struct resource ioport_resource = {
	.name	= "PCI IO",
	.start	= 0,
	.end	= IO_SPACE_LIMIT,
	.flags	= IORESOURCE_IO,
};
EXPORT_SYMBOL(ioport_resource);

struct resource iomem_resource = {
	.name	= "PCI mem",
	.start	= 0,
	.end	= -1,
	.flags	= IORESOURCE_MEM,
};
EXPORT_SYMBOL(iomem_resource);

static int r_show(struct seq_file *m, void *v)
{
	struct resource *root = PDE_DATA(file_inode(m->file));
	struct resource *r = v, *p;
	unsigned long long start, end;
	int width = root->end < 0x10000 ? 4 : 8;
	int depth;

   /*计算子节点的缩进量*/
	for (depth = 0, p = r; depth < MAX_IORES_LEVEL; depth++, p = p->parent)
		if (p->parent == root)
			break;

	/* 权限检查，如果不是超级用户，那么看到的起始和结束物理地址都是0  */
	if (file_ns_capable(m->file, &init_user_ns, CAP_SYS_ADMIN)) {
		start = r->start;
		end = r->end;
	} else {
		start = end = 0;
	}

	seq_printf(m, "%*s%0*llx-%0*llx : %s\n",
			depth * 2, "",
			width, start,
			width, end,
			r->name ? r->name : "");
	return 0;
}

static int __init ioresources_init(void)
{
	proc_create_seq_data("ioports", 0, NULL, &resource_op,
			&ioport_resource);
	proc_create_seq_data("iomem", 0, NULL, &resource_op, &iomem_resource);
	return 0;
}
__initcall(ioresources_init);

/*这个每种CPU架构可以实现自己的meminfo函数，对于x86实现的meminfo函数如下：
void arch_report_meminfo(struct seq_file *m)
{
	seq_printf(m, "DirectMap4k:    %8lu kB\n",
			direct_pages_count[PG_LEVEL_4K] << 2);
#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
	seq_printf(m, "DirectMap2M:    %8lu kB\n",
			direct_pages_count[PG_LEVEL_2M] << 11);
#else
	seq_printf(m, "DirectMap4M:    %8lu kB\n",
			direct_pages_count[PG_LEVEL_2M] << 12);
#endif
	if (direct_gbpages)
		seq_printf(m, "DirectMap1G:    %8lu kB\n",
			direct_pages_count[PG_LEVEL_1G] << 20);
}
*/
void __attribute__((weak)) arch_report_meminfo(struct seq_file *m)
{
}

static void show_val_kb(struct seq_file *m, const char *s, unsigned long num)
{
	seq_put_decimal_ull_width(m, s, num << (PAGE_SHIFT - 10), 8);
	seq_write(m, " kB\n", 4);
}

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

	si_meminfo(&i);
	si_swapinfo(&i);
	committed = vm_memory_committed();

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

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

	available = si_mem_available();
	sreclaimable = global_node_page_state_pages(NR_SLAB_RECLAIMABLE_B);
	sunreclaim = global_node_page_state_pages(NR_SLAB_UNRECLAIMABLE_B);

	show_val_kb(m, "MemTotal:       ", i.totalram);
	show_val_kb(m, "MemFree:        ", i.freeram);
	show_val_kb(m, "MemAvailable:   ", available);
	show_val_kb(m, "Buffers:        ", i.bufferram);
	show_val_kb(m, "Cached:         ", cached);
	show_val_kb(m, "SwapCached:     ", total_swapcache_pages());
	show_val_kb(m, "Active:         ", pages[LRU_ACTIVE_ANON] +
					   pages[LRU_ACTIVE_FILE]);
	show_val_kb(m, "Inactive:       ", pages[LRU_INACTIVE_ANON] +
					   pages[LRU_INACTIVE_FILE]);
	show_val_kb(m, "Active(anon):   ", pages[LRU_ACTIVE_ANON]);
	show_val_kb(m, "Inactive(anon): ", pages[LRU_INACTIVE_ANON]);
	show_val_kb(m, "Active(file):   ", pages[LRU_ACTIVE_FILE]);
	show_val_kb(m, "Inactive(file): ", pages[LRU_INACTIVE_FILE]);
	show_val_kb(m, "Unevictable:    ", pages[LRU_UNEVICTABLE]);
	show_val_kb(m, "Mlocked:        ", global_zone_page_state(NR_MLOCK));

#ifdef CONFIG_HIGHMEM
	show_val_kb(m, "HighTotal:      ", i.totalhigh);
	show_val_kb(m, "HighFree:       ", i.freehigh);
	show_val_kb(m, "LowTotal:       ", i.totalram - i.totalhigh);
	show_val_kb(m, "LowFree:        ", i.freeram - i.freehigh);
#endif

#ifndef CONFIG_MMU
	show_val_kb(m, "MmapCopy:       ",
		    (unsigned long)atomic_long_read(&mmap_pages_allocated));
#endif

	show_val_kb(m, "SwapTotal:      ", i.totalswap);
	show_val_kb(m, "SwapFree:       ", i.freeswap);
	show_val_kb(m, "Dirty:          ",
		    global_node_page_state(NR_FILE_DIRTY));
	show_val_kb(m, "Writeback:      ",
		    global_node_page_state(NR_WRITEBACK));
	show_val_kb(m, "AnonPages:      ",
		    global_node_page_state(NR_ANON_MAPPED));
	show_val_kb(m, "Mapped:         ",
		    global_node_page_state(NR_FILE_MAPPED));
	show_val_kb(m, "Shmem:          ", i.sharedram);
	show_val_kb(m, "KReclaimable:   ", sreclaimable +
		    global_node_page_state(NR_KERNEL_MISC_RECLAIMABLE));
	show_val_kb(m, "Slab:           ", sreclaimable + sunreclaim);
	show_val_kb(m, "SReclaimable:   ", sreclaimable);
	show_val_kb(m, "SUnreclaim:     ", sunreclaim);
	seq_printf(m, "KernelStack:    %8lu kB\n",
		   global_node_page_state(NR_KERNEL_STACK_KB));
#ifdef CONFIG_SHADOW_CALL_STACK
	seq_printf(m, "ShadowCallStack:%8lu kB\n",
		   global_node_page_state(NR_KERNEL_SCS_KB));
#endif
	show_val_kb(m, "PageTables:     ",
		    global_node_page_state(NR_PAGETABLE));

	show_val_kb(m, "NFS_Unstable:   ", 0);
	show_val_kb(m, "Bounce:         ",
		    global_zone_page_state(NR_BOUNCE));
	show_val_kb(m, "WritebackTmp:   ",
		    global_node_page_state(NR_WRITEBACK_TEMP));
	show_val_kb(m, "CommitLimit:    ", vm_commit_limit());
	show_val_kb(m, "Committed_AS:   ", committed);
	seq_printf(m, "VmallocTotal:   %8lu kB\n",
		   (unsigned long)VMALLOC_TOTAL >> 10);
	show_val_kb(m, "VmallocUsed:    ", vmalloc_nr_pages());
	show_val_kb(m, "VmallocChunk:   ", 0ul);
	show_val_kb(m, "Percpu:         ", pcpu_nr_pages());

#ifdef CONFIG_MEMORY_FAILURE
	seq_printf(m, "HardwareCorrupted: %5lu kB\n",
		   atomic_long_read(&num_poisoned_pages) << (PAGE_SHIFT - 10));
#endif

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	show_val_kb(m, "AnonHugePages:  ",
		    global_node_page_state(NR_ANON_THPS));
	show_val_kb(m, "ShmemHugePages: ",
		    global_node_page_state(NR_SHMEM_THPS));
	show_val_kb(m, "ShmemPmdMapped: ",
		    global_node_page_state(NR_SHMEM_PMDMAPPED));
	show_val_kb(m, "FileHugePages:  ",
		    global_node_page_state(NR_FILE_THPS));
	show_val_kb(m, "FilePmdMapped:  ",
		    global_node_page_state(NR_FILE_PMDMAPPED));
#endif

#ifdef CONFIG_CMA
	show_val_kb(m, "CmaTotal:       ", totalcma_pages);
	show_val_kb(m, "CmaFree:        ",
		    global_zone_page_state(NR_FREE_CMA_PAGES));
#endif

	hugetlb_report_meminfo(m);

	arch_report_meminfo(m);

	return 0;
}

static int __init proc_meminfo_init(void)
{
	proc_create_single("meminfo", 0, NULL, meminfo_proc_show);
	return 0;
}
fs_initcall(proc_meminfo_init);

void __init init_mm_internals(void)
{
	...
	proc_create_seq("vmstat", 0444, NULL, &vmstat_op);
	...
}

static int swap_show(struct seq_file *swap, void *v)
{
	struct swap_info_struct *si = v;
	struct file *file;
	int len;
	unsigned int bytes, inuse;

	if (si == SEQ_START_TOKEN) {
		seq_puts(swap, "Filename\t\t\t\tType\t\tSize\t\tUsed\t\tPriority\n");
		return 0;
	}

	/*交换设备的容量，单位为KB*/
	bytes = si->pages << (PAGE_SHIFT - 10);
	/*交换设备已经使用的空间，单位为KB*/
	inuse = si->inuse_pages << (PAGE_SHIFT - 10);

	file = si->swap_file;
	len = seq_file_path(swap, file, " \t\n\\");
	seq_printf(swap, "%*s%s\t%u\t%s%u\t%s%d\n",
			len < 40 ? 40 - len : 1, " ",
			S_ISBLK(file_inode(file)->i_mode) ?
				"partition" : "file\t",
			bytes, bytes < 10000000 ? "\t" : "",
			inuse, inuse < 10000000 ? "\t" : "",
			si->prio);
	return 0;
}