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, 26 insertions, 0 deletions

diff --git a/drivers/firewire/nosy-user.h b/drivers/firewire/nosy-user.h
new file mode 100644
index 000000000..3446c5b77
--- /dev/null
+++ b/drivers/firewire/nosy-user.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __nosy_user_h
+#define __nosy_user_h
+
+#include <linux/ioctl.h>
+#include <linux/types.h>
+
+#define NOSY_IOC_GET_STATS _IOR('&', 0, struct nosy_stats)
+#define NOSY_IOC_START     _IO('&', 1)
+#define NOSY_IOC_STOP      _IO('&', 2)
+#define NOSY_IOC_FILTER    _IOW('&', 2, __u32)
+
+struct nosy_stats {
+	__u32 total_packet_count;
+	__u32 lost_packet_count;
+};
+
+/*
+ * Format of packets returned from the kernel driver:
+ *
+ *	quadlet with timestamp		(microseconds, CPU endian)
+ *	quadlet-padded packet data...	(little endian)
+ *	quadlet with ack		(little endian)
+ */
+
+#endif /* __nosy_user_h */