1 files changed, 506 insertions, 55 deletions

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index f8189a4b3e13..69511e663234 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -25,7 +25,7 @@
 #include <linux/rcupdate.h>
 #include <linux/pfn.h>
 #include <linux/kmemleak.h>
-
+#include <linux/highmem.h>
 #include <asm/atomic.h>
 #include <asm/uaccess.h>
 #include <asm/tlbflush.h>
@@ -168,11 +168,9 @@ static int vmap_page_range_noflush(unsigned long start, unsigned long end,
 		next = pgd_addr_end(addr, end);
 		err = vmap_pud_range(pgd, addr, next, prot, pages, &nr);
 		if (err)
-			break;
+			return err;
 	} while (pgd++, addr = next, addr != end);
 
-	if (unlikely(err))
-		return err;
 	return nr;
 }
 
@@ -186,7 +184,7 @@ static int vmap_page_range(unsigned long start, unsigned long end,
 	return ret;
 }
 
-static inline int is_vmalloc_or_module_addr(const void *x)
+int is_vmalloc_or_module_addr(const void *x)
 {
 	/*
 	 * ARM, x86-64 and sparc64 put modules in a special place,
@@ -265,6 +263,7 @@ struct vmap_area {
 static DEFINE_SPINLOCK(vmap_area_lock);
 static struct rb_root vmap_area_root = RB_ROOT;
 static LIST_HEAD(vmap_area_list);
+static unsigned long vmap_area_pcpu_hole;
 
 static struct vmap_area *__find_vmap_area(unsigned long addr)
 {
@@ -431,6 +430,15 @@ static void __free_vmap_area(struct vmap_area *va)
 	RB_CLEAR_NODE(&va->rb_node);
 	list_del_rcu(&va->list);
 
+	/*
+	 * Track the highest possible candidate for pcpu area
+	 * allocation.  Areas outside of vmalloc area can be returned
+	 * here too, consider only end addresses which fall inside
+	 * vmalloc area proper.
+	 */
+	if (va->va_end > VMALLOC_START && va->va_end <= VMALLOC_END)
+		vmap_area_pcpu_hole = max(vmap_area_pcpu_hole, va->va_end);
+
 	call_rcu(&va->rcu_head, rcu_free_va);
 }
 
@@ -1038,6 +1046,9 @@ void __init vmalloc_init(void)
 		va->va_end = va->va_start + tmp->size;
 		__insert_vmap_area(va);
 	}
+
+	vmap_area_pcpu_hole = VMALLOC_END;
+
 	vmap_initialized = true;
 }
 
@@ -1122,13 +1133,34 @@ EXPORT_SYMBOL_GPL(map_vm_area);
 DEFINE_RWLOCK(vmlist_lock);
 struct vm_struct *vmlist;
 
+static void insert_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
+			      unsigned long flags, void *caller)
+{
+	struct vm_struct *tmp, **p;
+
+	vm->flags = flags;
+	vm->addr = (void *)va->va_start;
+	vm->size = va->va_end - va->va_start;
+	vm->caller = caller;
+	va->private = vm;
+	va->flags |= VM_VM_AREA;
+
+	write_lock(&vmlist_lock);
+	for (p = &vmlist; (tmp = *p) != NULL; p = &tmp->next) {
+		if (tmp->addr >= vm->addr)
+			break;
+	}
+	vm->next = *p;
+	*p = vm;
+	write_unlock(&vmlist_lock);
+}
+
 static struct vm_struct *__get_vm_area_node(unsigned long size,
 		unsigned long flags, unsigned long start, unsigned long end,
 		int node, gfp_t gfp_mask, void *caller)
 {
 	static struct vmap_area *va;
 	struct vm_struct *area;
-	struct vm_struct *tmp, **p;
 	unsigned long align = 1;
 
 	BUG_ON(in_interrupt());
@@ -1147,7 +1179,7 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
 	if (unlikely(!size))
 		return NULL;
 
-	area = kmalloc_node(sizeof(*area), gfp_mask & GFP_RECLAIM_MASK, node);
+	area = kzalloc_node(sizeof(*area), gfp_mask & GFP_RECLAIM_MASK, node);
 	if (unlikely(!area))
 		return NULL;
 
@@ -1162,25 +1194,7 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
 		return NULL;
 	}
 
-	area->flags = flags;
-	area->addr = (void *)va->va_start;
-	area->size = size;
-	area->pages = NULL;
-	area->nr_pages = 0;
-	area->phys_addr = 0;
-	area->caller = caller;
-	va->private = area;
-	va->flags |= VM_VM_AREA;
-
-	write_lock(&vmlist_lock);
-	for (p = &vmlist; (tmp = *p) != NULL; p = &tmp->next) {
-		if (tmp->addr >= area->addr)
-			break;
-	}
-	area->next = *p;
-	*p = area;
-	write_unlock(&vmlist_lock);
-
+	insert_vmalloc_vm(area, va, flags, caller);
 	return area;
 }
 
@@ -1256,17 +1270,21 @@ struct vm_struct *remove_vm_area(const void *addr)
 	if (va && va->flags & VM_VM_AREA) {
 		struct vm_struct *vm = va->private;
 		struct vm_struct *tmp, **p;
-
-		vmap_debug_free_range(va->va_start, va->va_end);
-		free_unmap_vmap_area(va);
-		vm->size -= PAGE_SIZE;
-
+		/*
+		 * remove from list and disallow access to this vm_struct
+		 * before unmap. (address range confliction is maintained by
+		 * vmap.)
+		 */
 		write_lock(&vmlist_lock);
 		for (p = &vmlist; (tmp = *p) != vm; p = &tmp->next)
 			;
 		*p = tmp->next;
 		write_unlock(&vmlist_lock);
 
+		vmap_debug_free_range(va->va_start, va->va_end);
+		free_unmap_vmap_area(va);
+		vm->size -= PAGE_SIZE;
+
 		return vm;
 	}
 	return NULL;
@@ -1368,7 +1386,7 @@ void *vmap(struct page **pages, unsigned int count,
 
 	might_sleep();
 
-	if (count > num_physpages)
+	if (count > totalram_pages)
 		return NULL;
 
 	area = get_vm_area_caller((count << PAGE_SHIFT), flags,
@@ -1475,7 +1493,7 @@ static void *__vmalloc_node(unsigned long size, gfp_t gfp_mask, pgprot_t prot,
 	unsigned long real_size = size;
 
 	size = PAGE_ALIGN(size);
-	if (!size || (size >> PAGE_SHIFT) > num_physpages)
+	if (!size || (size >> PAGE_SHIFT) > totalram_pages)
 		return NULL;
 
 	area = __get_vm_area_node(size, VM_ALLOC, VMALLOC_START, VMALLOC_END,
@@ -1625,10 +1643,120 @@ void *vmalloc_32_user(unsigned long size)
 }
 EXPORT_SYMBOL(vmalloc_32_user);
 
+/*
+ * small helper routine , copy contents to buf from addr.
+ * If the page is not present, fill zero.
+ */
+
+static int aligned_vread(char *buf, char *addr, unsigned long count)
+{
+	struct page *p;
+	int copied = 0;
+
+	while (count) {
+		unsigned long offset, length;
+
+		offset = (unsigned long)addr & ~PAGE_MASK;
+		length = PAGE_SIZE - offset;
+		if (length > count)
+			length = count;
+		p = vmalloc_to_page(addr);
+		/*
+		 * To do safe access to this _mapped_ area, we need
+		 * lock. But adding lock here means that we need to add
+		 * overhead of vmalloc()/vfree() calles for this _debug_
+		 * interface, rarely used. Instead of that, we'll use
+		 * kmap() and get small overhead in this access function.
+		 */
+		if (p) {
+			/*
+			 * we can expect USER0 is not used (see vread/vwrite's
+			 * function description)
+			 */
+			void *map = kmap_atomic(p, KM_USER0);
+			memcpy(buf, map + offset, length);
+			kunmap_atomic(map, KM_USER0);
+		} else
+			memset(buf, 0, length);
+
+		addr += length;
+		buf += length;
+		copied += length;
+		count -= length;
+	}
+	return copied;
+}
+
+static int aligned_vwrite(char *buf, char *addr, unsigned long count)
+{
+	struct page *p;
+	int copied = 0;
+
+	while (count) {
+		unsigned long offset, length;
+
+		offset = (unsigned long)addr & ~PAGE_MASK;
+		length = PAGE_SIZE - offset;
+		if (length > count)
+			length = count;
+		p = vmalloc_to_page(addr);
+		/*
+		 * To do safe access to this _mapped_ area, we need
+		 * lock. But adding lock here means that we need to add
+		 * overhead of vmalloc()/vfree() calles for this _debug_
+		 * interface, rarely used. Instead of that, we'll use
+		 * kmap() and get small overhead in this access function.
+		 */
+		if (p) {
+			/*
+			 * we can expect USER0 is not used (see vread/vwrite's
+			 * function description)
+			 */
+			void *map = kmap_atomic(p, KM_USER0);
+			memcpy(map + offset, buf, length);
+			kunmap_atomic(map, KM_USER0);
+		}
+		addr += length;
+		buf += length;
+		copied += length;
+		count -= length;
+	}
+	return copied;
+}
+
+/**
+ *	vread() -  read vmalloc area in a safe way.
+ *	@buf:		buffer for reading data
+ *	@addr:		vm address.
+ *	@count:		number of bytes to be read.
+ *
+ *	Returns # of bytes which addr and buf should be increased.
+ *	(same number to @count). Returns 0 if [addr...addr+count) doesn't
+ *	includes any intersect with alive vmalloc area.
+ *
+ *	This function checks that addr is a valid vmalloc'ed area, and
+ *	copy data from that area to a given buffer. If the given memory range
+ *	of [addr...addr+count) includes some valid address, data is copied to
+ *	proper area of @buf. If there are memory holes, they'll be zero-filled.
+ *	IOREMAP area is treated as memory hole and no copy is done.
+ *
+ *	If [addr...addr+count) doesn't includes any intersects with alive
+ *	vm_struct area, returns 0.
+ *	@buf should be kernel's buffer. Because	this function uses KM_USER0,
+ *	the caller should guarantee KM_USER0 is not used.
+ *
+ *	Note: In usual ops, vread() is never necessary because the caller
+ *	should know vmalloc() area is valid and can use memcpy().
+ *	This is for routines which have to access vmalloc area without
+ *	any informaion, as /dev/kmem.
+ *
+ */
+
 long vread(char *buf, char *addr, unsigned long count)
 {
 	struct vm_struct *tmp;
 	char *vaddr, *buf_start = buf;
+	unsigned long buflen = count;
 	unsigned long n;
 
 	/* Don't allow overflow */
@@ -1636,7 +1764,7 @@ long vread(char *buf, char *addr, unsigned long count)
 		count = -(unsigned long) addr;
 
 	read_lock(&vmlist_lock);
-	for (tmp = vmlist; tmp; tmp = tmp->next) {
+	for (tmp = vmlist; count && tmp; tmp = tmp->next) {
 		vaddr = (char *) tmp->addr;
 		if (addr >= vaddr + tmp->size - PAGE_SIZE)
 			continue;
@@ -1649,32 +1777,72 @@ long vread(char *buf, char *addr, unsigned long count)
 			count--;
 		}
 		n = vaddr + tmp->size - PAGE_SIZE - addr;
-		do {
-			if (count == 0)
-				goto finished;
-			*buf = *addr;
-			buf++;
-			addr++;
-			count--;
-		} while (--n > 0);
+		if (n > count)
+			n = count;
+		if (!(tmp->flags & VM_IOREMAP))
+			aligned_vread(buf, addr, n);
+		else /* IOREMAP area is treated as memory hole */
+			memset(buf, 0, n);
+		buf += n;
+		addr += n;
+		count -= n;
 	}
 finished:
 	read_unlock(&vmlist_lock);
-	return buf - buf_start;
+
+	if (buf == buf_start)
+		return 0;
+	/* zero-fill memory holes */
+	if (buf != buf_start + buflen)
+		memset(buf, 0, buflen - (buf - buf_start));
+
+	return buflen;
 }
 
+/**
+ *	vwrite() -  write vmalloc area in a safe way.
+ *	@buf:		buffer for source data
+ *	@addr:		vm address.
+ *	@count:		number of bytes to be read.
+ *
+ *	Returns # of bytes which addr and buf should be incresed.
+ *	(same number to @count).
+ *	If [addr...addr+count) doesn't includes any intersect with valid
+ *	vmalloc area, returns 0.
+ *
+ *	This function checks that addr is a valid vmalloc'ed area, and
+ *	copy data from a buffer to the given addr. If specified range of
+ *	[addr...addr+count) includes some valid address, data is copied from
+ *	proper area of @buf. If there are memory holes, no copy to hole.
+ *	IOREMAP area is treated as memory hole and no copy is done.
+ *
+ *	If [addr...addr+count) doesn't includes any intersects with alive
+ *	vm_struct area, returns 0.
+ *	@buf should be kernel's buffer. Because	this function uses KM_USER0,
+ *	the caller should guarantee KM_USER0 is not used.
+ *
+ *	Note: In usual ops, vwrite() is never necessary because the caller
+ *	should know vmalloc() area is valid and can use memcpy().
+ *	This is for routines which have to access vmalloc area without
+ *	any informaion, as /dev/kmem.
+ *
+ *	The caller should guarantee KM_USER1 is not used.
+ */
+
 long vwrite(char *buf, char *addr, unsigned long count)
 {
 	struct vm_struct *tmp;
-	char *vaddr, *buf_start = buf;
-	unsigned long n;
+	char *vaddr;
+	unsigned long n, buflen;
+	int copied = 0;
 
 	/* Don't allow overflow */
 	if ((unsigned long) addr + count < count)
 		count = -(unsigned long) addr;
+	buflen = count;
 
 	read_lock(&vmlist_lock);
-	for (tmp = vmlist; tmp; tmp = tmp->next) {
+	for (tmp = vmlist; count && tmp; tmp = tmp->next) {
 		vaddr = (char *) tmp->addr;
 		if (addr >= vaddr + tmp->size - PAGE_SIZE)
 			continue;
@@ -1686,18 +1854,21 @@ long vwrite(char *buf, char *addr, unsigned long count)
 			count--;
 		}
 		n = vaddr + tmp->size - PAGE_SIZE - addr;
-		do {
-			if (count == 0)
-				goto finished;
-			*addr = *buf;
-			buf++;
-			addr++;
-			count--;
-		} while (--n > 0);
+		if (n > count)
+			n = count;
+		if (!(tmp->flags & VM_IOREMAP)) {
+			aligned_vwrite(buf, addr, n);
+			copied++;
+		}
+		buf += n;
+		addr += n;
+		count -= n;
 	}
 finished:
 	read_unlock(&vmlist_lock);
-	return buf - buf_start;
+	if (!copied)
+		return 0;
+	return buflen;
 }
 
 /**
@@ -1818,6 +1989,286 @@ void free_vm_area(struct vm_struct *area)
 }
 EXPORT_SYMBOL_GPL(free_vm_area);
 
+static struct vmap_area *node_to_va(struct rb_node *n)
+{
+	return n ? rb_entry(n, struct vmap_area, rb_node) : NULL;
+}
+
+/**
+ * pvm_find_next_prev - find the next and prev vmap_area surrounding @end
+ * @end: target address
+ * @pnext: out arg for the next vmap_area
+ * @pprev: out arg for the previous vmap_area
+ *
+ * Returns: %true if either or both of next and prev are found,
+ *	    %false if no vmap_area exists
+ *
+ * Find vmap_areas end addresses of which enclose @end.  ie. if not
+ * NULL, *pnext->va_end > @end and *pprev->va_end <= @end.
+ */
+static bool pvm_find_next_prev(unsigned long end,
+			       struct vmap_area **pnext,
+			       struct vmap_area **pprev)
+{
+	struct rb_node *n = vmap_area_root.rb_node;
+	struct vmap_area *va = NULL;
+
+	while (n) {
+		va = rb_entry(n, struct vmap_area, rb_node);
+		if (end < va->va_end)
+			n = n->rb_left;
+		else if (end > va->va_end)
+			n = n->rb_right;
+		else
+			break;
+	}
+
+	if (!va)
+		return false;
+
+	if (va->va_end > end) {
+		*pnext = va;
+		*pprev = node_to_va(rb_prev(&(*pnext)->rb_node));
+	} else {
+		*pprev = va;
+		*pnext = node_to_va(rb_next(&(*pprev)->rb_node));
+	}
+	return true;
+}
+
+/**
+ * pvm_determine_end - find the highest aligned address between two vmap_areas
+ * @pnext: in/out arg for the next vmap_area
+ * @pprev: in/out arg for the previous vmap_area
+ * @align: alignment
+ *
+ * Returns: determined end address
+ *
+ * Find the highest aligned address between *@pnext and *@pprev below
+ * VMALLOC_END.  *@pnext and *@pprev are adjusted so that the aligned
+ * down address is between the end addresses of the two vmap_areas.
+ *
+ * Please note that the address returned by this function may fall
+ * inside *@pnext vmap_area.  The caller is responsible for checking
+ * that.
+ */
+static unsigned long pvm_determine_end(struct vmap_area **pnext,
+				       struct vmap_area **pprev,
+				       unsigned long align)
+{
+	const unsigned long vmalloc_end = VMALLOC_END & ~(align - 1);
+	unsigned long addr;
+
+	if (*pnext)
+		addr = min((*pnext)->va_start & ~(align - 1), vmalloc_end);
+	else
+		addr = vmalloc_end;
+
+	while (*pprev && (*pprev)->va_end > addr) {
+		*pnext = *pprev;
+		*pprev = node_to_va(rb_prev(&(*pnext)->rb_node));
+	}
+
+	return addr;
+}
+
+/**
+ * pcpu_get_vm_areas - allocate vmalloc areas for percpu allocator
+ * @offsets: array containing offset of each area
+ * @sizes: array containing size of each area
+ * @nr_vms: the number of areas to allocate
+ * @align: alignment, all entries in @offsets and @sizes must be aligned to this
+ * @gfp_mask: allocation mask
+ *
+ * Returns: kmalloc'd vm_struct pointer array pointing to allocated
+ *	    vm_structs on success, %NULL on failure
+ *
+ * Percpu allocator wants to use congruent vm areas so that it can
+ * maintain the offsets among percpu areas.  This function allocates
+ * congruent vmalloc areas for it.  These areas tend to be scattered
+ * pretty far, distance between two areas easily going up to
+ * gigabytes.  To avoid interacting with regular vmallocs, these areas
+ * are allocated from top.
+ *
+ * Despite its complicated look, this allocator is rather simple.  It
+ * does everything top-down and scans areas from the end looking for
+ * matching slot.  While scanning, if any of the areas overlaps with
+ * existing vmap_area, the base address is pulled down to fit the
+ * area.  Scanning is repeated till all the areas fit and then all
+ * necessary data structres are inserted and the result is returned.
+ */
+struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
+				     const size_t *sizes, int nr_vms,
+				     size_t align, gfp_t gfp_mask)
+{
+	const unsigned long vmalloc_start = ALIGN(VMALLOC_START, align);
+	const unsigned long vmalloc_end = VMALLOC_END & ~(align - 1);
+	struct vmap_area **vas, *prev, *next;
+	struct vm_struct **vms;
+	int area, area2, last_area, term_area;
+	unsigned long base, start, end, last_end;
+	bool purged = false;
+
+	gfp_mask &= GFP_RECLAIM_MASK;
+
+	/* verify parameters and allocate data structures */
+	BUG_ON(align & ~PAGE_MASK || !is_power_of_2(align));
+	for (last_area = 0, area = 0; area < nr_vms; area++) {
+		start = offsets[area];
+		end = start + sizes[area];
+
+		/* is everything aligned properly? */
+		BUG_ON(!IS_ALIGNED(offsets[area], align));
+		BUG_ON(!IS_ALIGNED(sizes[area], align));
+
+		/* detect the area with the highest address */
+		if (start > offsets[last_area])
+			last_area = area;
+
+		for (area2 = 0; area2 < nr_vms; area2++) {
+			unsigned long start2 = offsets[area2];
+			unsigned long end2 = start2 + sizes[area2];
+
+			if (area2 == area)
+				continue;
+
+			BUG_ON(start2 >= start && start2 < end);
+			BUG_ON(end2 <= end && end2 > start);
+		}
+	}
+	last_end = offsets[last_area] + sizes[last_area];
+
+	if (vmalloc_end - vmalloc_start < last_end) {
+		WARN_ON(true);
+		return NULL;
+	}
+
+	vms = kzalloc(sizeof(vms[0]) * nr_vms, gfp_mask);
+	vas = kzalloc(sizeof(vas[0]) * nr_vms, gfp_mask);
+	if (!vas || !vms)
+		goto err_free;
+
+	for (area = 0; area < nr_vms; area++) {
+		vas[area] = kzalloc(sizeof(struct vmap_area), gfp_mask);
+		vms[area] = kzalloc(sizeof(struct vm_struct), gfp_mask);
+		if (!vas[area] || !vms[area])
+			goto err_free;
+	}
+retry:
+	spin_lock(&vmap_area_lock);
+
+	/* start scanning - we scan from the top, begin with the last area */
+	area = term_area = last_area;
+	start = offsets[area];
+	end = start + sizes[area];
+
+	if (!pvm_find_next_prev(vmap_area_pcpu_hole, &next, &prev)) {
+		base = vmalloc_end - last_end;
+		goto found;
+	}
+	base = pvm_determine_end(&next, &prev, align) - end;
+
+	while (true) {
+		BUG_ON(next && next->va_end <= base + end);
+		BUG_ON(prev && prev->va_end > base + end);
+
+		/*
+		 * base might have underflowed, add last_end before
+		 * comparing.
+		 */
+		if (base + last_end < vmalloc_start + last_end) {
+			spin_unlock(&vmap_area_lock);
+			if (!purged) {
+				purge_vmap_area_lazy();
+				purged = true;
+				goto retry;
+			}
+			goto err_free;
+		}
+
+		/*
+		 * If next overlaps, move base downwards so that it's
+		 * right below next and then recheck.
+		 */
+		if (next && next->va_start < base + end) {
+			base = pvm_determine_end(&next, &prev, align) - end;
+			term_area = area;
+			continue;
+		}
+
+		/*
+		 * If prev overlaps, shift down next and prev and move
+		 * base so that it's right below new next and then
+		 * recheck.
+		 */
+		if (prev && prev->va_end > base + start)  {
+			next = prev;
+			prev = node_to_va(rb_prev(&next->rb_node));
+			base = pvm_determine_end(&next, &prev, align) - end;
+			term_area = area;
+			continue;
+		}
+
+		/*
+		 * This area fits, move on to the previous one.  If
+		 * the previous one is the terminal one, we're done.
+		 */
+		area = (area + nr_vms - 1) % nr_vms;
+		if (area == term_area)
+			break;
+		start = offsets[area];
+		end = start + sizes[area];
+		pvm_find_next_prev(base + end, &next, &prev);
+	}
+found:
+	/* we've found a fitting base, insert all va's */
+	for (area = 0; area < nr_vms; area++) {
+		struct vmap_area *va = vas[area];
+
+		va->va_start = base + offsets[area];
+		va->va_end = va->va_start + sizes[area];
+		__insert_vmap_area(va);
+	}
+
+	vmap_area_pcpu_hole = base + offsets[last_area];
+
+	spin_unlock(&vmap_area_lock);
+
+	/* insert all vm's */
+	for (area = 0; area < nr_vms; area++)
+		insert_vmalloc_vm(vms[area], vas[area], VM_ALLOC,
+				  pcpu_get_vm_areas);
+
+	kfree(vas);
+	return vms;
+
+err_free:
+	for (area = 0; area < nr_vms; area++) {
+		if (vas)
+			kfree(vas[area]);
+		if (vms)
+			kfree(vms[area]);
+	}
+	kfree(vas);
+	kfree(vms);
+	return NULL;
+}
+
+/**
+ * pcpu_free_vm_areas - free vmalloc areas for percpu allocator
+ * @vms: vm_struct pointer array returned by pcpu_get_vm_areas()
+ * @nr_vms: the number of allocated areas
+ *
+ * Free vm_structs and the array allocated by pcpu_get_vm_areas().
+ */
+void pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
+{
+	int i;
+
+	for (i = 0; i < nr_vms; i++)
+		free_vm_area(vms[i]);
+	kfree(vms);
+}
 
 #ifdef CONFIG_PROC_FS
 static void *s_start(struct seq_file *m, loff_t *pos)