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, 66 insertions, 0 deletions

diff --git a/drivers/gpu/Makefile b/drivers/gpu/Makefile
new file mode 100644
index 000000000..e372fc021
--- /dev/null
+++ b/drivers/gpu/Makefile
@@ -0,0 +1,66 @@
+# SPDX-License-Identifier: GPL-2.0-only
+# drm/tegra depends on host1x, so if both drivers are built-in care must be
+# taken to initialize them in the correct order. Link order is the only way
+# to ensure this currently.
+# Similarly, buddy must come first since it is used by other drivers.
+obj-$(CONFIG_GPU_BUDDY)	+= buddy.o
+obj-y			+= host1x/ drm/ vga/ tests/
+obj-$(CONFIG_IMX_IPUV3_CORE)	+= ipu-v3/
+obj-$(CONFIG_TRACE_GPU_MEM)		+= trace/
+
+# nova-core and nova-drm are built from this Makefile so nova-drm's dependency
+# on nova-core can be expressed as a plain Make prerequisite rather than a
+# recursive sub-make. This is a temporary workaround until the Rust build
+# system supports cross-crate dependencies natively.
+
+obj-$(CONFIG_NOVA_CORE) += nova-core.o
+nova-core-y := nova-core/nova_core.o nova-core/nova_core_exports.o
+
+obj-$(CONFIG_DRM_NOVA) += nova-drm.o
+nova-drm-y := drm/nova/nova.o
+
+# Export Rust symbols from nova-core only if nova-drm actually references them.
+nova-core-export-deps := $(if $(CONFIG_DRM_NOVA),$(obj)/drm/nova/nova.o)
+
+rust_needed_exports = \
+	{ $(if $(strip $(2)),$(NM) -u $(2);,) echo "__DEFINED_RUST_SYMBOLS__"; \
+	  $(NM) -p --defined-only $(1); } | \
+	awk -v fmt='$(3)' ' \
+		/^__DEFINED_RUST_SYMBOLS__$$/ { defs = 1; next } \
+		!defs { if ($$NF ~ /^_R/) needed[$$NF] = 1; next } \
+		defs && $$2 ~ /(T|R|D|B)/ && $$3 ~ /^_R/ && \
+			$$3 !~ /_(init|cleanup)_module$$/ && \
+			$$3 !~ /__(pfx|cfi|odr_asan)/ && \
+			$$3 in needed { printf fmt, $$3 } \
+	'
+
+quiet_cmd_exports = EXPORTS $@
+      cmd_exports = \
+	$(call rust_needed_exports,$<,$(nova-core-export-deps),EXPORT_SYMBOL_RUST_GPL(%s);\n) > $@
+
+$(obj)/nova-core/exports_nova_core_generated.h: $(obj)/nova-core/nova_core.o $(nova-core-export-deps) FORCE
+	$(call if_changed,exports)
+
+targets += nova-core/exports_nova_core_generated.h
+
+$(obj)/nova-core/nova_core_exports.o: $(obj)/nova-core/exports_nova_core_generated.h
+CFLAGS_nova-core/nova_core_exports.o := -I $(objtree)/$(obj)/nova-core
+
+ifdef CONFIG_MODVERSIONS
+# The C export shim declares Rust symbols as `extern int`, so reuse its export
+# list but generate symbol CRCs from the Rust object instead of the shim's DWARF.
+$(obj)/nova-core/nova_core_exports.o: private cmd_gensymtypes_c = \
+	$(call getexportsymbols,\1) | \
+	$(objtree)/scripts/gendwarfksyms/gendwarfksyms \
+		$(if $(KBUILD_GENDWARFKSYMS_STABLE), --stable) \
+		$(if $(KBUILD_SYMTYPES), --symtypes $(@:.o=.symtypes),) \
+		$(obj)/nova-core/nova_core.o
+endif
+
+# Output nova-core's crate metadata for use by nova-drm at compile time.
+RUSTFLAGS_nova-core/nova_core.o += \
+	--emit=metadata=$(objtree)/$(obj)/nova-core/libnova_core.rmeta
+
+# Allow nova-drm to import nova-core's types.
+$(obj)/drm/nova/nova.o: $(obj)/nova-core/nova_core.o
+RUSTFLAGS_drm/nova/nova.o := -L $(objtree)/$(obj)/nova-core --extern nova_core