Using seq file to print out linux tasks

Change-Id: I92ab5fbbad79ae984a5151ffff96749f7ac431d0

debug/platform_driver_test/Makefile

@@ -17,6 +17,7 @@ endif
 obj-m := skeleton_ss.o
 obj-m += kset_skeleton.o
 obj-m += seq_test.o
+obj-m += seq_test2.o
 
 KERNEL_DIR ?= /lib/modules/$(shell uname -r)/build
 KERNEL_BUID_OUTPUT ?=$(KERNEL_DIR)

debug/platform_driver_test/seq_test2.c

@@ -0,0 +1,167 @@
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/percpu.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/debugfs.h>
+
+#define TEST_NODE_NAME "showtask"
+#define TEST_DIR_NAME "tasks"
+
+#ifdef PROC_FS_TEST
+static struct proc_dir_entry *entry;
+#endif
+
+static loff_t *gpos = NULL;
+struct dentry *d_dir_name;
+
+/*
+ *The pos passed to start() will always be either zero, or
+ *the most recent pos used in the previous session.
+ */
+static void *myseq_start(struct seq_file *m, loff_t *pos)
+{
+	int i;
+	struct task_struct *task;
+	gpos = pos;
+
+	/*
+	 * 传入start的参数pos要么是0,要么是上一次会话的pos值
+	 * start从position 0开始(pos = 0),意味着从文件开始
+	 * 可以在此时打印文件头
+	 */
+	if (*pos == 0) {
+		seq_printf(m, "Current all the processes in system:\n"
+				"%-24s%-5s\n", "name", "pid");
+#ifdef PROC_FS_TEST
+		task = &init_task;
+#else
+		task = m->private;
+#endif
+		pr_debug("start first:%-24s%-5d\n", task->comm, task->pid);
+		return task;
+	} else {
+		/* linux中task被挂入到环形链表中 */
+#ifdef PROC_FS_TEST
+		for (i = 0, task = &init_task; i < *pos; i++)
+#else
+		for (i = 0, task = m->private; i < *pos; i++)
+#endif
+			task = next_task(task);
+		BUG_ON(i != *pos);
+
+		/* 读完所有内容, 结束 */
+#ifdef PROC_FS_TEST
+		if (task == &init_task)
+#else
+		if (task == m->private)
+#endif
+			return NULL;
+
+		pr_debug("start return %-24s%-5d\n", task->comm, task->pid);
+		return task;
+	}
+}
+
+/*
+ * 1. 每执行一次都要步进一次position
+ * 2. 将返回值传递给show作为第二个参数
+ * 参数p是当前会话中start的返回值的下一个内容
+ */
+static void *myseq_next(struct seq_file *m, void *p, loff_t *pos)
+{
+	struct task_struct * task = (struct task_struct *)p;
+
+	task = next_task(task);
+
+	/* step forward, must update position before return NULL */
+	++(*pos);
+#ifdef PROC_FS_TEST
+	if ((*pos != 0) && (task == &init_task))
+#else
+	if ((*pos != 0) && (task == m->private))
+#endif
+		return NULL;
+
+	return task;
+}
+
+/* 执行了stop说明结束一次会话,下次绘画从这个pos重新开始 */
+static void myseq_stop(struct seq_file *m, void *p)
+{
+	struct task_struct * task = (struct task_struct *)p;
+	if (task != NULL)
+		pr_debug("stop->:%-24s%-5d, pos: %lld\n", task->comm, task->pid, *gpos);
+}
+
+/*
+ * 第二个参数是当前会话中start或next的返回值
+ * 第一次是start的返回值
+ * 使用过程中是next或是start的返回值
+ */
+static int myseq_show(struct seq_file *m, void *p)
+{
+	struct task_struct * task = (struct task_struct *)p;
+	seq_printf(m, "%-24s%-5d\n", task->comm, task->pid);
+
+	return 0;
+}
+
+static struct seq_operations myseq_sops = {
+	.start = myseq_start,
+	.next  = myseq_next,
+	.stop  = myseq_stop,
+	.show  = myseq_show
+};
+
+#ifdef PROC_FS_TEST
+static int myseq_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &myseq_sops);
+}
+
+static const struct proc_ops proc_fops = {
+	.proc_open = myseq_open,
+	.proc_read = seq_read,
+	.proc_lseek = seq_lseek,
+	.proc_release = seq_release,
+};
+#endif
+
+#ifndef PROC_FS_TEST
+DEFINE_SEQ_ATTRIBUTE(myseq);
+#endif
+static int seq_test_init(void)
+{
+#ifdef PROC_FS_TEST
+	entry = proc_create(TEST_NODE_NAME, 0444, NULL, &proc_fops);
+	if (!entry)
+		printk(KERN_EMERG "proc_create error.\n");
+#else
+	d_dir_name = debugfs_create_dir(TEST_DIR_NAME, NULL);
+	/*
+	 * 第四个参数就是赋值给s->private的
+	 * init_task是内核中的全局变量,初始化为第一个进程swapper或是idel
+	 * 内核中将所有进程都挂载在环形链表中
+	 * 这里将init_task作为参数传递给seq_file->private
+	 */
+	debugfs_create_file(TEST_NODE_NAME, 0444, d_dir_name, &init_task,
+			&myseq_fops);
+#endif
+	return 0;
+}
+
+static void seq_test_exit(void)
+{
+#ifdef PROC_FS_TEST
+	remove_proc_entry(TEST_NODE_NAME, NULL);
+#else
+	debugfs_remove(d_dir_name);
+#endif
+}
+
+module_init(seq_test_init);
+module_exit(seq_test_exit);
+MODULE_LICENSE("GPL");