[CIFS] Reduce cifs stack space usage

The two cifs functions that used the most stack according
to "make checkstack" have been changed to use less stack.

Thanks to jra and Shaggy for helpful ideas

Signed-off-by: Steve French <sfrench@us.ibm.com>
cc: jra@samba.org
cc: shaggy@us.ibm.com
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 8a49b2e..e9dcf5e 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1146,7 +1146,7 @@
 	pgoff_t end;
 	pgoff_t index;
  	int range_whole = 0;
-	struct kvec iov[32];
+	struct kvec * iov;
 	int len;
 	int n_iov = 0;
 	pgoff_t next;
@@ -1171,15 +1171,21 @@
 	if((cifs_sb->tcon->ses) && (cifs_sb->tcon->ses->server))
 		if(cifs_sb->tcon->ses->server->secMode &
                           (SECMODE_SIGN_REQUIRED | SECMODE_SIGN_ENABLED))
-			if(!experimEnabled)
+			if(!experimEnabled) 
 				return generic_writepages(mapping, wbc);
 
+	iov = kmalloc(32 * sizeof(struct kvec), GFP_KERNEL);
+	if(iov == NULL)
+		return generic_writepages(mapping, wbc);
+
+
 	/*
 	 * BB: Is this meaningful for a non-block-device file system?
 	 * If it is, we should test it again after we do I/O
 	 */
 	if (wbc->nonblocking && bdi_write_congested(bdi)) {
 		wbc->encountered_congestion = 1;
+		kfree(iov);
 		return 0;
 	}
 
@@ -1345,7 +1351,7 @@
 		mapping->writeback_index = index;
 
 	FreeXid(xid);
-
+	kfree(iov);
 	return rc;
 }