linux内核seq操作

头文件linux/seq_file.h
seq相关函数的实现在fs/seq_file.c

struct seq_file {        char *buf;        size_t size;        size_t from;        size_t count;        loff_t index;        loff_t read_pos;        u64 version;        struct mutex lock;        const struct seq_operations *op;        int poll_event;        void *private;};

struct seq_operations {        void * (*start) (struct seq_file *m, loff_t *pos);        void (*stop) (struct seq_file *m, void *v);        void * (*next) (struct seq_file *m, void *v, loff_t *pos);        int (*show) (struct seq_file *m, void *v);};

start实现初始化工作，在遍历一个链接对象开始时调用
stop当所有链接对象遍历结束时调用，主要完成一些清理工作
next用来在遍历中寻找下一个链接对象，返回下一个对象或者NULL
show对遍历对象进行操作的函数主要是调用seq_printf, seq_puts之类的函数，打印出这个对象节点的信息。

//seq操作包括以下一系列函数int seq_open(struct file *, const struct seq_operations *);ssize_t seq_read(struct file *, char __user *, size_t, loff_t *);loff_t seq_lseek(struct file *, loff_t, int);int seq_release(struct inode *, struct file *);

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实现例子

/* * Documentation/filesystem/seq_file.txt */ #include <linux/kernel.h>#include <linux/module.h>#include <linux/init.h>#include <linux/mm.h>#include <linux/fs.h>#include <linux/slab.h>#include <linux/proc_fs.h>#include <linux/seq_file.h>//#define DEBUG_SEQ#ifdef DEBUG_SEQ#define log_seq(...) printk(__VA_ARGS__)#else#define log_seq(...)#endifstatic void *ct_seq_start(struct seq_file *s, loff_t *pos){        int *count = s->private;        log_seq("%s\n", __func__);        if ((long long)*pos < *count) {                printk("start pos %lld\n", (long long)*pos);                return pos;        }        return NULL;}static void *ct_seq_next(struct seq_file *s, void *v, loff_t *pos){        int *count = s->private;        log_seq("%s\n", __func__);        ++*pos;        if ((long long)*pos < *count) {                printk("next pos %lld\n", (long long)*pos);                return pos;        }        return NULL;}static void ct_seq_stop(struct seq_file *s, void *v){        log_seq("%s\n", __func__);}static int ct_seq_show(struct seq_file *s, void *v){        loff_t *pos = v;        log_seq("%s\n", __func__);        seq_printf(s, "%lld\n", (long long)*pos);        return 0;}static const struct seq_operations ct_seq_ops = {        .start = ct_seq_start,        .next = ct_seq_next,        .stop = ct_seq_stop,        .show = ct_seq_show};static int ct_open(struct inode *inode, struct file *file){        int ret;        struct seq_file *s;        ret = seq_open(file, &ct_seq_ops);        s = file->private_data;        s->private = (void *)kmalloc(sizeof(int), GFP_KERNEL);        *((int *)s->private) = 5;        return ret;}static int ct_close(struct inode *inode, struct file *file){        struct seq_file *s = file->private_data;        kfree(s->private);        return seq_release(inode, file);}static const struct file_operations ct_file_ops = {        .owner = THIS_MODULE,        .open = ct_open,        .read = seq_read,//      .write = seq_write,        .llseek = seq_lseek,        .release = ct_close};static int __init ct_init(void){        struct proc_dir_entry *entry;        entry = proc_create("sequence", 0, NULL, &ct_file_ops);        return 0;}static void __exit ct_exit(void){        remove_proc_entry("sequence", NULL);}module_init(ct_init);module_exit(ct_exit);

整体看来，用户态调用一次读操作，seq_file流程为：该函数调用struct seq_operations结构提顺序为：start->show->next->show…->next->show->next->stop->start->stop来读取文件

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参考文章

1. 读取proc文件之seq_file

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参考资源

1. 实现内核seq操作的例子