netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 44 insertions, 0 deletions

diff --git a/drivers/base/init.c b/drivers/base/init.c
new file mode 100644
index 000000000..af8014416
--- /dev/null
+++ b/drivers/base/init.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2002-3 Patrick Mochel
+ * Copyright (c) 2002-3 Open Source Development Labs
+ */
+
+#include <linux/device.h>
+#include <linux/init.h>
+#include <linux/memory.h>
+#include <linux/of.h>
+#include <linux/backing-dev.h>
+
+#include "base.h"
+
+/**
+ * driver_init - initialize driver model.
+ *
+ * Call the driver model init functions to initialize their
+ * subsystems. Called early from init/main.c.
+ */
+void __init driver_init(void)
+{
+	/* These are the core pieces */
+	bdi_init(&noop_backing_dev_info);
+	devtmpfs_init();
+	devices_init();
+	buses_init();
+	classes_init();
+	firmware_init();
+	hypervisor_init();
+
+	/* These are also core pieces, but must come after the
+	 * core core pieces.
+	 */
+	faux_bus_init();
+	of_core_init();
+	software_node_init();
+	platform_bus_init();
+	auxiliary_bus_init();
+	memory_dev_init();
+	node_dev_init();
+	cpu_dev_init();
+	container_dev_init();
+}