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/scripts/Makefile.clang b/scripts/Makefile.clang
new file mode 100644
index 000000000..b67636b28
--- /dev/null
+++ b/scripts/Makefile.clang
@@ -0,0 +1,42 @@
+# Individual arch/{arch}/Makefiles should use -EL/-EB to set intended
+# endianness and -m32/-m64 to set word size based on Kconfigs instead of
+# relying on the target triple.
+CLANG_TARGET_FLAGS_arm		:= arm-linux-gnueabi
+CLANG_TARGET_FLAGS_arm64	:= aarch64-linux-gnu
+CLANG_TARGET_FLAGS_hexagon	:= hexagon-linux-musl
+CLANG_TARGET_FLAGS_loongarch	:= loongarch64-linux-gnusf
+CLANG_TARGET_FLAGS_m68k		:= m68k-linux-gnu
+CLANG_TARGET_FLAGS_mips		:= mipsel-linux-gnu
+CLANG_TARGET_FLAGS_powerpc	:= powerpc64le-linux-gnu
+CLANG_TARGET_FLAGS_riscv	:= riscv64-linux-gnu
+CLANG_TARGET_FLAGS_s390		:= s390x-linux-gnu
+CLANG_TARGET_FLAGS_sparc	:= sparc64-linux-gnu
+CLANG_TARGET_FLAGS_x86		:= x86_64-linux-gnu
+# This is only for i386 UM builds, which need the 32-bit target not -m32
+CLANG_TARGET_FLAGS_i386		:= i386-linux-gnu
+CLANG_TARGET_FLAGS_um		:= $(CLANG_TARGET_FLAGS_$(SUBARCH))
+CLANG_TARGET_FLAGS		:= $(CLANG_TARGET_FLAGS_$(SRCARCH))
+
+ifeq ($(CLANG_TARGET_FLAGS),)
+$(error add '--target=' option to scripts/Makefile.clang)
+else
+CLANG_FLAGS	+= --target=$(CLANG_TARGET_FLAGS)
+endif
+
+ifeq ($(LLVM_IAS),0)
+CLANG_FLAGS	+= -fno-integrated-as
+GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
+CLANG_FLAGS	+= --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
+else
+CLANG_FLAGS	+= -fintegrated-as
+endif
+# By default, clang only warns when it encounters an unknown warning flag or
+# certain optimization flags it knows it has not implemented.
+# Make it behave more like gcc by erroring when these flags are encountered
+# so they can be implemented or wrapped in cc-option.
+CLANG_FLAGS	+= -Werror=unknown-warning-option
+CLANG_FLAGS	+= -Werror=ignored-optimization-argument
+CLANG_FLAGS	+= -Werror=option-ignored
+CLANG_FLAGS	+= -Werror=unused-command-line-argument
+KBUILD_CPPFLAGS	+= $(CLANG_FLAGS)
+export CLANG_FLAGS