ceph: fix page alignment corrections

 dd if=/dev/urandom of=/mnt/fs_depot/dd10 bs=500 seek=8388 count=1
 dd if=/mnt/fs_depot/dd10 of=/root/dd10out bs=500 skip=8388 count=1

Reported-by: Henry C Chang <henry.cy.chang@gmail.com>
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/file.c

@@ -290,7 +290,6 @@ static int striped_read(struct inode *inode,
 	struct ceph_inode_info *ci = ceph_inode(inode);
 	u64 pos, this_len;
 	int io_align, page_align;
-	int page_off = off & ~PAGE_CACHE_MASK; /* first byte's offset in page */
 	int left, pages_left;
 	int read;
 	struct page **page_pos;
@@ -326,12 +325,11 @@ static int striped_read(struct inode *inode,
 	     ret, hit_stripe ? " HITSTRIPE" : "", was_short ? " SHORT" : "");
 
 	if (ret > 0) {
-		int didpages =
-			((pos & ~PAGE_CACHE_MASK) + ret) >> PAGE_CACHE_SHIFT;
+		int didpages = (page_align + ret) >> PAGE_CACHE_SHIFT;
 
 		if (read < pos - off) {
 			dout(" zero gap %llu to %llu\n", off + read, pos);
-			ceph_zero_page_vector_range(page_off + read,
+			ceph_zero_page_vector_range(page_align + read,
 						    pos - off - read, pages);
 		}
 		pos += ret;
@@ -356,7 +354,7 @@ static int striped_read(struct inode *inode,
 				left = inode->i_size - pos;
 
 			dout("zero tail %d\n", left);
-			ceph_zero_page_vector_range(page_off + read, left,
+			ceph_zero_page_vector_range(page_align + read, left,
 						    pages);
 			read += left;
 		}