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, 32 insertions, 0 deletions

diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
new file mode 100644
index 000000000..a1812985a
--- /dev/null
+++ b/scripts/Makefile.btf
@@ -0,0 +1,32 @@
+# SPDX-License-Identifier: GPL-2.0
+
+pahole-ver := $(CONFIG_PAHOLE_VERSION)
+pahole-flags-y :=
+
+JOBS := $(patsubst -j%,%,$(filter -j%,$(MAKEFLAGS)))
+
+ifeq ($(call test-le, $(pahole-ver), 125),y)
+
+pahole-flags-y                                  	+= --btf_gen_floats -j$(JOBS)
+
+pahole-flags-$(call test-ge, $(pahole-ver), 125)	+= --skip_encoding_btf_inconsistent_proto --btf_gen_optimized
+
+else
+
+# Switch to using --btf_features for v1.26 and later.
+pahole-flags-$(call test-ge, $(pahole-ver), 126)  = -j$(JOBS) --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func
+
+pahole-flags-$(call test-ge, $(pahole-ver), 131) += --btf_features=layout
+
+endif
+
+pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE)		+= --lang_exclude=rust
+
+export PAHOLE_FLAGS := $(pahole-flags-y)
+
+resolve-btfids-flags-y :=
+resolve-btfids-flags-$(CONFIG_WERROR) += --fatal_warnings
+resolve-btfids-flags-$(if $(KBUILD_EXTMOD),y) += --distill_base
+resolve-btfids-flags-$(if $(KBUILD_VERBOSE),y) += --verbose
+
+export RESOLVE_BTFIDS_FLAGS := $(resolve-btfids-flags-y)