seq_file, printk to pr_info, disk persistency

kernel_module/README.md

@@ -9,24 +9,26 @@
         1.  [panic](panic.c)
     1.  [params](params.c)
     1.  [fops](fops.c)
-        1. [ioctl](ioctl.c)
-        1. [poll](poll.c)
-        1. [anonymous_inode](anonymous_inode.c)
+        1.  [ioctl](ioctl.c)
+        1.  [poll](poll.c)
+        1.  [anonymous_inode](anonymous_inode.c)
+        1.  [seq_file](seq_file.c)
+            1. [seq_file_single](seq_file_inode.c)
     1.  Asynchronous
-        1. [workqueue](workqueue.c)
-        1. [sleep](sleep.c)
-        1. [kthread](kthread.c)
-        1. [kthreads](kthreads.c)
-        1. [schedule](schedule.c)
-        1. [timer](timer.c)
-        1. [work_from_work](work_from_work.c)
+        1.  [workqueue](workqueue.c)
+        1.  [sleep](sleep.c)
+        1.  [kthread](kthread.c)
+        1.  [kthreads](kthreads.c)
+        1.  [schedule](schedule.c)
+        1.  [timer](timer.c)
+        1.  [work_from_work](work_from_work.c)
     1.  [irq](irq.c)
     1.  Module dependencies
-        1. [dep](dep.c)
-        1. [dep2](dep2.c)
+        1.  [dep](dep.c)
+        1.  [dep2](dep2.c)
     1.  [character_device](character_device.c)
     1.  Hardware device drivers
-        1. [pci_min](pci_min.c)
-        1. [pci](pci.c)
-        1. [platform_device](platform_device.c)
+        1.  [pci_min](pci_min.c)
+        1.  [pci](pci.c)
+        1.  [platform_device](platform_device.c)
 1.  [user](user/)

kernel_module/fops.c

@@ -20,7 +20,7 @@ Here we use debugfs.
 #include <asm/uaccess.h> /* copy_from_user, copy_to_user */
 #include <linux/debugfs.h>
 #include <linux/errno.h> /* EFAULT */
-#include <linux/fs.h>
+#include <linux/fs.h> /* file_operations */
 #include <linux/kernel.h> /* min */
 #include <linux/module.h>
 #include <linux/printk.h> /* printk */

kernel_module/hello.c

@@ -15,13 +15,13 @@ MODULE_LICENSE("GPL");
 
 static int myinit(void)
 {
-	printk(KERN_INFO "hello init\n");
+	pr_info("hello init\n");
 	return 0;
 }
 
 static void myexit(void)
 {
-	printk(KERN_INFO "hello exit\n");
+	pr_info("hello exit\n");
 }
 
 module_init(myinit)

kernel_module/hello2.c

@@ -11,13 +11,13 @@ MODULE_LICENSE("GPL");
 
 static int myinit(void)
 {
-	printk(KERN_INFO "hello2 init\n");
+	pr_info("hello2 init\n");
 	return 0;
 }
 
 static void myexit(void)
 {
-	printk(KERN_INFO "hello2 exit\n");
+	pr_info("hello2 exit\n");
 }
 
 module_init(myinit)

kernel_module/seq_file.c

@@ -0,0 +1,90 @@
+/*
+Adapted from: http://allskyee.blogspot.co.uk/2011/12/proc-seqfile-write.html
+
+Writting trivial read fops is repetitive and error prone.
+
+The seq_file API makes the process much easier for those trivial cases.
+
+There is not write version however, as writes are more complex:
+https://stackoverflow.com/questions/30710517/how-to-implement-a-writable-proc-file-by-using-seq-file-in-a-driver-module
+*/
+
+#include <asm/uaccess.h> /* copy_from_user, copy_to_user */
+#include <linux/debugfs.h>
+#include <linux/errno.h> /* EFAULT */
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/printk.h> /* pr_info */
+#include <linux/seq_file.h> /* seq_read, seq_lseek, single_release */
+#include <uapi/linux/stat.h> /* S_IRUSR */
+
+MODULE_LICENSE("GPL");
+
+static struct dentry *debugfs_file;
+
+static void * next(struct seq_file *s, void *v, loff_t *pos)
+{
+	pr_info("next\n");
+    (*(unsigned long *)v)++;
+    (*pos)++;
+    return *pos < 3 ? v : NULL;
+}
+
+static void * start(struct seq_file *s, loff_t *pos)
+{
+    static unsigned long counter = 0;
+
+	pr_info("start pos = %llx\n", (unsigned long long)*pos);
+    if (*pos == 0) {
+        return &counter;
+	} else {
+        *pos = 0;
+        return NULL;
+    }
+}
+
+static int show(struct seq_file *s, void *v)
+{
+	pr_info("show\n");
+    seq_printf(s, "%lx\n", *(unsigned long *)v);
+    return 0;
+}
+
+static void stop(struct seq_file *s, void *v)
+{
+	pr_info("stop\n");
+}
+
+static struct seq_operations my_seq_ops = {
+    .next  = next,
+    .show  = show,
+    .start = start,
+    .stop  = stop,
+};
+
+static int open(struct inode *inode, struct file *file)
+{
+    return seq_open(file, &my_seq_ops);
+}
+
+static struct file_operations fops = {
+    .owner   = THIS_MODULE,
+    .llseek  = seq_lseek,
+    .open    = open,
+    .read    = seq_read,
+    .release = seq_release
+};
+
+static int myinit(void)
+{
+	debugfs_file = debugfs_create_file("lkmc_seq_file", S_IRUSR | S_IWUSR, NULL, NULL, &fops);
+	return 0;
+}
+
+static void myexit(void)
+{
+	debugfs_remove(debugfs_file);
+}
+
+module_init(myinit)
+module_exit(myexit)

kernel_module/seq_file_single.c

@@ -0,0 +1,49 @@
+/*
+For single reads, single_open is an even more convenient version of seq_file.
+*/
+
+#include <asm/uaccess.h> /* copy_from_user, copy_to_user */
+#include <linux/debugfs.h>
+#include <linux/errno.h> /* EFAULT */
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/printk.h> /* pr_info */
+#include <linux/seq_file.h> /* seq_read, seq_lseek, single_release */
+#include <uapi/linux/stat.h> /* S_IRUSR */
+
+MODULE_LICENSE("GPL");
+
+static struct dentry *debugfs_file;
+
+static int show(struct seq_file *m, void *v)
+{
+	seq_printf(m, "abcd\n");
+	return 0;
+}
+
+static int open(struct inode *inode, struct  file *file)
+{
+	return single_open(file, show, NULL);
+}
+
+static const struct file_operations fops = {
+	.llseek = seq_lseek,
+	.open = open,
+	.owner = THIS_MODULE,
+	.read = seq_read,
+	.release = single_release,
+};
+
+static int myinit(void)
+{
+	debugfs_file = debugfs_create_file("lkmc_seq_file", S_IRUSR | S_IWUSR, NULL, NULL, &fops);
+	return 0;
+}
+
+static void myexit(void)
+{
+	debugfs_remove(debugfs_file);
+}
+
+module_init(myinit)
+module_exit(myexit)