ceph: align data in pages in ceph_sync_write

Encrypted files will need to be dealt with in block-sized chunks and
once we do that, the way that ceph_sync_write aligns the data in the
bounce buffer won't be acceptable.

Change it to align the data the same way it would be aligned in the
pagecache.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Reviewed-and-tested-by: Luís Henriques <lhenriques@suse.de>
Reviewed-by: Milind Changire <mchangir@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

Author: jtlayton

fs/ceph/file.c

@@ -1582,6 +1582,7 @@ ceph_sync_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos,
 	bool check_caps = false;
 	struct timespec64 mtime = current_time(inode);
 	size_t count = iov_iter_count(from);
+	size_t off;
 
 	if (ceph_snap(file_inode(file)) != CEPH_NOSNAP)
 		return -EROFS;
@@ -1619,22 +1620,20 @@ ceph_sync_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos,
 			break;
 		}
 
-		/*
-		 * write from beginning of first page,
-		 * regardless of io alignment
-		 */
-		num_pages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
-
+		num_pages = calc_pages_for(pos, len);
 		pages = ceph_alloc_page_vector(num_pages, GFP_KERNEL);
 		if (IS_ERR(pages)) {
 			ret = PTR_ERR(pages);
 			goto out;
 		}
 
 		left = len;
+		off = offset_in_page(pos);
 		for (n = 0; n < num_pages; n++) {
-			size_t plen = min_t(size_t, left, PAGE_SIZE);
-			ret = copy_page_from_iter(pages[n], 0, plen, from);
+			size_t plen = min_t(size_t, left, PAGE_SIZE - off);
+
+			ret = copy_page_from_iter(pages[n], off, plen, from);
+			off = 0;
 			if (ret != plen) {
 				ret = -EFAULT;
 				break;
@@ -1649,8 +1648,9 @@ ceph_sync_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos,
 
 		req->r_inode = inode;
 
-		osd_req_op_extent_osd_data_pages(req, 0, pages, len, 0,
-						false, true);
+		osd_req_op_extent_osd_data_pages(req, 0, pages, len,
+						 offset_in_page(pos),
+						 false, true);
 
 		req->r_mtime = mtime;
 		ceph_osdc_start_request(&fsc->client->osdc, req);