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, 31 insertions, 0 deletions

diff --git a/include/clocksource/timer-goldfish.h b/include/clocksource/timer-goldfish.h
new file mode 100644
index 000000000..05a3a4f61
--- /dev/null
+++ b/include/clocksource/timer-goldfish.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * goldfish-timer clocksource
+ * Registers definition for the goldfish-timer device
+ */
+
+#ifndef _CLOCKSOURCE_TIMER_GOLDFISH_H
+#define _CLOCKSOURCE_TIMER_GOLDFISH_H
+
+/*
+ * TIMER_TIME_LOW	 get low bits of current time and update TIMER_TIME_HIGH
+ * TIMER_TIME_HIGH	 get high bits of time at last TIMER_TIME_LOW read
+ * TIMER_ALARM_LOW	 set low bits of alarm and activate it
+ * TIMER_ALARM_HIGH	 set high bits of next alarm
+ * TIMER_IRQ_ENABLED	 enable alarm interrupt
+ * TIMER_CLEAR_ALARM	 disarm an existing alarm
+ * TIMER_ALARM_STATUS	 alarm status (running or not)
+ * TIMER_CLEAR_INTERRUPT clear interrupt
+ */
+#define TIMER_TIME_LOW		0x00
+#define TIMER_TIME_HIGH		0x04
+#define TIMER_ALARM_LOW		0x08
+#define TIMER_ALARM_HIGH	0x0c
+#define TIMER_IRQ_ENABLED	0x10
+#define TIMER_CLEAR_ALARM	0x14
+#define TIMER_ALARM_STATUS	0x18
+#define TIMER_CLEAR_INTERRUPT	0x1c
+
+extern int goldfish_timer_init(int irq, void __iomem *base);
+
+#endif /* _CLOCKSOURCE_TIMER_GOLDFISH_H */