CIFS: Add copy into pages callback for a read operation

BugLink: http://bugs.launchpad.net/bugs/1670508

Since we have two different types of reads (pagecache and direct)
we need to process such responses differently after decryption of
a packet. The change allows to specify a callback that copies a read
payload data into preallocated pages.
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
(cherry picked from commit d70b9104)
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>

fs/cifs/cifsglob.h

@@ -1121,6 +1121,9 @@ struct cifs_readdata {
 	int (*read_into_pages)(struct TCP_Server_Info *server,
 				struct cifs_readdata *rdata,
 				unsigned int len);
+	int (*copy_into_pages)(struct TCP_Server_Info *server,
+				struct cifs_readdata *rdata,
+				struct iov_iter *iter);
 	struct kvec			iov[2];
 	unsigned int			pagesz;
 	unsigned int			tailsz;

fs/cifs/file.c

@@ -2859,8 +2859,9 @@ cifs_uncached_readv_complete(struct work_struct *work)
 }
 
 static int
-cifs_uncached_read_into_pages(struct TCP_Server_Info *server,
-			struct cifs_readdata *rdata, unsigned int len)
+uncached_fill_pages(struct TCP_Server_Info *server,
+		    struct cifs_readdata *rdata, struct iov_iter *iter,
+		    unsigned int len)
 {
 	int result = 0;
 	unsigned int i;
@@ -2889,7 +2890,10 @@ cifs_uncached_read_into_pages(struct TCP_Server_Info *server,
 			rdata->tailsz = len;
 			len = 0;
 		}
-		result = cifs_read_page_from_socket(server, page, n);
+		if (iter)
+			result = copy_page_from_iter(page, 0, n, iter);
+		else
+			result = cifs_read_page_from_socket(server, page, n);
 		if (result < 0)
 			break;
 
@@ -2900,6 +2904,21 @@ cifs_uncached_read_into_pages(struct TCP_Server_Info *server,
 						rdata->got_bytes : result;
 }
 
+static int
+cifs_uncached_read_into_pages(struct TCP_Server_Info *server,
+			      struct cifs_readdata *rdata, unsigned int len)
+{
+	return uncached_fill_pages(server, rdata, NULL, len);
+}
+
+static int
+cifs_uncached_copy_into_pages(struct TCP_Server_Info *server,
+			      struct cifs_readdata *rdata,
+			      struct iov_iter *iter)
+{
+	return uncached_fill_pages(server, rdata, iter, iter->count);
+}
+
 static int
 cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
 		     struct cifs_sb_info *cifs_sb, struct list_head *rdata_list)
@@ -2947,6 +2966,7 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
 		rdata->pid = pid;
 		rdata->pagesz = PAGE_SIZE;
 		rdata->read_into_pages = cifs_uncached_read_into_pages;
+		rdata->copy_into_pages = cifs_uncached_copy_into_pages;
 		rdata->credits = credits;
 
 		if (!rdata->cfile->invalidHandle ||
@@ -3297,8 +3317,9 @@ cifs_readv_complete(struct work_struct *work)
 }
 
 static int
-cifs_readpages_read_into_pages(struct TCP_Server_Info *server,
-			struct cifs_readdata *rdata, unsigned int len)
+readpages_fill_pages(struct TCP_Server_Info *server,
+		     struct cifs_readdata *rdata, struct iov_iter *iter,
+		     unsigned int len)
 {
 	int result = 0;
 	unsigned int i;
@@ -3352,7 +3373,10 @@ cifs_readpages_read_into_pages(struct TCP_Server_Info *server,
 			continue;
 		}
 
-		result = cifs_read_page_from_socket(server, page, n);
+		if (iter)
+			result = copy_page_from_iter(page, 0, n, iter);
+		else
+			result = cifs_read_page_from_socket(server, page, n);
 		if (result < 0)
 			break;
 
@@ -3363,6 +3387,21 @@ cifs_readpages_read_into_pages(struct TCP_Server_Info *server,
 						rdata->got_bytes : result;
 }
 
+static int
+cifs_readpages_read_into_pages(struct TCP_Server_Info *server,
+			       struct cifs_readdata *rdata, unsigned int len)
+{
+	return readpages_fill_pages(server, rdata, NULL, len);
+}
+
+static int
+cifs_readpages_copy_into_pages(struct TCP_Server_Info *server,
+			       struct cifs_readdata *rdata,
+			       struct iov_iter *iter)
+{
+	return readpages_fill_pages(server, rdata, iter, iter->count);
+}
+
 static int
 readpages_get_pages(struct address_space *mapping, struct list_head *page_list,
 		    unsigned int rsize, struct list_head *tmplist,
@@ -3517,6 +3556,7 @@ static int cifs_readpages(struct file *file, struct address_space *mapping,
 		rdata->pid = pid;
 		rdata->pagesz = PAGE_CACHE_SIZE;
 		rdata->read_into_pages = cifs_readpages_read_into_pages;
+		rdata->copy_into_pages = cifs_readpages_copy_into_pages;
 		rdata->credits = credits;
 
 		list_for_each_entry_safe(page, tpage, &tmplist, lru) {