afs: Don't invoke the server to read data beyond EOF

When writing a new page, clear space in the page rather than attempting to
load it from the server if the space is beyond the EOF.

Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/fs/afs/write.c b/fs/afs/write.c
index 1dfca4b..05e6bc6 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -33,10 +33,21 @@
 			 loff_t pos, unsigned int len, struct page *page)
 {
 	struct afs_read *req;
+	size_t p;
+	void *data;
 	int ret;
 
 	_enter(",,%llu", (unsigned long long)pos);
 
+	if (pos >= vnode->vfs_inode.i_size) {
+		p = pos & ~PAGE_MASK;
+		ASSERTCMP(p + len, <=, PAGE_SIZE);
+		data = kmap(page);
+		memset(data + p, 0, len);
+		kunmap(page);
+		return 0;
+	}
+
 	req = kzalloc(sizeof(struct afs_read), GFP_KERNEL);
 	if (!req)
 		return -ENOMEM;