/* * procfs4.c - create a "file" in /proc * This program uses the seq_file library to manage the /proc file. */ #include /* We are doing kernel work */ #include /* Specifically, a module */ #include /* Necessary because we use proc fs */ #include /* for seq_file */ #include #if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 6, 0) #define HAVE_PROC_OPS #endif #define PROC_NAME "iter" /* This function is called at the beginning of a sequence. * ie, when: * - the /proc file is read (first time) * - after the function stop (end of sequence) */ static void *my_seq_start(struct seq_file *s, loff_t *pos) { static unsigned long counter = 0; /* beginning a new sequence? */ if (*pos == 0) { /* yes => return a non null value to begin the sequence */ return &counter; } /* no => it is the end of the sequence, return end to stop reading */ *pos = 0; return NULL; } /* This function is called after the beginning of a sequence. * It is called untill the return is NULL (this ends the sequence). */ static void *my_seq_next(struct seq_file *s, void *v, loff_t *pos) { unsigned long *tmp_v = (unsigned long *)v; (*tmp_v)++; (*pos)++; return NULL; } /* This function is called at the end of a sequence. */ static void my_seq_stop(struct seq_file *s, void *v) { /* nothing to do, we use a static value in start() */ } /* This function is called for each "step" of a sequence. */ static int my_seq_show(struct seq_file *s, void *v) { loff_t *spos = (loff_t *)v; seq_printf(s, "%Ld\n", *spos); return 0; } /* This structure gather "function" to manage the sequence */ static struct seq_operations my_seq_ops = { .start = my_seq_start, .next = my_seq_next, .stop = my_seq_stop, .show = my_seq_show, }; /* This function is called when the /proc file is open. */ static int my_open(struct inode *inode, struct file *file) { return seq_open(file, &my_seq_ops); }; /* This structure gather "function" that manage the /proc file */ #ifdef HAVE_PROC_OPS static const struct proc_ops my_file_ops = { .proc_open = my_open, .proc_read = seq_read, .proc_lseek = seq_lseek, .proc_release = seq_release, }; #else static const struct file_operations my_file_ops = { .open = my_open, .read = seq_read, .llseek = seq_lseek, .release = seq_release, }; #endif static int __init procfs4_init(void) { struct proc_dir_entry *entry; entry = proc_create(PROC_NAME, 0, NULL, &my_file_ops); if (entry == NULL) { remove_proc_entry(PROC_NAME, NULL); pr_debug("Error: Could not initialize /proc/%s\n", PROC_NAME); return -ENOMEM; } return 0; } static void __exit procfs4_exit(void) { remove_proc_entry(PROC_NAME, NULL); pr_debug("/proc/%s removed\n", PROC_NAME); } module_init(procfs4_init); module_exit(procfs4_exit); MODULE_LICENSE("GPL");