[PATCH] devmem: handle partial kmem write/read

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

Current vwrite silently ignores vwrite() to vmap holes.
Better behavior should be stop the write and return
on such holes.

Also return on partial read, which may happen in future
(eg. hit hwpoison pages).

CC: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 drivers/char/mem.c |   30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

--- linux-mm.orig/drivers/char/mem.c	2009-09-14 10:59:50.000000000 +0800
+++ linux-mm/drivers/char/mem.c	2009-09-14 11:06:25.000000000 +0800
@@ -444,18 +444,22 @@ static ssize_t read_kmem(struct file *fi
 		if (!kbuf)
 			return -ENOMEM;
 		while (count > 0) {
+			unsigned long n;
+
 			sz = size_inside_page(p, count);
-			sz = vread(kbuf, (char *)p, sz);
-			if (!sz)
+			n = vread(kbuf, (char *)p, sz);
+			if (!n)
 				break;
-			if (copy_to_user(buf, kbuf, sz)) {
+			if (copy_to_user(buf, kbuf, n)) {
 				free_page((unsigned long)kbuf);
 				return -EFAULT;
 			}
-			count -= sz;
-			buf += sz;
-			read += sz;
-			p += sz;
+			count -= n;
+			buf += n;
+			read += n;
+			p += n;
+			if (n < sz)
+				break;
 		}
 		free_page((unsigned long)kbuf);
 	}
@@ -551,11 +555,13 @@ static ssize_t write_kmem(struct file * 
 				free_page((unsigned long)kbuf);
 				return -EFAULT;
 			}
-			sz = vwrite(kbuf, (char *)p, sz);
-			count -= sz;
-			buf += sz;
-			virtr += sz;
-			p += sz;
+			n = vwrite(kbuf, (char *)p, sz);
+			count -= n;
+			buf += n;
+			virtr += n;
+			p += n;
+			if (n < sz)
+				break;
 		}
 		free_page((unsigned long)kbuf);
 	}