CIFS: Add support for direct pages in wdata

Add a function to allocate wdata without allocating pages for data
transfer. This gives the caller an option to pass a number of pages that
point to the data buffer to write to.

wdata is reponsible for free those pages after it's done.
Signed-off-by: Long Li <longli@microsoft.com>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/cifsglob.h

@@ -1211,7 +1211,7 @@ struct cifs_writedata {
 	unsigned int			tailsz;
 	unsigned int			credits;
 	unsigned int			nr_pages;
-	struct page			*pages[];
+	struct page			**pages;
 };
 
 /*

fs/cifs/cifsproto.h

@@ -533,6 +533,8 @@ int cifs_async_writev(struct cifs_writedata *wdata,
 void cifs_writev_complete(struct work_struct *work);
 struct cifs_writedata *cifs_writedata_alloc(unsigned int nr_pages,
 						work_func_t complete);
+struct cifs_writedata *cifs_writedata_direct_alloc(struct page **pages,
+						work_func_t complete);
 void cifs_writedata_release(struct kref *refcount);
 int cifs_query_mf_symlink(unsigned int xid, struct cifs_tcon *tcon,
 			  struct cifs_sb_info *cifs_sb,

fs/cifs/cifssmb.c

@@ -1952,6 +1952,7 @@ cifs_writedata_release(struct kref *refcount)
 	if (wdata->cfile)
 		cifsFileInfo_put(wdata->cfile);
 
+	kvfree(wdata->pages);
 	kfree(wdata);
 }
 
@@ -2074,13 +2075,23 @@ cifs_writev_complete(struct work_struct *work)
 
 struct cifs_writedata *
 cifs_writedata_alloc(unsigned int nr_pages, work_func_t complete)
+{
+	struct page **pages =
+		kzalloc(sizeof(struct page *) * nr_pages, GFP_NOFS);
+	if (pages)
+		return cifs_writedata_direct_alloc(pages, complete);
+
+	return NULL;
+}
+
+struct cifs_writedata *
+cifs_writedata_direct_alloc(struct page **pages, work_func_t complete)
 {
 	struct cifs_writedata *wdata;
 
-	/* writedata + number of page pointers */
-	wdata = kzalloc(sizeof(*wdata) +
-			sizeof(struct page *) * nr_pages, GFP_NOFS);
+	wdata = kzalloc(sizeof(*wdata), GFP_NOFS);
 	if (wdata != NULL) {
+		wdata->pages = pages;
 		kref_init(&wdata->refcount);
 		INIT_LIST_HEAD(&wdata->list);
 		init_completion(&wdata->done);