seq_file机制

最新推荐文章于 2023-02-25 07:08:33 发布

harvey2008

最新推荐文章于 2023-02-25 07:08:33 发布

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seq_file机制

在老版本的Linux内核中，proc文件系统有一个缺陷：如果输出内容大于1个内存页，需要多次读，因此处理起来很难。另外，如果输出内容太大，速度会比较慢。在2.6内核中，由于大量使用了seq_file功能，使得内核输出大文件信息更容易。使用seq_file需要包含头文件linux/seq_file.h，并定义一个seq_operations结构：

struct seq_operations {  
        void * (*start) (struct seq_file *m, loff_t *pos);// 指定seq_file文件的读开始位置  
        void (*stop) (struct seq_file *m, void *v);//关闭seq_file  
        // 把seq_file文件的当前读位置移动到下一个读位置  
        void * (*next) (struct seq_file *m, void *v, loff_t *pos);  
        int (*show) (struct seq_file *m, void *v);//格式化输出  
};

seq_file的常用操作接口如下：

int seq_open(struct file *, const struct seq_operations *);//打开  
ssize_t seq_read(struct file *, char __user *, size_t, loff_t *);//读  
loff_t seq_lseek(struct file *, loff_t, int);//定位  
int seq_release(struct inode *, struct file *);//释放  
int seq_escape(struct seq_file *, const char *, const char *);//写缓冲，忽略某些字符  
int seq_putc(struct seq_file *m, char c);// 把一个字符输出到seq_file文件  
int seq_puts(struct seq_file *m, const char *s);// 把一个字符串输出到seq_file文件

下面以cpuinfo为例说明seq_file在proc中的使用。

void create_seq_entry(char *name, mode_t mode, const struct file_operations *f)  
{  
    struct proc_dir_entry *entry;  
    entry = create_proc_entry(name, mode, NULL);  
    if (entry)  
        entry->proc_fops = f;  
}  
void __init proc_misc_init(void)  
{  
    …  
    create_seq_entry("cpuinfo", 0, &proc_cpuinfo_operations); //创建/proc目录  
}

定义proc_cpuinfo_operations：

static const struct file_operations proc_cpuinfo_operations = {  
    .open   = cpuinfo_open,  
    .read       = seq_read,  
    .llseek = seq_lseek,  
    .release    = seq_release,  
};

接下来看cpuinfo_open：

static int cpuinfo_open(struct inode *inode, struct file *file)  
{  
    return seq_open(file, &cpuinfo_op);  
}

cpuinfo_op是与硬件平台相关的。ARM的cpuinfo_op在/arc/arm/kernel/setup.c中：

struct seq_operations cpuinfo_op = {  
    .start  = c_start,  
    .next   = c_next,  
    .stop   = c_stop,  
    .show= c_show 
};

cpuinfo_op就是实际上对/proc/ cpuinfo进行修改的操作接口，其中最重要的是c_show：

static int c_show(struct seq_file *m, void *v)  
{  
    int i;  
    seq_printf(m, "Processor\t: %s rev %d (%s)\n",  
           cpu_name, (int)processor_id & 15, elf_platform);  
#if defined(CONFIG_SMP)//针对多处理器  
    for_each_online_cpu(i) {  
        seq_printf(m, "processor\t: %d\n", i);  
        seq_printf(m, "BogoMIPS\t: %lu.%02lu\n\n",  
               per_cpu(cpu_data, i).loops_per_jiffy / (500000UL/HZ),  
               (per_cpu(cpu_data, i).loops_per_jiffy / (5000UL/HZ)) % 100);  
    }  
#else /* CONFIG_SMP */  
    seq_printf(m, "BogoMIPS\t: %lu.%02lu\n",  
           loops_per_jiffy / (500000/HZ),  
           (loops_per_jiffy / (5000/HZ)) % 100);  
#endif  
    seq_puts(m, "Features\t: ");  
    for (i = 0; hwcap_str[i]; i++)  
        if (elf_hwcap & (1 << i))  
            seq_printf(m, "%s ", hwcap_str[i]);  
    seq_printf(m, "\nCPU implementer\t: 0x%02x\n", processor_id >> 24);  
    seq_printf(m, "CPU architecture: %s\n", proc_arch[cpu_architecture()]);  
    if ((processor_id & 0x0008f000) == 0x00000000) {/* pre-ARM7 */  
        seq_printf(m, "CPU part\t: %07x\n", processor_id >> 4);  
    } else {  
        if ((processor_id & 0x0008f000) == 0x00007000) {/* ARM7 */  
            seq_printf(m, "CPU variant\t: 0x%02x\n",  
                   (processor_id >> 16) & 127);  
        } else {/* ARM7以上的CPU */  
            seq_printf(m, "CPU variant\t: 0x%x\n",  
                   (processor_id >> 20) & 15);  
        }  
        seq_printf(m, "CPU part\t: 0x%03x\n",(processor_id >> 4) & 0xfff);  
    }  
    seq_printf(m, "CPU revision\t: %d\n", processor_id & 15);  
    {  
        unsigned int cache_info = read_cpuid(CPUID_CACHETYPE);  
        if (cache_info != processor_id) {  
            seq_printf(m, "Cache type\t: %s\n"  
                      "Cache clean\t: %s\n"  
                      "Cache lockdown\t: %s\n"  
                      "Cache format\t: %s\n",  
                   cache_types[CACHE_TYPE(cache_info)],  
                   cache_clean[CACHE_TYPE(cache_info)],  
                   cache_lockdown[CACHE_TYPE(cache_info)],  
                   CACHE_S(cache_info) ? "Harvard" : "Unified");  
            if (CACHE_S(cache_info)) {  
                c_show_cache(m, "I", CACHE_ISIZE(cache_info));  
                c_show_cache(m, "D", CACHE_DSIZE(cache_info));  
            } else {  
                c_show_cache(m, "Cache", CACHE_ISIZE(cache_info));  
            }  
        }  
    }  
    seq_puts(m, "\n");  
    seq_printf(m, "Hardware\t: %s\n", machine_name);  
    seq_printf(m, "Revision\t: %04x\n", system_rev);  
    seq_printf(m, "Serial\t\t: %08x%08x\n",system_serial_high, system_serial_low);  
    return 0;  
}