const char *buf, /* The buffer with input */
size_t length, /* The buffer's length */
loff_t *offset) /* offset to file - ignore */
#else
static int module_input(
struct inode *inode, /* The file's inode */
struct file *file, /* The file itself */
const char *buf, /* The buffer with the input */
int length) /* The buffer's length */
#endif
{
int i;
/* Put the input into Message, where module_output
* 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] = '\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;