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, 52 insertions, 0 deletions

diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug
new file mode 100644
index 000000000..107db997c
--- /dev/null
+++ b/scripts/Makefile.debug
@@ -0,0 +1,52 @@
+DEBUG_CFLAGS	:=
+DEBUG_RUSTFLAGS	:=
+
+debug-flags-y	:= -g
+
+ifdef CONFIG_DEBUG_INFO_SPLIT
+DEBUG_CFLAGS	+= -gsplit-dwarf
+endif
+
+debug-flags-$(CONFIG_DEBUG_INFO_DWARF4)	+= -gdwarf-4
+debug-flags-$(CONFIG_DEBUG_INFO_DWARF5)	+= -gdwarf-5
+ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_AS_IS_GNU),yy)
+# Clang does not pass -g or -gdwarf-* option down to GAS.
+# Add -Wa, prefix to explicitly specify the flags.
+KBUILD_AFLAGS	+= $(addprefix -Wa$(comma), $(debug-flags-y))
+endif
+DEBUG_CFLAGS	+= $(debug-flags-y)
+KBUILD_AFLAGS	+= $(debug-flags-y)
+
+ifdef CONFIG_DEBUG_INFO_DWARF4
+DEBUG_RUSTFLAGS	+= -Zdwarf-version=4
+else ifdef CONFIG_DEBUG_INFO_DWARF5
+DEBUG_RUSTFLAGS	+= -Zdwarf-version=5
+endif
+
+ifdef CONFIG_DEBUG_INFO_REDUCED
+DEBUG_CFLAGS	+= -fno-var-tracking
+DEBUG_RUSTFLAGS	+= -Cdebuginfo=1
+ifdef CONFIG_CC_IS_GCC
+DEBUG_CFLAGS	+= -femit-struct-debug-baseonly
+endif
+else
+DEBUG_RUSTFLAGS	+= -Cdebuginfo=2
+endif
+
+ifdef CONFIG_DEBUG_INFO_COMPRESSED_ZLIB
+DEBUG_CFLAGS	+= -gz=zlib
+DEBUG_RUSTFLAGS	+= -Zdebuginfo-compression=zlib
+KBUILD_AFLAGS	+= -gz=zlib
+KBUILD_LDFLAGS	+= --compress-debug-sections=zlib
+else ifdef CONFIG_DEBUG_INFO_COMPRESSED_ZSTD
+DEBUG_CFLAGS	+= -gz=zstd
+DEBUG_RUSTFLAGS	+= -Zdebuginfo-compression=zstd
+KBUILD_AFLAGS	+= -gz=zstd
+KBUILD_LDFLAGS	+= --compress-debug-sections=zstd
+endif
+
+KBUILD_CFLAGS	+= $(DEBUG_CFLAGS)
+export DEBUG_CFLAGS
+
+KBUILD_RUSTFLAGS += $(DEBUG_RUSTFLAGS)
+export DEBUG_RUSTFLAGS