CIFS: Add support for direct pages in rdata

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

rdata is still 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

@@ -1185,7 +1185,7 @@ struct cifs_readdata {
 	unsigned int			tailsz;
 	unsigned int			credits;
 	unsigned int			nr_pages;
-	struct page			*pages[];
+	struct page			**pages;
 };
 
 struct cifs_writedata;

fs/cifs/file.c

@@ -2880,13 +2880,13 @@ cifs_strict_writev(struct kiocb *iocb, struct iov_iter *from)
 }
 
 static struct cifs_readdata *
-cifs_readdata_alloc(unsigned int nr_pages, work_func_t complete)
+cifs_readdata_direct_alloc(struct page **pages, work_func_t complete)
 {
 	struct cifs_readdata *rdata;
 
-	rdata = kzalloc(sizeof(*rdata) + (sizeof(struct page *) * nr_pages),
-			GFP_KERNEL);
+	rdata = kzalloc(sizeof(*rdata), GFP_KERNEL);
 	if (rdata != NULL) {
+		rdata->pages = pages;
 		kref_init(&rdata->refcount);
 		INIT_LIST_HEAD(&rdata->list);
 		init_completion(&rdata->done);
@@ -2896,6 +2896,22 @@ cifs_readdata_alloc(unsigned int nr_pages, work_func_t complete)
 	return rdata;
 }
 
+static struct cifs_readdata *
+cifs_readdata_alloc(unsigned int nr_pages, work_func_t complete)
+{
+	struct page **pages =
+		kzalloc(sizeof(struct page *) * nr_pages, GFP_KERNEL);
+	struct cifs_readdata *ret = NULL;
+
+	if (pages) {
+		ret = cifs_readdata_direct_alloc(pages, complete);
+		if (!ret)
+			kfree(pages);
+	}
+
+	return ret;
+}
+
 void
 cifs_readdata_release(struct kref *refcount)
 {
@@ -2910,6 +2926,7 @@ cifs_readdata_release(struct kref *refcount)
 	if (rdata->cfile)
 		cifsFileInfo_put(rdata->cfile);
 
+	kvfree(rdata->pages);
 	kfree(rdata);
 }