cifs: allocate kvec array for cifs_readdata as a separate allocation

Eventually, we're going to want to append a list of pages to
cifs_readdata instead of a list of kvecs. To prepare for that, turn
the kvec array allocation into a separate one and just keep a
pointer to it in the readdata.
Signed-off-by: Jeff Layton <jlayton@redhat.com>

fs/cifs/cifsglob.h

@@ -982,7 +982,7 @@ struct cifs_readdata {
 	int (*marshal_iov) (struct cifs_readdata *rdata,
 			    unsigned int remaining);
 	unsigned int			nr_iov;
-	struct kvec			iov[1];
+	struct kvec			*iov;
 };
 
 struct cifs_writedata;

fs/cifs/file.c

@@ -2410,19 +2410,27 @@ ssize_t cifs_strict_writev(struct kiocb *iocb, const struct iovec *iov,
 }
 
 static struct cifs_readdata *
-cifs_readdata_alloc(unsigned int nr_vecs, work_func_t complete)
+cifs_readdata_alloc(unsigned int nr_pages, work_func_t complete)
 {
 	struct cifs_readdata *rdata;
+	struct kvec *iov;
 
-	rdata = kzalloc(sizeof(*rdata) +
-			sizeof(struct kvec) * nr_vecs, GFP_KERNEL);
+	iov = kzalloc(sizeof(*iov) * (nr_pages + 1), GFP_KERNEL);
+	if (!iov)
+		return (struct cifs_readdata *)iov;
+
+	rdata = kzalloc(sizeof(*rdata), GFP_KERNEL);
 	if (rdata != NULL) {
 		kref_init(&rdata->refcount);
 		INIT_LIST_HEAD(&rdata->list);
 		init_completion(&rdata->done);
 		INIT_WORK(&rdata->work, complete);
 		INIT_LIST_HEAD(&rdata->pages);
+		rdata->iov = iov;
+	} else {
+		kfree(iov);
 	}
+
 	return rdata;
 }
 
@@ -2435,6 +2443,7 @@ cifs_readdata_release(struct kref *refcount)
 	if (rdata->cfile)
 		cifsFileInfo_put(rdata->cfile);
 
+	kfree(rdata->iov);
 	kfree(rdata);
 }