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);elseseq_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_64if (c->x86_tlbsize > 0)seq_printf(m, "TLB size\t: %d 4K pages\n", c->x86_tlbsize);#endifseq_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]);elseseq_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_HIGHMEMK(i.totalhigh),K(i.freehigh),K(i.totalram-i.totalhigh),K(i.freeram-i.freehigh),#endif#ifndef CONFIG_MMUK((unsigned long) atomic_long_read(&mmap_pages_allocated)),#endifK(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_QUICKLISTK(quicklist_total_size()),#endifK(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}