module_close(struct inode *inode, struct file *file)

#else

void module_close(struct inode *inode, struct file *file)

#endif

{

 /* Set Already_Open to zero, so one of the processes

 * in the WaitQ will be able to set Already_Open back

 * to one and to open the file. All the other processes

 * will be called when Already_Open is back to one, so

 * they'll go back to sleep. */

 Already_Open = 0;

 /* Wake up all the processes in WaitQ, so if anybody

 * is waiting for the file, they can have it. */

 module_wake_up(&WaitQ);

 MOD_DEC_USE_COUNT;

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)

 return 0; /* success */

#endif

}

/* This function decides whether to allow an operation

* (return zero) or not allow it (return a non-zero

* which indicates why it is not allowed).

*

* The operation can be one of the following values:

* 0 - Execute (run the "file" - meaningless in our case)

* 2 - Write (input to the kernel module)

* 4 - Read (output from the kernel module)

*

* This is the real function that checks file

* permissions. The permissions returned by ls -l are

* for referece only, and can be overridden here. */

static int module_permission(struct inode *inode, int op) {

 /* We allow everybody to read from our module, but

 * only root (uid 0) may write to it */

 if (op == 4 || (op == 2 && current->euid == 0)) return 0;

 /* If it's anything else, access is denied */

 return -EACCES;

}

/* Structures to register as the /proc file, with

* pointers to all the relevant functions. *********** */

/* File operations for our proc file. This is where

* we place pointers to all the functions called when

* somebody tries to do something to our file. NULL

* means we don't want to deal with something. */

static struct file_operations File_Ops_4_Our_Proc_File = {

 NULL, /* lseek */

 module_output, /* "read" from the file */

 module_input, /* "write" to the file */

 NULL, /* readdir */

 NULL, /* select */

 NULL, /* ioctl */

 NULL, /* mmap */

 module_open,/* called when the /proc file is opened */

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)

 NULL, /* flush */

#endif

 module_close /* called when it's classed */

};

/* Inode operations for our proc file. We need it so

* we'll have somewhere to specify the file operations

* structure we want to use, and the function we use for

* permissions. It's also possible to specify functions

* to be called for anything else which could be done to an

* inode (although we don't bother, we just put NULL). */

static struct inode_operations Inode_Ops_4_Our_Proc_File = {

 &File_Ops_4_Our_Proc_File,

 NULL, /* create */

 NULL, /* lookup */

 NULL, /* link */

 NULL, /* unlink */

 NULL, /* symlink */

 NULL, /* mkdir */

 NULL, /* rmdir */

 NULL, /* mknod */

 NULL, /* rename */

 NULL, /* readlink */

 NULL, /* follow_link */

 NULL, /* readpage */

 NULL, /* writepage */

 NULL, /* bmap */

 NULL, /* truncate */

 module_permission /* check for permissions */

};

/* Directory entry */

static struct proc_dir_entry Our_Proc_File = {

 0, /* Inode number - ignore, it will be filled by proc_register[_dynamic] */

 5, /* Length of the file name */

 "sleep", /* The file name */

 S_IFREG | S_IRUGO | S_IWUSR,

  /* File mode - this is a regular file which

  * can be read by its owner, its group, and everybody

  * else. Also, its owner can write to it.

  *

  * Actually, this field is just for reference, it's

  * module_permission that does the actual check. It

  * could use this field, but in our implementation it

  * doesn't, for simplicity. */

 1, /* Number of links (directories where the file is referenced) */

 0, 0, /* The uid and gid for the file - we give it to root */

 80, /* The size of the file reported by ls. */

 &Inode_Ops_4_Our_Proc_File,

  /* A pointer to the inode structure for

  * the file, if we need it. In our case we

  * do, because we need a write function. */

 NULL

  /* The read function for the file.

  * Irrelevant, because we put it

  * in the inode structure above */

};

 /* Module initialization and cleanup **************** */

/* Initialize the module - register the proc file */

int init_module() {

 /* Success if proc_register_dynamic is a success,

 * failure otherwise */

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)

 return proc_register(&proc_root, &Our_Proc_File);

#else

 return proc_register_dynamic(&proc_root, &Our_Proc_File);

#endif

 /* proc_root is the root directory for the proc

 * fs (/proc). This is where we want our file to be

 * located. */

}

/* Cleanup - unregister our file from /proc. This could

* get dangerous if there are still processes waiting in

* WaitQ, because they are inside our open function,

* which will get unloaded. I'll explain how to avoid

* removal of a kernel module in such a case in chapter 10. */

void cleanup_module() {

 proc_unregister(&proc_root, Our_Proc_File.low_ino);

}

Замена для printk

В начале (глава1), я сказал, что X и программирование модулей ядра не совместимы. Это истинно при разработке модуля, но в фактическом использовании, Вы должны быть способны послать сообщениям любому tty[10]. Это важно для идентификации ошибок после того, как модуль выпущен, потому что он будет использоваться через любой из терминалов.

Путем этого достичь: используя текущий указатель на задачу, выполняемую в настоящее время, получить ее структуру tty. Затем мы смотрим внутри этой структура tty, чтобы найти указатель на функцию, пишущую строку на tty. Ее мы и используем для вывода.

printk.c

/* printk.c - send textual output to the tty you're

* running on, regardless of whether it's passed

* through X11, telnet, etc.

*/

/* Copyright (C) 1998 by Ori Pomerantz */

/* The necessary header files */

/* Standard in kernel modules */

#include <linux/kernel.h> /* We're doing kernel work */

#include <linux/module.h> /* Specifically, a module */

/* Deal with CONFIG_MODVERSIONS */

#if CONFIG_MODVERSIONS==1

#define MODVERSIONS

#include <linux/modversions.h>

#endif

/* Necessary here */

#include <linux/sched.h> /* For current */

#include <linux/tty.h> /* For the tty declarations */