Ори Померанц - Энциклопедия разработчика модулей ядра Linux

* will later be able to use it */

for(i=0; 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] = '\0';

/* 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