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, 19 insertions, 0 deletions

diff --git a/scripts/checker-valid.sh b/scripts/checker-valid.sh
new file mode 100755
index 000000000..625a789ed
--- /dev/null
+++ b/scripts/checker-valid.sh
@@ -0,0 +1,19 @@
+#!/bin/sh -eu
+# SPDX-License-Identifier: GPL-2.0
+
+[ ! -x "$(command -v "$1")" ] && exit 1
+
+tmp_file=$(mktemp)
+trap "rm -f $tmp_file" EXIT
+
+cat << EOF >$tmp_file
+static inline int u(const int *q)
+{
+	__typeof_unqual__(*q) v = *q;
+	return v;
+}
+EOF
+
+# sparse happily exits with 0 on error so validate
+# there is none on stderr. Use awk as grep is a pain with sh -e
+$@ $tmp_file 2>&1 | awk -v c=1 '/error/{c=0}END{print c}'