mdbx: add MDBX_DBG_DUMP for mdbx_setup_debug().

So, meta-pages and lck-section now will be included into a coredump.

mdbx.h

@@ -1567,6 +1567,7 @@ LIBMDBX_API MDBX_oom_func *mdbx_env_get_oomfunc(MDBX_env *env);
 #define MDBX_DBG_EXTRA 8
 #define MDBX_DBG_AUDIT 16
 #define MDBX_DBG_JITTER 32
+#define MDBX_DBG_DUMP 64
 
 typedef void MDBX_debug_func(int type, const char *function, int line,
                              const char *msg, va_list args);

src/mdbx.c

@@ -9859,6 +9859,32 @@ int __cold mdbx_reader_check0(MDBX_env *env, int rdt_locked, int *dead) {
 int __cold mdbx_setup_debug(int flags, MDBX_debug_func *logger) {
   unsigned ret = mdbx_runtime_flags;
   mdbx_runtime_flags = flags;
+
+#ifdef __linux__
+  if (flags & MDBX_DBG_DUMP) {
+    int core_filter_fd = open("/proc/self/coredump_filter", O_TRUNC | O_RDWR);
+    if (core_filter_fd >= 0) {
+      char buf[32];
+      const unsigned r = pread(core_filter_fd, buf, sizeof(buf), 0);
+      if (r > 0 && r < sizeof(buf)) {
+        buf[r] = 0;
+        unsigned long mask = strtoul(buf, NULL, 16);
+        if (mask != ULONG_MAX) {
+          mask |= 1 << 3 /* Dump file-backed shared mappings */;
+          mask |= 1 << 6 /* Dump shared huge pages */;
+          mask |= 1 << 8 /* Dump shared DAX pages */;
+          unsigned w = snprintf(buf, sizeof(buf), "0x%lx\n", mask);
+          if (w > 0 && w < sizeof(buf)) {
+            w = pwrite(core_filter_fd, buf, w, 0);
+            (void)w;
+          }
+        }
+      }
+      close(core_filter_fd);
+    }
+  }
+#endif /* __linux__ */
+
   mdbx_debug_logger = logger;
   return ret;
 }

test/base.h

@@ -37,8 +37,11 @@
 #if defined(_WIN32) || defined(_WIN64) || defined(_WINDOWS)
 #include <io.h>
 #else
+#include <fcntl.h>
 #include <sys/param.h>
+#include <sys/stat.h>
 #include <sys/time.h>
+#include <sys/types.h>
 #include <unistd.h>
 #endif
 

test/test.cc

@@ -114,7 +114,7 @@ void testcase::db_prepare() {
   log_trace(">> db_prepare");
   assert(!db_guard);
 
-  int mdbx_dbg_opts = MDBX_DBG_ASSERT | MDBX_DBG_JITTER;
+  int mdbx_dbg_opts = MDBX_DBG_ASSERT | MDBX_DBG_JITTER | MDBX_DBG_DUMP;
   if (config.params.loglevel <= logging::trace)
     mdbx_dbg_opts |= MDBX_DBG_TRACE;
   if (config.params.loglevel <= logging::verbose)