From dd05add7b2b6004c5fa3a1f276f56d8668f86b65 Mon Sep 17 00:00:00 2001
From: Paulo Alcantara <pc@manguebit.org>
Date: Sat, 26 Sep 2026 19:20:30 -0300
Subject: netfs: zero the tail of a short DIO/unbuffered read

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
---
 scripts/cc-version.sh | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100755 scripts/cc-version.sh

(limited to 'scripts/cc-version.sh')

diff --git a/scripts/cc-version.sh b/scripts/cc-version.sh
new file mode 100755
index 000000000..a7e28b6a5
--- /dev/null
+++ b/scripts/cc-version.sh
@@ -0,0 +1,66 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Print the C compiler name and its version in a 5 or 6-digit form.
+# Also, perform the minimum version check.
+
+set -e
+
+# Print the C compiler name and some version components.
+get_c_compiler_info()
+{
+	cat <<- EOF | "$@" -E -P -x c - 2>/dev/null
+	#if defined(__clang__)
+	Clang	__clang_major__  __clang_minor__  __clang_patchlevel__
+	#elif defined(__GNUC__)
+	GCC	__GNUC__  __GNUC_MINOR__  __GNUC_PATCHLEVEL__
+	#else
+	unknown
+	#endif
+	EOF
+}
+
+# Convert the version string x.y.z to a canonical 5 or 6-digit form.
+get_canonical_version()
+{
+	IFS=.
+	set -- $1
+	echo $((10000 * $1 + 100 * $2 + $3))
+}
+
+# $@ instead of $1 because multiple words might be given, e.g. CC="ccache gcc".
+orig_args="$@"
+set -- $(get_c_compiler_info "$@")
+
+name=$1
+
+min_tool_version=$(dirname $0)/min-tool-version.sh
+
+case "$name" in
+GCC)
+	version=$2.$3.$4
+	min_version=$($min_tool_version gcc)
+	;;
+Clang)
+	version=$2.$3.$4
+	min_version=$($min_tool_version llvm)
+	;;
+*)
+	echo "$orig_args: unknown C compiler" >&2
+	exit 1
+	;;
+esac
+
+cversion=$(get_canonical_version $version)
+min_cversion=$(get_canonical_version $min_version)
+
+if [ "$cversion" -lt "$min_cversion" ]; then
+	echo >&2 "***"
+	echo >&2 "*** C compiler is too old."
+	echo >&2 "***   Your $name version:    $version"
+	echo >&2 "***   Minimum $name version: $min_version"
+	echo >&2 "***"
+	exit 1
+fi
+
+echo $name $cversion
-- 
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