From de63041b7d4a165fb82a9261aec9331393164e56 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=9B=D0=B5=D0=BE=D0=BD=D0=B8=D0=B4=20=D0=AE=D1=80=D1=8C?=
 =?UTF-8?q?=D0=B5=D0=B2=20=28Leonid=20Yuriev=29?= <leo@yuriev.ru>
Date: Tue, 22 Mar 2022 20:40:30 +0300
Subject: [PATCH] mdbx: add `MDBX_DBG_DONT_UPGRADE` flag.

---
 mdbx.h         | 11 ++++++++---
 src/core.c     |  9 ++++++---
 src/mdbx_chk.c |  2 +-
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/mdbx.h b/mdbx.h
index 3844afc5..1e71f1ad 100644
--- a/mdbx.h
+++ b/mdbx.h
@@ -864,18 +864,23 @@ enum MDBX_debug_flags_t {
   MDBX_DBG_JITTER = 4,
 
   /** Include or not meta-pages in coredump files.
-   * May affect performance in \ref MDBX_WRITEMAP mode */
+   * \note May affect performance in \ref MDBX_WRITEMAP mode */
   MDBX_DBG_DUMP = 8,
 
   /** Allow multi-opening environment(s) */
   MDBX_DBG_LEGACY_MULTIOPEN = 16,
 
-  /** Allow read and write transactions overlapping for the same thread */
+  /** Allow read and write transactions overlapping for the same thread. */
   MDBX_DBG_LEGACY_OVERLAP = 32,
 
+  /** Don't auto-upgrade format signature.
+   * \note However a new write transactions will use and store
+   * the last signature regardless this flag */
+  MDBX_DBG_DONT_UPGRADE = 64,
+
 #ifdef ENABLE_UBSAN
   MDBX_DBG_MAX = ((unsigned)MDBX_LOG_MAX) << 16 |
-                 63 /* avoid UBSAN false-positive trap by a tests */,
+                 127 /* avoid UBSAN false-positive trap by a tests */,
 #endif /* ENABLE_UBSAN */
 
   /** for mdbx_setup_debug() only: Don't change current settings */
diff --git a/src/core.c b/src/core.c
index 3fb5d0fb..8a6866fb 100644
--- a/src/core.c
+++ b/src/core.c
@@ -12278,7 +12278,8 @@ __cold static int mdbx_setup_dxb(MDBX_env *env, const int lck_rc,
     atomic_store32(&env->me_lck->mti_discarded_tail,
                    bytes2pgno(env, used_aligned2os_bytes), mo_Relaxed);
 
-    if ((env->me_flags & MDBX_RDONLY) == 0 && env->me_stuck_meta < 0) {
+    if ((env->me_flags & MDBX_RDONLY) == 0 && env->me_stuck_meta < 0 &&
+        (mdbx_runtime_flags & MDBX_DBG_DONT_UPGRADE) == 0) {
       for (int n = 0; n < NUM_METAS; ++n) {
         MDBX_meta *const pmeta = METAPAGE(env, n);
         if (unlikely(unaligned_peek_u64(4, &pmeta->mm_magic_and_version) !=
@@ -12618,7 +12619,8 @@ __cold static int __must_check_result mdbx_override_meta(
   mdbx_assert(env, meta_checktxnid(env, model, true));
   if (shape) {
     mdbx_assert(env, meta_checktxnid(env, shape, true));
-    if (env->me_stuck_meta >= 0)
+    if (env->me_stuck_meta >= 0 ||
+        (mdbx_runtime_flags & MDBX_DBG_DONT_UPGRADE) != 0)
       memcpy(&model->mm_magic_and_version, &shape->mm_magic_and_version,
              sizeof(model->mm_magic_and_version));
     model->mm_extra_flags = shape->mm_extra_flags;
@@ -20877,7 +20879,8 @@ __cold int mdbx_setup_debug(int loglevel, int flags, MDBX_debug_func *logger) {
 #if MDBX_DEBUG
         MDBX_DBG_ASSERT | MDBX_DBG_AUDIT | MDBX_DBG_JITTER |
 #endif
-        MDBX_DBG_DUMP | MDBX_DBG_LEGACY_MULTIOPEN | MDBX_DBG_LEGACY_OVERLAP;
+        MDBX_DBG_DUMP | MDBX_DBG_LEGACY_MULTIOPEN | MDBX_DBG_LEGACY_OVERLAP |
+        MDBX_DBG_DONT_UPGRADE;
     mdbx_runtime_flags = (uint8_t)flags;
   }
 
diff --git a/src/mdbx_chk.c b/src/mdbx_chk.c
index 455acb8c..62dfcd24 100644
--- a/src/mdbx_chk.c
+++ b/src/mdbx_chk.c
@@ -1226,7 +1226,7 @@ int main(int argc, char *argv[]) {
   mdbx_setup_debug((verbose < MDBX_LOG_TRACE - 1)
                        ? (MDBX_log_level_t)(verbose + 1)
                        : MDBX_LOG_TRACE,
-                   MDBX_DBG_LEGACY_OVERLAP, logger);
+                   MDBX_DBG_LEGACY_OVERLAP | MDBX_DBG_DONT_UPGRADE, logger);
 
   rc = mdbx_env_create(&env);
   if (rc) {