seq_file学习（2）—— seq_file

li {list-style-type:decimal;}ol.wiz-list-level2 > li {list-style-type:lower-latin;}ol.wiz-list-level3 > li {list-style-type:lower-roman;}blockquote {padding:0 12px;padding:0 0.75rem;}blockquote > :first-child {margin-top:0;}blockquote > :last-child {margin-bottom:0;}img {border:0;max-width:100%;height:auto !important;margin:2px 0;}table {border-collapse:collapse;border:1px solid #bbbbbb;}td, th {padding:4px 8px;border-collapse:collapse;border:1px solid #bbbbbb;min-height:28px;word-break:break-all;box-sizing: border-box;}.wiz-hide {display:none !important;}
-->
span::selection, .CodeMirror-line > span > span::selection { background: #d7d4f0; }.CodeMirror-line::-moz-selection, .CodeMirror-line > span::-moz-selection, .CodeMirror-line > span > span::-moz-selection { background: #d7d4f0; }.cm-searching {background: #ffa; background: rgba(255, 255, 0, .4);}.cm-force-border { padding-right: .1px; }@media print { .CodeMirror div.CodeMirror-cursors {visibility: hidden;}}.cm-tab-wrap-hack:after { content: ""; }span.CodeMirror-selectedtext { background: none; }.CodeMirror-activeline-background, .CodeMirror-selected {transition: visibility 0ms 100ms;}.CodeMirror-blur .CodeMirror-activeline-background, .CodeMirror-blur .CodeMirror-selected {visibility:hidden;}.CodeMirror-blur .CodeMirror-matchingbracket {color:inherit !important;outline:none !important;text-decoration:none !important;}
-->

作者

彭东林

pengdonglin137@163.com

 

平台

Linux-4.14.13

Qemu + vexpress

 

概述

前面介绍了single_open，下面结合一个简单的demo驱动，学习一下seq_file的用法。

下面是一张示意图：

 

正文

seq_demo驱动里实现了一个简单的链表，在init的时候会依次创建7个节点并加入链表，然后向用户空间导出一个seq_demo的节点，读取这个节点，就会调用seq_file相关函数对链表进行遍历，输出每个节点的相关信息。

一、seq_demo驱动

#include <linux/init.h>
#include <linux/module.h>
#include <linux/seq_file.h>
#include <linux/debugfs.h>
#include <linux/fs.h>
#include <linux/list.h>
#include <linux/slab.h>

static struct dentry *seq_demo_dir;
static LIST_HEAD(seq_demo_list);
static DEFINE_MUTEX(seq_demo_lock);

struct seq_demo_node {
char name[10];
struct list_head list;
};

static void *seq_demo_start(struct seq_file *s, loff_t *pos)
{
mutex_lock(&seq_demo_lock);

return seq_list_start(&seq_demo_list, *pos);
}

static void *seq_demo_next(struct seq_file *s, void *v, loff_t *pos)
{
return seq_list_next(v, &seq_demo_list, pos);
}

static void seq_demo_stop(struct seq_file *s, void *v)
{
mutex_unlock(&seq_demo_lock);
}

static int seq_demo_show(struct seq_file *s, void *v)
{
struct seq_demo_node *node = list_entry(v, struct seq_demo_node, list);

seq_printf(s, "name: %s, addr: 0x%p\n", node->name, node);

return 0;
}

static const struct seq_operations seq_demo_ops = {
.start = seq_demo_start,
.next = seq_demo_next,
.stop = seq_demo_stop,
.show = seq_demo_show,
};

static int seq_demo_open(struct inode *inode, struct file *file)
{
return seq_open(file, &seq_demo_ops);
}

static const struct file_operations seq_demo_fops = {
.owner = THIS_MODULE,
.open = seq_demo_open,
.read = seq_read,
.llseek = seq_lseek,
.release = seq_release,
};

static int __init seq_demo_init(void)
{
int i;
struct seq_demo_node *node;

for (i = 0; i < 7; i++) {
node = kzalloc(sizeof(struct seq_demo_node), GFP_KERNEL);
sprintf(node->name, "node%d", i);

INIT_LIST_HEAD(&node->list);
list_add_tail(&node->list, &seq_demo_list);
}

seq_demo_dir = debugfs_create_file("seq_demo", 0444, NULL,
NULL, &seq_demo_fops);
return 0;
}

static void __exit seq_demo_exit(void)
{
struct seq_demo_node *node_pos, *node_n;

if (seq_demo_dir) {
debugfs_remove(seq_demo_dir);
list_for_each_entry_safe(node_pos, node_n, &seq_demo_list, list)
if (node_pos) {
printk("%s: release %s\n", __func__, node_pos->name);
kfree(node_pos);
}
}
}

module_init(seq_demo_init);
module_exit(seq_demo_exit);
MODULE_LICENSE("GPL");

 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/seq_file.h>
 #include <linux/debugfs.h>
 #include <linux/fs.h>
 #include <linux/list.h>
 #include <linux/slab.h>

 static struct dentry *seq_demo_dir;
 static LIST_HEAD(seq_demo_list);
 static DEFINE_MUTEX(seq_demo_lock);

 struct seq_demo_node {
     char name[];
     struct list_head list;
 };

 static void *seq_demo_start(struct seq_file *s, loff_t *pos)
 {
     mutex_lock(&seq_demo_lock);

     return seq_list_start(&seq_demo_list, *pos);
 }

 static void *seq_demo_next(struct seq_file *s, void *v, loff_t *pos)
 {
     return seq_list_next(v, &seq_demo_list, pos);
 }

 static void seq_demo_stop(struct seq_file *s, void *v)
 {
     mutex_unlock(&seq_demo_lock);
 }

 static int seq_demo_show(struct seq_file *s, void *v)
 {
     struct seq_demo_node *node = list_entry(v, struct seq_demo_node, list);

     seq_printf(s, "name: %s, addr: 0x%p\n", node->name, node);

     return ;
 }

 static const struct seq_operations seq_demo_ops = {
     .start = seq_demo_start,
     .next = seq_demo_next,
     .stop = seq_demo_stop,
     .show = seq_demo_show,
 };

 static int seq_demo_open(struct inode *inode, struct file *file)
 {
     return seq_open(file, &seq_demo_ops);
 }

 static const struct file_operations seq_demo_fops = {
     .owner = THIS_MODULE,
     .open = seq_demo_open,
     .read = seq_read,
     .llseek = seq_lseek,
     .release = seq_release,
 };

 static int __init seq_demo_init(void)
 {
     int i;
     struct seq_demo_node *node;

     for (i = ; i < ; i++) {
         node = kzalloc(sizeof(struct seq_demo_node), GFP_KERNEL);
         sprintf(node->name, "node%d", i);

         INIT_LIST_HEAD(&node->list);
         list_add_tail(&node->list, &seq_demo_list);
     }

     seq_demo_dir = debugfs_create_file("seq_demo", , NULL,
         NULL, &seq_demo_fops);
     return ;
 }

 static void __exit seq_demo_exit(void)
 {
     struct seq_demo_node *node_pos, *node_n;

     if (seq_demo_dir) {
         debugfs_remove(seq_demo_dir);
         list_for_each_entry_safe(node_pos, node_n, &seq_demo_list, list)
             if (node_pos) {
                 printk("%s: release %s\n", __func__, node_pos->name);
                 kfree(node_pos);
             }
     }
 }

 module_init(seq_demo_init);
 module_exit(seq_demo_exit);
 MODULE_LICENSE("GPL");

下面是运行结果：

[root@vexpress mnt]# cat /d/seq_demo
name: node0, addr: 0xef252000
name: node1, addr: 0xef252680
name: node2, addr: 0xef252380
name: node3, addr: 0xef252740
name: node4, addr: 0xef252b00
name: node5, addr: 0xee80e480
name: node6, addr: 0xeeb9fd40
name: node7, addr: 0xeeb9fd00

二、分析

在遍历链表的时候使用seq_file提供的通用接口函数，当然也可以自己实现，只需要遵循如下原则：

start：根据索引编号pos找到对应的node，并返回该node的地址，也就是show和next方法里的v

next：根据当前node的地址和索引编号计算下一个node的地址和索引编号pos，返回值就是下一个节点的地址

show：输出传入的node的信息

stop：如果在start里有加锁，那么在这里需要释放锁

 

结合上面的驱动分析一下：

seq_list_start：

 struct list_head *seq_list_start(struct list_head *head, loff_t pos)
 {
     struct list_head *lh;

     list_for_each(lh, head)
         if (pos-- == )
             return lh;

     return NULL;
 }

遍历链表，寻找索引为pos的项，找到的话，返回地址，否则返回NULL。当返回NULL的时候， stop会被调用。

 

seq_list_next：

 struct list_head *seq_list_next(void *v, struct list_head *head, loff_t *ppos)
 {
     struct list_head *lh;

     lh = ((struct list_head *)v)->next;
     ++*ppos;
     return lh == head ? NULL : lh;
 }

计算下一项的地址和索引，如果遍历结束，即lh==head，返回NULL，否则返回下一项的地址。当返回NULL的时候，stop会被调用并把缓冲区中的内容吐给用户

 

 

未完待续