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, 42 insertions, 0 deletions

diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
new file mode 100644
index 000000000..59cbb77b3
--- /dev/null
+++ b/Documentation/dev-tools/index.rst
@@ -0,0 +1,42 @@
+================================
+Development tools for the kernel
+================================
+
+This document is a collection of documents about development tools that can
+be used to work on the kernel. For now, the documents have been pulled
+together without any significant effort to integrate them into a coherent
+whole; patches welcome!
+
+A brief overview of testing-specific tools can be found in
+Documentation/dev-tools/testing-overview.rst
+
+Tools that are specific to debugging can be found in
+Documentation/process/debugging/index.rst
+
+.. toctree::
+   :caption: Table of contents
+   :maxdepth: 2
+
+   testing-overview
+   checkpatch
+   clang-format
+   coccinelle
+   context-analysis
+   sparse
+   kcov
+   gcov
+   kasan
+   kmsan
+   ubsan
+   kmemleak
+   kcsan
+   lkmm/index
+   kfence
+   kselftest
+   kunit/index
+   ktap
+   checkuapi
+   gpio-sloppy-logic-analyzer
+   autofdo
+   propeller
+   container