linux核心seq操作

頭檔案linux/seq_file.h

seq相關函數的實作在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實作初始化工作，在周遊一個連結對象開始時調用

stop當所有連結對象周遊結束時調用，主要完成一些清理工作

next用來在周遊中尋找下一個連結對象，傳回下一個對象或者NULL

show對周遊對象進行操作的函數主要是調用seq_printf, seq_puts之類的函數，列印出這個對象節點的資訊。

//seq操作包括以下一系列函數
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 *);      

實作例子

/*
 * 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(...)
#endif

static 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);      

參考文章

1. ​​讀取proc檔案之seq_file ​​

參考資源

1. ​​實作核心seq操作的例子​​ 其他可以參考的文章

   ​​​ http://blog.chinaunix.net/uid-28253945-id-3382865.html​​​

2. http://blog.chinaunix.net/uid-28253945-id-3382866.html