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, 60 insertions, 0 deletions

diff --git a/tools/docs/parse-headers.py b/tools/docs/parse-headers.py
new file mode 100755
index 000000000..436acea4c
--- /dev/null
+++ b/tools/docs/parse-headers.py
@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2016, 2025 by Mauro Carvalho Chehab <mchehab@kernel.org>.
+# pylint: disable=C0103
+
+"""
+Convert a C header or source file ``FILE_IN``, into a ReStructured Text
+included via ..parsed-literal block with cross-references for the
+documentation files that describe the API. It accepts an optional
+``FILE_RULES`` file to describes what elements will be either ignored or
+be pointed to a non-default reference type/name.
+
+The output is written at ``FILE_OUT``.
+
+It is capable of identifying defines, functions, structs, typedefs,
+enums and enum symbols and create cross-references for all of them.
+It is also capable of distinguish #define used for specifying a Linux
+ioctl.
+
+The optional ``FILE_RULES`` contains a set of rules like:
+
+    ignore ioctl VIDIOC_ENUM_FMT
+    replace ioctl VIDIOC_DQBUF vidioc_qbuf
+    replace define V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ :c:type:`v4l2_event_motion_det`
+"""
+
+import argparse, sys
+import os.path
+
+src_dir = os.path.dirname(os.path.realpath(__file__))
+sys.path.insert(0, os.path.join(src_dir, '../lib/python'))
+from kdoc.parse_data_structs import ParseDataStructs
+from kdoc.enrich_formatter import EnrichFormatter
+
+def main():
+    """Main function"""
+    parser = argparse.ArgumentParser(description=__doc__,
+                                     formatter_class=EnrichFormatter)
+
+    parser.add_argument("-d", "--debug", action="count", default=0,
+                        help="Increase debug level. Can be used multiple times")
+    parser.add_argument("-t", "--toc", action="store_true",
+                        help="instead of a literal block, outputs a TOC table at the RST file")
+
+    parser.add_argument("file_in", help="Input C file")
+    parser.add_argument("file_out", help="Output RST file")
+    parser.add_argument("file_rules", nargs="?",
+                        help="Exceptions file (optional)")
+
+    args = parser.parse_args()
+
+    parser = ParseDataStructs(debug=args.debug)
+    parser.parse_file(args.file_in, args.file_rules)
+
+    parser.debug_print()
+    parser.write_output(args.file_in, args.file_out, args.toc)
+
+
+if __name__ == "__main__":
+    main()