问Linux内核中的可写seq_file

EN

static char buf[4096];    
static char *limit = buf;

void *pfsw_seq_start(struct seq_file *m, loff_t *pos){
    if(*pos >= limit - buf) {
        return NULL;
    }
    char *data = buf + *pos;
    *pos = limit - buf;
    return data;
}

void pfsw_seq_stop(struct seq_file *m, void *v){ }

void *pfsw_seq_next(struct seq_file *m, void *v, loff_t *pos){ return NULL; }

int pfsw_seq_show(struct seq_file *m, void *v){
    seq_printf(m, "Data: %s\n", (char *) v);
    return 0;
}

ssize_t pfsw_seq_write(struct file *filp, const char __user * user_data, size_t sz, loff_t *off){
    if(*off < 0 || *off > sizeof buf){
        return -EINVAL;
    }
    size_t space_left_from_off = sizeof buf - (size_t) *off;
    size_t bytes_to_write = space_left_from_off <= sz ? space_left_from_off : sz;
    if(copy_from_user(buf + *off, user_data, bytes_to_write)){
        return -EAGAIN;
    }
    *off += bytes_to_write;
    if(*off > limit - buf){
        limit = buf + *off;
    }
    return bytes_to_write;
}

static const struct seq_operations seq_ops = {
    .start = pfsw_seq_start,
    .stop  = pfsw_seq_stop,
    .next  = pfsw_seq_next,
    .show  = pfsw_seq_show
};

int pfsw_seq_open(struct inode *ino, struct file *filp){ 
    return seq_open(filp, &seq_ops);
}

static const struct file_operations fops = {
    .open = pfsw_seq_open,
    .read = seq_read,
    .write = pfsw_seq_write,
    .release = seq_release,
};