[PATCH v5][makedumpfile 7/9] Add sample extension as an example reference

[Tao Liu <ltao@redhat.com>]

This patch will add a sample.c as an example extension for code
reference. The extension will do nothing related to page filtering,
but print a few kernel symbol/type information.

Suggested-by: Kazuhito Hagio <k-hagio-ab@nec.com>
Signed-off-by: Tao Liu <ltao@redhat.com>
---
 extensions/Makefile |  2 +-
 extensions/sample.c | 69 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 70 insertions(+), 1 deletion(-)
 create mode 100644 extensions/sample.c

diff --git a/extensions/Makefile b/extensions/Makefile
index b23f346..dbaec4e 100644
--- a/extensions/Makefile
+++ b/extensions/Makefile
@@ -1,5 +1,5 @@
 CC ?= gcc
-CONTRIB_SO :=
+CONTRIB_SO := sample.so
 
 all: $(CONTRIB_SO)
 
diff --git a/extensions/sample.c b/extensions/sample.c
new file mode 100644
index 0000000..e4938d1
--- /dev/null
+++ b/extensions/sample.c
@@ -0,0 +1,69 @@
+#include "../makedumpfile.h"
+#include "../btf_info.h"
+#include "../kallsyms.h"
+#include "../extension.h"
+
+/* 
+ * Declare the kernel symbols/types that will be used by the extension later.
+ * The btf/kallsyms component of makedumpfile will resolve these requested
+ * info automatically during extension loading.
+ * 
+ * The symbol/types declared by non-OPT macros as INIT_MOD_XX are must-have for
+ * the extension, any missing of these will lead to load-fail of the extension.
+ * This is useful to skip one extension as early. E.g. exit the amdgpu mm filtering
+ * extension when filtering against a vmcore dumpped by a machine which have
+ * no amdgpu hardware.
+ * 
+ * The symbol/types declared by OPT macros as INIT_OPT_MOD_XX are optional,
+ * meaning the existence of these are checked during extension runtime. This
+ * is useful to cover different kernel versions where some of the data structure
+ * are slightly different.
+ */
+/* All kernel will have init_task and task_struct.mm */
+INIT_MOD_SYM(vmlinux, init_task);
+INIT_MOD_STRUCT_MEMBER(vmlinux, task_struct, mm);
+/* 
+ * Older kernels use mm_struct.mm_rb,
+ * later ones use mm_struct.mm_mt
+ */
+INIT_OPT_MOD_STRUCT_MEMBER(vmlinux, mm_struct, mm_mt);
+INIT_OPT_MOD_STRUCT_MEMBER(vmlinux, mm_struct, mm_rb);
+
+/*
+ * Extension callback when makedumpfile is doing page filtering,
+ * extension should decide whether the given page should be kept(PG_INCLUDE),
+ * discarded(PG_EXCLUDE) or undecided(PG_UNDECID). Here we simply return
+ * PG_UNDECID to let every page fallbacks to traditinal page-flags
+ * check routine or let other extensions make the decision.
+ */
+int extension_callback(unsigned long pfn, const void *pcache)
+{
+	return PG_UNDECID;
+}
+
+/* Entry of extension */
+void extension_init(void)
+{
+	MSG("sample.so: The address of init_task is: %lx\n",
+		GET_MOD_SYM(vmlinux, init_task));
+	MSG("sample.so: The size of task_struct is: %d bytes\n",
+		GET_MOD_STRUCT_MEMBER_SSIZE(vmlinux, task_struct, mm));
+	MSG("sample.so: The offset of member mm within task_struct is: %d bytes\n",
+		GET_MOD_STRUCT_MEMBER_MOFF(vmlinux, task_struct, mm) / 8 );
+	MSG("sample.so: The size of member mm within task_struct is: %d bytes\n",
+		GET_MOD_STRUCT_MEMBER_MSIZE(vmlinux, task_struct, mm));
+	if (MOD_STRUCT_MEMBER_EXIST(vmlinux, mm_struct, mm_mt)) {
+		MSG("sample.so: Your kernel is using maple tree in mm_struct\n");
+	}
+	if (MOD_STRUCT_MEMBER_EXIST(vmlinux, mm_struct, mm_rb)) {
+		MSG("sample.so: Your kernel is using rb tree in mm_struct\n");
+	}
+}
+
+/* 
+ * This function is called when the extension is unloaded. 
+ * If desired, perform any cleanups here. 
+ */
+__attribute__((destructor))
+void extension_cleanup(void) { }
+
-- 
2.47.0