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

2 files changed, 59 insertions, 0 deletions

diff --git a/rust/uapi/lib.rs b/rust/uapi/lib.rs
new file mode 100644
index 000000000..003e6d4f7
--- /dev/null
+++ b/rust/uapi/lib.rs
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! UAPI Bindings.
+//!
+//! Contains the bindings generated by `bindgen` for UAPI interfaces.
+//!
+//! This crate may be used directly by drivers that need to interact with
+//! userspace APIs.
+
+#![no_std]
+#![allow(
+    clippy::all,
+    clippy::as_underscore,
+    clippy::cast_lossless,
+    clippy::ptr_as_ptr,
+    clippy::ref_as_ptr,
+    clippy::undocumented_unsafe_blocks,
+    dead_code,
+    missing_docs,
+    non_camel_case_types,
+    non_upper_case_globals,
+    non_snake_case,
+    improper_ctypes,
+    unreachable_pub,
+    unsafe_op_in_unsafe_fn
+)]
+#![cfg_attr(not(CONFIG_RUSTC_HAS_UNNECESSARY_TRANSMUTES), allow(unknown_lints))]
+#![allow(unnecessary_transmutes)]
+#![cfg_attr(
+    CONFIG_RUSTC_HAS_SUSPICIOUS_RUNTIME_SYMBOL_DEFINITIONS,
+    allow(suspicious_runtime_symbol_definitions)
+)]
+#![feature(cfi_encoding)]
+
+// Manual definition of blocklisted types.
+type __kernel_size_t = usize;
+type __kernel_ssize_t = isize;
+type __kernel_ptrdiff_t = isize;
+
+use pin_init::MaybeZeroable;
+
+include!(concat!(env!("OBJTREE"), "/rust/uapi/uapi_generated.rs"));
diff --git a/rust/uapi/uapi_helper.h b/rust/uapi/uapi_helper.h
new file mode 100644
index 000000000..489748ef6
--- /dev/null
+++ b/rust/uapi/uapi_helper.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Header that contains the headers for which Rust UAPI bindings
+ * will be automatically generated by `bindgen`.
+ *
+ * Sorted alphabetically.
+ */
+
+#include <uapi/drm/drm.h>
+#include <uapi/drm/nova_drm.h>
+#include <uapi/drm/panthor_drm.h>
+#include <uapi/linux/android/binder.h>
+#include <uapi/linux/android/binder_netlink.h>
+#include <uapi/linux/ioctl.h>
+#include <uapi/linux/mdio.h>
+#include <uapi/linux/mii.h>
+#include <uapi/linux/ethtool.h>