[PATCH 1/3] devmem: change vread()/vwrite() prototype to return success or error code

[Wu Fengguang <fengguang.wu@intel.com>]

[-- Attachment #1: vwrite-ret.patch --]
[-- Type: text/plain, Size: 9598 bytes --]

Silently ignore all vmalloc area holes in vread()/vwrite(),
and report success (or error code in future) to the caller.

The original intention is to fix a vwrite() related bug, where
it could return 0 which cannot be handled correctly by its caller
write_kmem(). Then KAMEZAWA recommends to change the prototype
to make the semantics clear.

CC: Andi Kleen <andi@firstfloor.org>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Christoph Lameter <cl@linux-foundation.org>
CC: Ingo Molnar <mingo@elte.hu>
CC: Tejun Heo <tj@kernel.org>
CC: Nick Piggin <npiggin@suse.de>
CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 drivers/char/mem.c      |   24 ++++++++--------
 fs/proc/kcore.c         |    5 ++-
 include/linux/vmalloc.h |    6 ++--
 mm/nommu.c              |    8 ++---
 mm/vmalloc.c            |   55 +++++++++++---------------------------
 5 files changed, 40 insertions(+), 58 deletions(-)

--- linux-mm.orig/mm/vmalloc.c	2009-09-16 08:52:12.000000000 +0800
+++ linux-mm/mm/vmalloc.c	2009-09-16 09:24:11.000000000 +0800
@@ -1655,7 +1655,6 @@ EXPORT_SYMBOL(vmalloc_32_user);
 static int aligned_vread(char *buf, char *addr, unsigned long count)
 {
 	struct page *p;
-	int copied = 0;
 
 	while (count) {
 		unsigned long offset, length;
@@ -1685,16 +1684,14 @@ static int aligned_vread(char *buf, char
 
 		addr += length;
 		buf += length;
-		copied += length;
 		count -= length;
 	}
-	return copied;
+	return 0;
 }
 
 static int aligned_vwrite(char *buf, char *addr, unsigned long count)
 {
 	struct page *p;
-	int copied = 0;
 
 	while (count) {
 		unsigned long offset, length;
@@ -1722,10 +1719,9 @@ static int aligned_vwrite(char *buf, cha
 		}
 		addr += length;
 		buf += length;
-		copied += length;
 		count -= length;
 	}
-	return copied;
+	return 0;
 }
 
 /**
@@ -1734,9 +1730,7 @@ static int aligned_vwrite(char *buf, cha
  *	@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.
+ *	Returns 0 on success.
  *
  *	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
@@ -1744,23 +1738,21 @@ static int aligned_vwrite(char *buf, cha
  *	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.
+ *	any information, as /dev/kmem and /dev/kcore.
  *
  */
 
-long vread(char *buf, char *addr, unsigned long count)
+int vread(char *buf, char *addr, unsigned long count)
 {
 	struct vm_struct *tmp;
-	char *vaddr, *buf_start = buf;
-	unsigned long buflen = count;
+	char *vaddr;
+	char *buf_end = buf + count;
 	unsigned long n;
 
 	/* Don't allow overflow */
@@ -1794,13 +1786,11 @@ long vread(char *buf, char *addr, unsign
 finished:
 	read_unlock(&vmlist_lock);
 
-	if (buf == buf_start)
-		return 0;
 	/* zero-fill memory holes */
-	if (buf != buf_start + buflen)
-		memset(buf, 0, buflen - (buf - buf_start));
+	if (buf != buf_end)
+		memset(buf, 0, buf_end - buf);
 
-	return buflen;
+	return 0;
 }
 
 /**
@@ -1809,10 +1799,7 @@ finished:
  *	@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.
+ *	Returns 0 on success.
  *
  *	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
@@ -1820,30 +1807,24 @@ finished:
  *	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.
+ *	any information, as /dev/kmem.
  */
 
-long vwrite(char *buf, char *addr, unsigned long count)
+int vwrite(char *buf, char *addr, unsigned long count)
 {
 	struct vm_struct *tmp;
 	char *vaddr;
-	unsigned long n, buflen;
-	int copied = 0;
+	unsigned long n;
 
 	/* Don't allow overflow */
 	if ((unsigned long) addr + count < count)
 		count = -(unsigned long) addr;
-	buflen = count;
 
 	read_lock(&vmlist_lock);
 	for (tmp = vmlist; count && tmp; tmp = tmp->next) {
@@ -1860,19 +1841,15 @@ long vwrite(char *buf, char *addr, unsig
 		n = vaddr + tmp->size - PAGE_SIZE - addr;
 		if (n > count)
 			n = count;
-		if (!(tmp->flags & VM_IOREMAP)) {
+		if (!(tmp->flags & VM_IOREMAP))
 			aligned_vwrite(buf, addr, n);
-			copied++;
-		}
 		buf += n;
 		addr += n;
 		count -= n;
 	}
 finished:
 	read_unlock(&vmlist_lock);
-	if (!copied)
-		return 0;
-	return buflen;
+	return 0;
 }
 
 /**
--- linux-mm.orig/include/linux/vmalloc.h	2009-09-16 08:52:12.000000000 +0800
+++ linux-mm/include/linux/vmalloc.h	2009-09-16 08:52:17.000000000 +0800
@@ -104,9 +104,9 @@ extern void unmap_kernel_range(unsigned 
 extern struct vm_struct *alloc_vm_area(size_t size);
 extern void free_vm_area(struct vm_struct *area);
 
-/* for /dev/kmem */
-extern long vread(char *buf, char *addr, unsigned long count);
-extern long vwrite(char *buf, char *addr, unsigned long count);
+/* for /dev/kmem and /dev/kcore */
+extern int vread(char *buf, char *addr, unsigned long count);
+extern int vwrite(char *buf, char *addr, unsigned long count);
 
 /*
  *	Internals.  Dont't use..
--- linux-mm.orig/drivers/char/mem.c	2009-09-16 08:52:12.000000000 +0800
+++ linux-mm/drivers/char/mem.c	2009-09-16 09:23:00.000000000 +0800
@@ -396,6 +396,7 @@ static ssize_t read_kmem(struct file *fi
 	unsigned long p = *ppos;
 	ssize_t low_count, read, sz;
 	char * kbuf; /* k-addr because vread() takes vmlist_lock rwlock */
+	int err = 0;
 
 	read = 0;
 	if (p < (unsigned long) high_memory) {
@@ -442,12 +443,12 @@ static ssize_t read_kmem(struct file *fi
 			return -ENOMEM;
 		while (count > 0) {
 			sz = size_inside_page(p, count);
-			sz = vread(kbuf, (char *)p, sz);
-			if (!sz)
+			err = vread(kbuf, (char *)p, sz);
+			if (err)
 				break;
 			if (copy_to_user(buf, kbuf, sz)) {
-				free_page((unsigned long)kbuf);
-				return -EFAULT;
+				err = -EFAULT;
+				break;
 			}
 			count -= sz;
 			buf += sz;
@@ -457,7 +458,7 @@ static ssize_t read_kmem(struct file *fi
 		free_page((unsigned long)kbuf);
 	}
  	*ppos = p;
- 	return read;
+	return read ? read : err;
 }
 
 
@@ -521,6 +522,7 @@ static ssize_t write_kmem(struct file * 
 	ssize_t wrote = 0;
 	ssize_t virtr = 0;
 	char * kbuf; /* k-addr because vwrite() takes vmlist_lock rwlock */
+	int err = 0;
 
 	if (p < (unsigned long) high_memory) {
 		unsigned long to_write = min_t(unsigned long, count,
@@ -543,12 +545,12 @@ static ssize_t write_kmem(struct file * 
 
 			n = copy_from_user(kbuf, buf, sz);
 			if (n) {
-				if (wrote + virtr)
-					break;
-				free_page((unsigned long)kbuf);
-				return -EFAULT;
+				err = -EFAULT;
+				break;
 			}
-			sz = vwrite(kbuf, (char *)p, sz);
+			err = vwrite(kbuf, (char *)p, sz);
+			if (err)
+				break;
 			count -= sz;
 			buf += sz;
 			virtr += sz;
@@ -558,7 +560,7 @@ static ssize_t write_kmem(struct file * 
 	}
 
  	*ppos = p;
- 	return virtr + wrote;
+	return virtr + wrote ? : err;
 }
 #endif
 
--- linux-mm.orig/fs/proc/kcore.c	2009-09-16 08:52:12.000000000 +0800
+++ linux-mm/fs/proc/kcore.c	2009-09-16 08:52:17.000000000 +0800
@@ -492,11 +492,14 @@ read_kcore(struct file *file, char __use
 				return -EFAULT;
 		} else if (is_vmalloc_or_module_addr((void *)start)) {
 			char * elf_buf;
+			int err;
 
 			elf_buf = kzalloc(tsz, GFP_KERNEL);
 			if (!elf_buf)
 				return -ENOMEM;
-			vread(elf_buf, (char *)start, tsz);
+			err = vread(elf_buf, (char *)start, tsz);
+			if (err)
+				return err;
 			/* we have to zero-fill user buffer even if no read */
 			if (copy_to_user(buffer, elf_buf, tsz)) {
 				kfree(elf_buf);
--- linux-mm.orig/mm/nommu.c	2009-09-16 09:01:36.000000000 +0800
+++ linux-mm/mm/nommu.c	2009-09-16 09:02:02.000000000 +0800
@@ -263,20 +263,20 @@ unsigned long vmalloc_to_pfn(const void 
 }
 EXPORT_SYMBOL(vmalloc_to_pfn);
 
-long vread(char *buf, char *addr, unsigned long count)
+int vread(char *buf, char *addr, unsigned long count)
 {
 	memcpy(buf, addr, count);
-	return count;
+	return 0;
 }
 
-long vwrite(char *buf, char *addr, unsigned long count)
+int vwrite(char *buf, char *addr, unsigned long count)
 {
 	/* Don't allow overflow */
 	if ((unsigned long) addr + count < count)
 		count = -(unsigned long) addr;
 
 	memcpy(addr, buf, count);
-	return(count);
+	return 0;
 }
 
 /*

--