build: add ZFS_DEBUG Kconfig for copy-builtin

... so we can toggle ZFS debug assertions from the
Linux kernel build without having to regenerate the
ZFS patch.

Update the qemu test script to also set this kernel
config.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Timothy Day <timday@thelustrecollective.com>
Co-authored-by: Timothy Day <timday@thelustrecollective.com>
Closes #18595

.github/workflows/scripts/qemu-6-tests.sh

@@ -79,6 +79,7 @@ function do_builtin_build() {
 
   cd $HOME/linux-$fullver
   ./scripts/config --enable ZFS
+  ./scripts/config --enable ZFS_DEBUG
   yes "" | make oldconfig
   make -j `nproc`
   ) &> /var/tmp/builtin.txt || rc=$?

config/zfs-build.m4

@@ -39,6 +39,18 @@ dnl # (If INVARIANTS is detected, we need to force DEBUG, or strange panics
 dnl # can ensue.)
 dnl #
 AC_DEFUN([ZFS_AC_DEBUG], [
+	dnl #
+	dnl # In the Linux kernel copy-builtin build, assertion/debug support
+	dnl # is selected by CONFIG_ZFS_DEBUG (Kconfig).
+	dnl #
+	AH_BOTTOM([
+#ifdef CONFIG_ZFS
+#undef ZFS_DEBUG
+#ifdef CONFIG_ZFS_DEBUG
+#define ZFS_DEBUG 1
+#endif
+#endif])
+
 	AC_MSG_CHECKING([whether assertion support will be enabled])
 	AC_ARG_ENABLE([debug],
 		[AS_HELP_STRING([--enable-debug],

copy-builtin

@@ -43,6 +43,17 @@ config ZFS
 
 	  To compile this file system support as a module, choose M here.
 
+	  If unsure, say N.
+
+config ZFS_DEBUG
+	bool "ZFS debugging"
+	depends on ZFS
+	help
+	  Enable ZFS debugging. This turns on all ASSERT() assertions,
+	  enables additional debug-only code paths, and promotes
+	  compiler warnings to errors. This should only be enabled for
+	  development or troubleshooting.
+
 	  If unsure, say N.
 EOF
 

module/Kbuild.in

@@ -4,9 +4,11 @@
 
 ZFS_MODULE_CFLAGS += -std=gnu11 -Wno-declaration-after-statement
 ZFS_MODULE_CFLAGS += -Wmissing-prototypes
-ZFS_MODULE_CFLAGS += @KERNEL_DEBUG_CFLAGS@ @KERNEL_NO_FORMAT_ZERO_LENGTH@
+ZFS_MODULE_CFLAGS += @KERNEL_NO_FORMAT_ZERO_LENGTH@
 
 ifneq ($(KBUILD_EXTMOD),)
+ZFS_MODULE_CFLAGS += @KERNEL_DEBUG_CFLAGS@
+ZFS_MODULE_CPPFLAGS += @KERNEL_DEBUG_CPPFLAGS@
 zfs_include = @abs_top_srcdir@/include
 icp_include = @abs_srcdir@/icp/include
 zstd_include = @abs_srcdir@/zstd/include
@@ -16,6 +18,12 @@ ZFS_MODULE_CFLAGS += -I@abs_top_builddir@/include
 src = @abs_srcdir@
 obj = @abs_builddir@
 else
+ifeq ($(CONFIG_ZFS_DEBUG),y)
+ZFS_MODULE_CFLAGS += -Werror
+ZFS_MODULE_CPPFLAGS += -DDEBUG -UNDEBUG -DZFS_DEBUG
+else
+ZFS_MODULE_CPPFLAGS += -UDEBUG -DNDEBUG
+endif
 zfs_include = $(srctree)/include/zfs
 icp_include = $(src)/icp/include
 zstd_include = $(src)/zstd/include
@@ -28,7 +36,6 @@ ZFS_MODULE_CFLAGS += -I$(zfs_include)/os/linux/spl
 ZFS_MODULE_CFLAGS += -I$(zfs_include)/os/linux/zfs
 ZFS_MODULE_CFLAGS += -I$(zfs_include)
 ZFS_MODULE_CPPFLAGS += -D_KERNEL
-ZFS_MODULE_CPPFLAGS += @KERNEL_DEBUG_CPPFLAGS@
 
 # KASAN enables -Werror=frame-larger-than=1024, which
 # breaks oh so many parts of our build.