From 1c174e84c4e8d6a1a9b851b2132e07e5590fefb9 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, 5 Mar 2024 01:56:04 +0300
Subject: [PATCH] =?UTF-8?q?mdbx:=20=D0=B4=D0=BE=D0=B1=D0=B0=D0=B2=D0=BB?=
 =?UTF-8?q?=D0=B5=D0=BD=D0=B8=D0=B5=20`mdbx=5Fpreopen=5Fsnapinfo()`=20?=
 =?UTF-8?q?=D0=B2=20API.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

https://gitflic.ru/project/erthink/libmdbx/issue/15
---
 mdbx.h        | 12 ++++++++
 src/core.c    | 83 +++++++++++++++++++++++++++++++++++++++++++++++++++
 test/main.c++ |  8 +++++
 3 files changed, 103 insertions(+)

diff --git a/mdbx.h b/mdbx.h
index 1fda47e2..080b2509 100644
--- a/mdbx.h
+++ b/mdbx.h
@@ -5714,6 +5714,18 @@ LIBMDBX_API int mdbx_env_open_for_recoveryW(MDBX_env *env,
  * leg(s). */
 LIBMDBX_API int mdbx_env_turn_for_recovery(MDBX_env *env, unsigned target_meta);
 
+/** \brief FIXME
+ */
+LIBMDBX_API int mdbx_preopen_snapinfo(const char *pathname, MDBX_envinfo *arg,
+                                      size_t bytes);
+#if defined(_WIN32) || defined(_WIN64) || defined(DOXYGEN)
+/** \copydoc mdbx_preopen_snapinfo()
+ * \note Available only on Windows.
+ * \see mdbx_preopen_snapinfo() */
+LIBMDBX_API int mdbx_preopen_snapinfoW(const wchar_t *pathname,
+                                       MDBX_envinfo *arg, size_t bytes);
+#endif /* Windows */
+
 /** \brief Флаги/опции для проверки целостности БД.
  * \see mdbx_env_chk() */
 enum MDBX_chk_flags_t {
diff --git a/src/core.c b/src/core.c
index 666998b4..eb217b0a 100644
--- a/src/core.c
+++ b/src/core.c
@@ -23396,6 +23396,89 @@ __cold int env_info(const MDBX_env *env, const MDBX_txn *txn, MDBX_envinfo *out,
   }
 }
 
+__cold int mdbx_preopen_snapinfo(const char *pathname, MDBX_envinfo *out,
+                                 size_t bytes) {
+#if defined(_WIN32) || defined(_WIN64)
+  wchar_t *pathnameW = nullptr;
+  int rc = osal_mb2w(pathname, &pathnameW);
+  if (likely(rc == MDBX_SUCCESS)) {
+    rc = mdbx_preopen_snapinfoW(pathnameW, out, bytes);
+    osal_free(pathnameW);
+  }
+  return rc;
+}
+
+__cold int mdbx_preopen_snapinfoW(const wchar_t *pathname, MDBX_envinfo *out,
+                                  size_t bytes) {
+#endif /* Windows */
+  if (unlikely(!out))
+    return MDBX_EINVAL;
+
+  const size_t size_before_bootid = offsetof(MDBX_envinfo, mi_bootid);
+  const size_t size_before_pgop_stat = offsetof(MDBX_envinfo, mi_pgop_stat);
+  if (unlikely(bytes != sizeof(MDBX_envinfo)) && bytes != size_before_bootid &&
+      bytes != size_before_pgop_stat)
+    return MDBX_EINVAL;
+
+  memset(out, 0, bytes);
+  if (likely(bytes > size_before_bootid)) {
+    out->mi_bootid.current.x = bootid.x;
+    out->mi_bootid.current.y = bootid.y;
+  }
+
+  MDBX_env env;
+  memset(&env, 0, sizeof(env));
+  env.me_pid = osal_getpid();
+  const size_t os_psize = osal_syspagesize();
+  if (unlikely(!is_powerof2(os_psize) || os_psize < MIN_PAGESIZE)) {
+    ERROR("unsuitable system pagesize %" PRIuPTR, os_psize);
+    return MDBX_INCOMPATIBLE;
+  }
+  out->mi_sys_pagesize = env.me_os_psize = (unsigned)os_psize;
+  env.me_flags = MDBX_RDONLY | MDBX_NORDAHEAD | MDBX_ACCEDE | MDBX_VALIDATION;
+  env.me_stuck_meta = -1;
+  env.me_lfd = INVALID_HANDLE_VALUE;
+  env.me_lazy_fd = INVALID_HANDLE_VALUE;
+  env.me_dsync_fd = INVALID_HANDLE_VALUE;
+  env.me_fd4meta = INVALID_HANDLE_VALUE;
+#if defined(_WIN32) || defined(_WIN64)
+  env.me_data_lock_event = INVALID_HANDLE_VALUE;
+  env.me_overlapped_fd = INVALID_HANDLE_VALUE;
+#endif /* Windows */
+
+  int rc = env_handle_pathname(&env, pathname, 0);
+  if (unlikely(rc != MDBX_SUCCESS))
+    goto bailout;
+  rc = osal_openfile(MDBX_OPEN_DXB_READ, &env, env.me_pathname.dxb,
+                     &env.me_lazy_fd, 0);
+  if (unlikely(rc != MDBX_SUCCESS))
+    goto bailout;
+
+  MDBX_meta header;
+  rc = read_header(&env, &header, 0, 0);
+  if (unlikely(rc != MDBX_SUCCESS))
+    goto bailout;
+
+  setup_pagesize(&env, header.mm_psize);
+  out->mi_dxb_pagesize = env.me_psize;
+  out->mi_geo.lower = pgno2bytes(&env, header.mm_geo.lower);
+  out->mi_geo.upper = pgno2bytes(&env, header.mm_geo.upper);
+  out->mi_geo.shrink = pgno2bytes(&env, pv2pages(header.mm_geo.shrink_pv));
+  out->mi_geo.grow = pgno2bytes(&env, pv2pages(header.mm_geo.grow_pv));
+  out->mi_geo.current = pgno2bytes(&env, header.mm_geo.now);
+  out->mi_last_pgno = header.mm_geo.next - 1;
+
+  const unsigned n = 0;
+  out->mi_recent_txnid = constmeta_txnid(&header);
+  out->mi_meta_sign[n] = unaligned_peek_u64(4, &header.mm_sign);
+  if (likely(bytes > size_before_bootid))
+    memcpy(&out->mi_bootid.meta[n], &header.mm_bootid, 16);
+
+bailout:
+  env_close(&env, false);
+  return rc;
+}
+
 __cold int mdbx_env_info_ex(const MDBX_env *env, const MDBX_txn *txn,
                             MDBX_envinfo *arg, size_t bytes) {
   if (unlikely((env == NULL && txn == NULL) || arg == NULL))
diff --git a/test/main.c++ b/test/main.c++
index 84ab801c..8732f5f7 100644
--- a/test/main.c++
+++ b/test/main.c++
@@ -743,6 +743,14 @@ int main(int argc, char *const argv[]) {
     log_trace("=== done...");
   }
 
+  if (!failed) {
+    MDBX_envinfo info;
+    int err =
+        mdbx_preopen_snapinfo(params.pathname_db.c_str(), &info, sizeof(info));
+    if (err != MDBX_SUCCESS)
+      failure_perror("mdbx_preopen_snapinfo()", err);
+  }
+
   log_notice("RESULT: %s\n", failed ? "Failed" : "Successful");
   if (global::config::cleanup_after) {
     if (failed)