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, 32 insertions, 0 deletions

diff --git a/scripts/makelst b/scripts/makelst
new file mode 100755
index 000000000..e432af073
--- /dev/null
+++ b/scripts/makelst
@@ -0,0 +1,32 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# A script to dump mixed source code & assembly
+# with correct relocations from System.map
+# Requires the following lines in makefile:
+#%.lst: %.c
+#	$(CC) $(c_flags) -g -c -o $*.o $< &&
+#	$(srctree)/scripts/makelst $*.o System.map $(OBJDUMP) > $@
+#
+# Copyright (C) 2000 IBM Corporation
+# Author(s): DJ Barrow (djbarrow@de.ibm.com,barrow_dj@yahoo.com)
+#            William Stearns <wstearns@pobox.com>
+#
+
+# awk style field access
+field() {
+  shift $1 ; echo $1
+}
+
+t1=`$3 --syms $1 | grep .text | grep -m1 " F "`
+if [ -n "$t1" ]; then
+  t2=`field 6 $t1`
+  if [ ! -r $2 ]; then
+    echo "No System.map" >&2
+  else
+    t3=`grep $t2 $2`
+    t4=`field 1 $t3`
+    t5=`field 1 $t1`
+    t6=`printf "%lu" $((0x$t4 - 0x$t5))`
+  fi
+fi
+$3 -r --source --adjust-vma=${t6:-0} $1