linux设备驱动学习笔记--内核调试方法之proc（补充seq_file）

上一节中的proc实现对于开关文件，控制文件，以及显示很少信息的文件来说还是比较简单的，但是对于需要输出大量信息像meminfo，或者结构化的信息像cpuinfo等时就会显得很笨拙，并且代码也很不好理解与维护。内核为了简化这种proc文件的实现提供了另外一种方案----seq_file接口。

set_file 接口假定你在创建一个虚拟文件, 它涉及一系列的必须返回给用户空间的项. 为使用 seq_file, 你必须创建一个简单的 "iterator" 对象, 它能在序列里建立一个位置(start), 向前进(next), 并且输出序列里的一个项(show). 它可能听起来复杂,但实际上过程非常简单.

seq_file接口即可以实现以前的非结构化的信息显示，也可以实现结构化的信息显示，并且两种实现的代码都比较简单清晰。使用seq_file接口需要包含头文件<linux/seq_file.h>。

seq_file的使用比较规范，与其他文件操作步骤比较一致，所以看起来也比较容易，我们可以通过分析内核中对meminfo和cpuinfo来学习非结构化与结构化信息显示的实现步骤。

1，结构化信息显示方式

第一步：在模块初始化时调用proc_create来创建相应proc文件

static int __init proc_cpuinfo_init(void)
{
	proc_create("cpuinfo", 0, NULL, &proc_cpuinfo_operations);
	return 0;
}

第二步：在模块卸载时调用remove_proc_entry函数删除相应的proc文件，当然因为cpuinfo的实现在内核代码中，不涉及到卸载，所以cpuinfo没有删除相应proc文件的操作，但是我们自己编写的内核模块涉及此场景，所以需要实现此步骤。

第三步：定义file_operations结构体（第一步中创建时会使用）

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

第四步，实现file_operations的open函数，在open函数中建议proc文件与seq_file机制的四个迭代器的联系。而read、llseek、release等都是seq_file实现好的框架，不需要另外实现。

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

第五步，定义seq_operations结构体

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

第六步，实现迭代器（start/next/stop/show），按自己需要来实现，这里只是cpuinfo的实现

start迭代器：

static void *c_start(struct seq_file *m, loff_t *pos)
{
	*pos = cpumask_next(*pos - 1, cpu_online_mask);
	if ((*pos) < nr_cpu_ids)
		return &cpu_data(*pos);
	return NULL;
}

next迭代器：

static void *c_next(struct seq_file *m, void *v, loff_t *pos)
{
	(*pos)++;
	return c_start(m, pos);
}

stop迭代器，一般实现为空

static void c_stop(struct seq_file *m, void *v)
{
}

show迭代器，最主要的信息显示

static int show_cpuinfo(struct seq_file *m, void *v)
{
	struct cpuinfo_x86 *c = v;
	unsigned int cpu;
	int i;

	cpu = c->cpu_index;
	seq_printf(m, "processor\t: %u\n"
		   "vendor_id\t: %s\n"
		   "cpu family\t: %d\n"
		   "model\t\t: %u\n"
		   "model name\t: %s\n",
		   cpu,
		   c->x86_vendor_id[0] ? c->x86_vendor_id : "unknown",
		   c->x86,
		   c->x86_model,
		   c->x86_model_id[0] ? c->x86_model_id : "unknown");

	if (c->x86_mask || c->cpuid_level >= 0)
		seq_printf(m, "stepping\t: %d\n", c->x86_mask);
	else
		seq_printf(m, "stepping\t: unknown\n");
	if (c->microcode)
		seq_printf(m, "microcode\t: 0x%x\n", c->microcode);

	if (cpu_has(c, X86_FEATURE_TSC)) {
		unsigned int freq = cpufreq_quick_get(cpu);

		if (!freq)
			freq = cpu_khz;
		seq_printf(m, "cpu MHz\t\t: %u.%03u\n",
			   freq / 1000, (freq % 1000));
	}

	/* Cache size */
	if (c->x86_cache_size >= 0)
		seq_printf(m, "cache size\t: %d KB\n", c->x86_cache_size);

	show_cpuinfo_core(m, c, cpu);
	show_cpuinfo_misc(m, c);

	seq_printf(m, "flags\t\t:");
	for (i = 0; i < 32*NCAPINTS; i++)
		if (cpu_has(c, i) && x86_cap_flags[i] != NULL)
			seq_printf(m, " %s", x86_cap_flags[i]);

	seq_printf(m, "\nbogomips\t: %lu.%02lu\n",
		   c->loops_per_jiffy/(500000/HZ),
		   (c->loops_per_jiffy/(5000/HZ)) % 100);

#ifdef CONFIG_X86_64
	if (c->x86_tlbsize > 0)
		seq_printf(m, "TLB size\t: %d 4K pages\n", c->x86_tlbsize);
#endif
	seq_printf(m, "clflush size\t: %u\n", c->x86_clflush_size);
	seq_printf(m, "cache_alignment\t: %d\n", c->x86_cache_alignment);
	seq_printf(m, "address sizes\t: %u bits physical, %u bits virtual\n",
		   c->x86_phys_bits, c->x86_virt_bits);

	seq_printf(m, "power management:");
	for (i = 0; i < 32; i++) {
		if (c->x86_power & (1 << i)) {
			if (i < ARRAY_SIZE(x86_power_flags) &&
			    x86_power_flags[i])
				seq_printf(m, "%s%s",
					   x86_power_flags[i][0] ? " " : "",
					   x86_power_flags[i]);
			else
				seq_printf(m, " [%d]", i);
		}
	}

	seq_printf(m, "\n\n");

	return 0;
}

2，非结构化信息显示方式

第一步：在模块初始化时调用proc_create来创建相应proc文件

static int __init proc_meminfo_init(void)
{
	proc_create("meminfo", 0, NULL, &meminfo_proc_fops);
	return 0;
}

第二步：在模块卸载时调用remove_proc_entry函数删除相应的proc文件，当然因为meminfo的实现在内核代码中，不涉及到卸载，所以meminfo没有删除相应proc文件的操作，但是我们自己编写的内核模块涉及此场景，所以需要实现此步骤。

第三步：定义file_operations结构体（第一步中创建时会使用）

static const struct file_operations meminfo_proc_fops = {
	.open		= meminfo_proc_open,
	.read		= seq_read,
	.llseek		= seq_lseek,
	.release	= single_release,
};

第四步，实现file_operations的open函数，因为meminfo是非结构化信息显示，所以我们不需要实现start/next/stop等迭代器，只需要实现show来显示信息即可，所以不需要像cpuinfo一样需要定义一个seq_operations结构体并且调用seq_open来建立proc文件与seq_file迭代器之间的联系。seq_file接口对于非结构化的信息显示情况提供了一个single_open接口，所以在open中调用single_open。

static int meminfo_proc_open(struct inode *inode, struct file *file)
{
	return single_open(file, meminfo_proc_show, NULL);
}

第五步，只需要实现show迭代器meminfo_proc_show即可

static int meminfo_proc_show(struct seq_file *m, void *v)
{
	struct sysinfo i;
	unsigned long committed;
	unsigned long allowed;
	struct vmalloc_info vmi;
	long cached;
	unsigned long pages[NR_LRU_LISTS];
	int lru;

/*
 * display in kilobytes.
 */
#define K(x) ((x) << (PAGE_SHIFT - 10))
	si_meminfo(&i);
	si_swapinfo(&i);
	committed = percpu_counter_read_positive(&vm_committed_as);
	allowed = ((totalram_pages - hugetlb_total_pages())
		* sysctl_overcommit_ratio / 100) + total_swap_pages;

	cached = global_page_state(NR_FILE_PAGES) -
			total_swapcache_pages - i.bufferram;
	if (cached < 0)
		cached = 0;

	get_vmalloc_info(&vmi);

	for (lru = LRU_BASE; lru < NR_LRU_LISTS; lru++)
		pages[lru] = global_page_state(NR_LRU_BASE + lru);

	/*
	 * Tagged format, for easy grepping and expansion.
	 */
	seq_printf(m,
		"MemTotal:       %8lu kB\n"
		"MemFree:        %8lu kB\n"
		"Buffers:        %8lu kB\n"
		"Cached:         %8lu kB\n"
		"SwapCached:     %8lu kB\n"
		"Active:         %8lu kB\n"
		"Inactive:       %8lu kB\n"
		"Active(anon):   %8lu kB\n"
		"Inactive(anon): %8lu kB\n"
		"Active(file):   %8lu kB\n"
		"Inactive(file): %8lu kB\n"
		"Unevictable:    %8lu kB\n"
		"Mlocked:        %8lu kB\n"
#ifdef CONFIG_HIGHMEM
		"HighTotal:      %8lu kB\n"
		"HighFree:       %8lu kB\n"
		"LowTotal:       %8lu kB\n"
		"LowFree:        %8lu kB\n"
#endif
#ifndef CONFIG_MMU
		"MmapCopy:       %8lu kB\n"
#endif
		"SwapTotal:      %8lu kB\n"
		"SwapFree:       %8lu kB\n"
		"Dirty:          %8lu kB\n"
		"Writeback:      %8lu kB\n"
		"AnonPages:      %8lu kB\n"
		"Mapped:         %8lu kB\n"
		"Shmem:          %8lu kB\n"
		"Slab:           %8lu kB\n"
		"SReclaimable:   %8lu kB\n"
		"SUnreclaim:     %8lu kB\n"
		"KernelStack:    %8lu kB\n"
		"PageTables:     %8lu kB\n"
#ifdef CONFIG_QUICKLIST
		"Quicklists:     %8lu kB\n"
#endif
		"NFS_Unstable:   %8lu kB\n"
		"Bounce:         %8lu kB\n"
		"WritebackTmp:   %8lu kB\n"
		"CommitLimit:    %8lu kB\n"
		"Committed_AS:   %8lu kB\n"
		"VmallocTotal:   %8lu kB\n"
		"VmallocUsed:    %8lu kB\n"
		"VmallocChunk:   %8lu kB\n"
#ifdef CONFIG_MEMORY_FAILURE
		"HardwareCorrupted: %5lu kB\n"
#endif
		,
		K(i.totalram),
		K(i.freeram),
		K(i.bufferram),
		K(cached),
		K(total_swapcache_pages),
		K(pages[LRU_ACTIVE_ANON]   + pages[LRU_ACTIVE_FILE]),
		K(pages[LRU_INACTIVE_ANON] + pages[LRU_INACTIVE_FILE]),
		K(pages[LRU_ACTIVE_ANON]),
		K(pages[LRU_INACTIVE_ANON]),
		K(pages[LRU_ACTIVE_FILE]),
		K(pages[LRU_INACTIVE_FILE]),
		K(pages[LRU_UNEVICTABLE]),
		K(global_page_state(NR_MLOCK)),
#ifdef CONFIG_HIGHMEM
		K(i.totalhigh),
		K(i.freehigh),
		K(i.totalram-i.totalhigh),
		K(i.freeram-i.freehigh),
#endif
#ifndef CONFIG_MMU
		K((unsigned long) atomic_long_read(&mmap_pages_allocated)),
#endif
		K(i.totalswap),
		K(i.freeswap),
		K(global_page_state(NR_FILE_DIRTY)),
		K(global_page_state(NR_WRITEBACK)),
		K(global_page_state(NR_ANON_PAGES)),
		K(global_page_state(NR_FILE_MAPPED)),
		K(global_page_state(NR_SHMEM)),
		K(global_page_state(NR_SLAB_RECLAIMABLE) +
				global_page_state(NR_SLAB_UNRECLAIMABLE)),
		K(global_page_state(NR_SLAB_RECLAIMABLE)),
		K(global_page_state(NR_SLAB_UNRECLAIMABLE)),
		global_page_state(NR_KERNEL_STACK) * THREAD_SIZE / 1024,
		K(global_page_state(NR_PAGETABLE)),
#ifdef CONFIG_QUICKLIST
		K(quicklist_total_size()),
#endif
		K(global_page_state(NR_UNSTABLE_NFS)),
		K(global_page_state(NR_BOUNCE)),
		K(global_page_state(NR_WRITEBACK_TEMP)),
		K(allowed),
		K(committed),
		(unsigned long)VMALLOC_TOTAL >> 10,
		vmi.used >> 10,
		vmi.largest_chunk >> 10
#ifdef CONFIG_MEMORY_FAILURE
		,atomic_long_read(&mce_bad_pages) << (PAGE_SHIFT - 10)
#endif
		);

	hugetlb_report_meminfo(m);

	arch_report_meminfo(m);

	return 0;
#undef K
}