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, 27 insertions, 0 deletions

diff --git a/include/net/pptp.h b/include/net/pptp.h
new file mode 100644
index 000000000..e63176bdd
--- /dev/null
+++ b/include/net/pptp.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _NET_PPTP_H
+#define _NET_PPTP_H
+
+#include <linux/types.h>
+#include <net/gre.h>
+
+#define PPP_LCP_ECHOREQ 0x09
+#define PPP_LCP_ECHOREP 0x0A
+#define SC_RCV_BITS     (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
+
+#define MISSING_WINDOW 20
+#define WRAPPED(curseq, lastseq)\
+	((((curseq) & 0xffffff00) == 0) &&\
+	(((lastseq) & 0xffffff00) == 0xffffff00))
+
+#define PPTP_HEADER_OVERHEAD (2+sizeof(struct pptp_gre_header))
+struct pptp_gre_header {
+	struct gre_base_hdr gre_hd;
+	__be16 payload_len;
+	__be16 call_id;
+	__be32 seq;
+	__be32 ack;
+} __packed;
+
+
+#endif