mirror of https://github.com/tLDP/LDP
new
This commit is contained in:
gferg
parent
77ba6298b3
commit
47c55a069e
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/*
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* procfs1.c - create a "file" in /proc
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*
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*/
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#include <linux/module.h> /* Specifically, a module */
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#include <linux/kernel.h> /* We're doing kernel work */
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#include <linux/proc_fs.h> /* Necessary because we use the proc fs */
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#define procfs_name "helloworld"
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/**
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* This structure hold information about the /proc file
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*
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*/
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struct proc_dir_entry *Our_Proc_File;
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/* Put data into the proc fs file.
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*
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* Arguments
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* =========
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* 1. The buffer where the data is to be inserted, if
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* you decide to use it.
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* 2. A pointer to a pointer to characters. This is
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* useful if you don't want to use the buffer
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* allocated by the kernel.
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* 3. The current position in the file
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* 4. The size of the buffer in the first argument.
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* 5. Write a "1" here to indicate EOF.
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* 6. A pointer to data (useful in case one common
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* read for multiple /proc/... entries)
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*
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* Usage and Return Value
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* ======================
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* A return value of zero means you have no further
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* information at this time (end of file). A negative
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* return value is an error condition.
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*
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* For More Information
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* ====================
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* The way I discovered what to do with this function
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* wasn't by reading documentation, but by reading the
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* code which used it. I just looked to see what uses
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* the get_info field of proc_dir_entry struct (I used a
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* combination of find and grep, if you're interested),
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* and I saw that it is used in <kernel source
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* directory>/fs/proc/array.c.
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*
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* If something is unknown about the kernel, this is
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* usually the way to go. In Linux we have the great
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* advantage of having the kernel source code for
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* free - use it.
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*/
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int
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procfile_read(char *buffer,
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char **buffer_location,
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off_t offset, int buffer_length, int *eof, void *data)
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{
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int ret;
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printk(KERN_INFO "procfile_read (/proc/%s) called\n", procfs_name);
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/*
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* We give all of our information in one go, so if the
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* user asks us if we have more information the
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* answer should always be no.
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*
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* This is important because the standard read
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* function from the library would continue to issue
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* the read system call until the kernel replies
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* that it has no more information, or until its
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* buffer is filled.
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*/
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if (offset > 0) {
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/* we have finished to read, return 0 */
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ret = 0;
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} else {
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/* fill the buffer, return the buffer size */
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ret = sprintf(buffer, "HelloWorld!\n");
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}
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return ret;
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}
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int init_module()
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{
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Our_Proc_File = create_proc_entry(procfs_name, 0644, NULL);
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if (Our_Proc_File == NULL) {
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remove_proc_entry(procfs_name, &proc_root);
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printk(KERN_ALERT "Error: Could not initialize /proc/%s\n",
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procfs_name);
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return -ENOMEM;
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}
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Our_Proc_File->read_proc = procfile_read;
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Our_Proc_File->owner = THIS_MODULE;
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Our_Proc_File->mode = S_IFREG | S_IRUGO;
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Our_Proc_File->uid = 0;
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Our_Proc_File->gid = 0;
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Our_Proc_File->size = 37;
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printk(KERN_INFO "/proc/%s created\n", procfs_name);
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return 0; /* everything is ok */
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}
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void cleanup_module()
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{
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remove_proc_entry(procfs_name, &proc_root);
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printk(KERN_INFO "/proc/%s removed\n", procfs_name);
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}
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/**
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* procfs2.c - create a "file" in /proc
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*
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*/
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#include <linux/module.h> /* Specifically, a module */
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#include <linux/kernel.h> /* We're doing kernel work */
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#include <linux/proc_fs.h> /* Necessary because we use the proc fs */
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#include <asm/uaccess.h> /* for copy_from_user */
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#define PROCFS_MAX_SIZE 1024
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#define PROCFS_NAME "buffer1k"
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/**
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* This structure hold information about the /proc file
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*
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*/
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static struct proc_dir_entry *Our_Proc_File;
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/**
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* The buffer used to store character for this module
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*
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*/
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static char procfs_buffer[PROCFS_MAX_SIZE];
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/**
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* The size of the buffer
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*
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*/
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static unsigned long procfs_buffer_size = 0;
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/**
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* This function is called then the /proc file is read
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*
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*/
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int
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procfile_read(char *buffer,
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char **buffer_location,
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off_t offset, int buffer_length, int *eof, void *data)
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{
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int ret;
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printk(KERN_INFO "procfile_read (/proc/%s) called\n", PROCFS_NAME);
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if (offset > 0) {
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/* we have finished to read, return 0 */
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ret = 0;
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} else {
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/* fill the buffer, return the buffer size */
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memcpy(buffer, procfs_buffer, procfs_buffer_size);
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ret = procfs_buffer_size;
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}
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return ret;
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}
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/**
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* This function is called with the /proc file is written
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*
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*/
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int procfile_write(struct file *file, const char *buffer, unsigned long count,
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void *data)
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{
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/* get buffer size */
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procfs_buffer_size = count;
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if (procfs_buffer_size > PROCFS_MAX_SIZE ) {
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procfs_buffer_size = PROCFS_MAX_SIZE;
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}
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/* write data to the buffer */
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if ( copy_from_user(procfs_buffer, buffer, procfs_buffer_size) ) {
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return -EFAULT;
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}
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return procfs_buffer_size;
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}
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/**
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*This function is called when the module is loaded
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*
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*/
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int init_module()
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{
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/* create the /proc file */
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Our_Proc_File = create_proc_entry(PROCFS_NAME, 0644, NULL);
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if (Our_Proc_File == NULL) {
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remove_proc_entry(PROCFS_NAME, &proc_root);
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printk(KERN_ALERT "Error: Could not initialize /proc/%s\n",
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PROCFS_NAME);
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return -ENOMEM;
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}
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Our_Proc_File->read_proc = procfile_read;
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Our_Proc_File->write_proc = procfile_write;
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Our_Proc_File->owner = THIS_MODULE;
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Our_Proc_File->mode = S_IFREG | S_IRUGO;
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Our_Proc_File->uid = 0;
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Our_Proc_File->gid = 0;
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Our_Proc_File->size = 37;
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printk(KERN_INFO "/proc/%s created\n", PROCFS_NAME);
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return 0; /* everything is ok */
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}
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/**
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*This function is called when the module is unloaded
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*
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*/
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void cleanup_module()
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{
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remove_proc_entry(PROCFS_NAME, &proc_root);
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printk(KERN_INFO "/proc/%s removed\n", PROCFS_NAME);
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}
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/*
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* procfs3.c - create a "file" in /proc, use the file_operation way
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* to manage the file.
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*/
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#include <linux/kernel.h> /* We're doing kernel work */
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#include <linux/module.h> /* Specifically, a module */
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#include <linux/proc_fs.h> /* Necessary because we use proc fs */
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#include <asm/uaccess.h> /* for copy_*_user */
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#define PROC_ENTRY_FILENAME "buffer2k"
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#define PROCFS_MAX_SIZE 2048
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/**
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* The buffer (2k) for this module
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*
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*/
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static char procfs_buffer[PROCFS_MAX_SIZE];
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/**
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* The size of the data hold in the buffer
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*
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*/
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static unsigned long procfs_buffer_size = 0;
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/**
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* The structure keeping information about the /proc file
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*
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*/
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static struct proc_dir_entry *Our_Proc_File;
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/**
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* This funtion is called when the /proc file is read
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*
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*/
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static ssize_t procfs_read(struct file *filp, /* see include/linux/fs.h */
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char *buffer, /* buffer to fill with data */
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size_t length, /* length of the buffer */
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loff_t * offset)
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{
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static int finished = 0;
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/*
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* We return 0 to indicate end of file, that we have
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* no more information. Otherwise, processes will
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* continue to read from us in an endless loop.
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*/
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if ( finished ) {
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printk(KERN_INFO "procfs_read: END\n");
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finished = 0;
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return 0;
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}
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finished = 1;
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/*
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* We use put_to_user to copy the string from the kernel's
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* memory segment to the memory segment of the process
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* that called us. get_from_user, BTW, is
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* used for the reverse.
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*/
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if ( copy_to_user(buffer, procfs_buffer, procfs_buffer_size) ) {
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return -EFAULT;
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}
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printk(KERN_INFO "procfs_read: read %lu bytes\n", procfs_buffer_size);
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return procfs_buffer_size; /* Return the number of bytes "read" */
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}
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/*
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* This function is called when /proc is written
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*/
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static ssize_t
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procfs_write(struct file *file, const char *buffer, size_t len, loff_t * off)
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{
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if ( len > PROCFS_MAX_SIZE ) {
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procfs_buffer_size = PROCFS_MAX_SIZE;
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}
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else {
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procfs_buffer_size = len;
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}
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if ( copy_from_user(procfs_buffer, buffer, procfs_buffer_size) ) {
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return -EFAULT;
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}
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printk(KERN_INFO "procfs_write: write %lu bytes\n", procfs_buffer_size);
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return procfs_buffer_size;
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}
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/*
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* This function decides whether to allow an operation
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* (return zero) or not allow it (return a non-zero
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* which indicates why it is not allowed).
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*
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* The operation can be one of the following values:
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* 0 - Execute (run the "file" - meaningless in our case)
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* 2 - Write (input to the kernel module)
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* 4 - Read (output from the kernel module)
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*
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* This is the real function that checks file
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* permissions. The permissions returned by ls -l are
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* for referece only, and can be overridden here.
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*/
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static int module_permission(struct inode *inode, int op, struct nameidata *foo)
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{
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/*
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* We allow everybody to read from our module, but
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* only root (uid 0) may write to it
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*/
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if (op == 4 || (op == 2 && current->euid == 0))
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return 0;
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/*
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* If it's anything else, access is denied
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*/
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return -EACCES;
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}
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/*
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* The file is opened - we don't really care about
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* that, but it does mean we need to increment the
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* module's reference count.
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*/
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int procfs_open(struct inode *inode, struct file *file)
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{
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try_module_get(THIS_MODULE);
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return 0;
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}
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/*
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* The file is closed - again, interesting only because
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* of the reference count.
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*/
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int procfs_close(struct inode *inode, struct file *file)
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{
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module_put(THIS_MODULE);
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return 0; /* success */
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}
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static struct file_operations File_Ops_4_Our_Proc_File = {
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.read = procfs_read,
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.write = procfs_write,
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.open = procfs_open,
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.release = procfs_close,
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};
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/*
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* Inode operations for our proc file. We need it so
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* we'll have some place to specify the file operations
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* structure we want to use, and the function we use for
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* permissions. It's also possible to specify functions
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* to be called for anything else which could be done to
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* an inode (although we don't bother, we just put
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* NULL).
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*/
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static struct inode_operations Inode_Ops_4_Our_Proc_File = {
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.permission = module_permission, /* check for permissions */
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};
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/*
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* Module initialization and cleanup
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*/
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int init_module()
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{
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/* create the /proc file */
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Our_Proc_File = create_proc_entry(PROC_ENTRY_FILENAME, 0644, NULL);
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/* check if the /proc file was created successfuly */
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if (Our_Proc_File == NULL){
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printk(KERN_ALERT "Error: Could not initialize /proc/%s\n",
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PROC_ENTRY_FILENAME);
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return -ENOMEM;
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}
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Our_Proc_File->owner = THIS_MODULE;
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Our_Proc_File->proc_iops = &Inode_Ops_4_Our_Proc_File;
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Our_Proc_File->proc_fops = &File_Ops_4_Our_Proc_File;
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Our_Proc_File->mode = S_IFREG | S_IRUGO | S_IWUSR;
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Our_Proc_File->uid = 0;
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Our_Proc_File->gid = 0;
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Our_Proc_File->size = 80;
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printk(KERN_INFO "/proc/%s created\n", PROC_ENTRY_FILENAME);
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return 0; /* success */
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}
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void cleanup_module()
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{
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remove_proc_entry(PROC_ENTRY_FILENAME, &proc_root);
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printk(KERN_INFO "/proc/%s removed\n", PROC_ENTRY_FILENAME);
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}
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@ -0,0 +1,68 @@
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/* cat_noblock.c - open a file and display its contents, but exit rather than
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* wait for input */
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/* Copyright (C) 1998 by Ori Pomerantz */
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#include <stdio.h> /* standard I/O */
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#include <fcntl.h> /* for open */
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#include <unistd.h> /* for read */
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#include <stdlib.h> /* for exit */
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#include <errno.h> /* for errno */
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#define MAX_BYTES 1024*4
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main(int argc, char *argv[])
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{
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int fd; /* The file descriptor for the file to read */
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size_t bytes; /* The number of bytes read */
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char buffer[MAX_BYTES]; /* The buffer for the bytes */
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/* Usage */
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if (argc != 2) {
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printf("Usage: %s <filename>\n", argv[0]);
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puts("Reads the content of a file, but doesn't wait for input");
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exit(-1);
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}
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/* Open the file for reading in non blocking mode */
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fd = open(argv[1], O_RDONLY | O_NONBLOCK);
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/* If open failed */
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if (fd == -1) {
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if (errno = EAGAIN)
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puts("Open would block");
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else
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puts("Open failed");
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exit(-1);
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}
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/* Read the file and output its contents */
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do {
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int i;
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/* Read characters from the file */
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bytes = read(fd, buffer, MAX_BYTES);
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/* If there's an error, report it and die */
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if (bytes == -1) {
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if (errno = EAGAIN)
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puts("Normally I'd block, but you told me not to");
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else
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puts("Another read error");
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exit(-1);
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}
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/* Print the characters */
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if (bytes > 0) {
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for(i=0; i<bytes; i++)
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putchar(buffer[i]);
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}
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/* While there are no errors and the file isn't over */
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} while (bytes > 0);
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}
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