From fe20de136c22ed3bc4c6d3f673e79c106e824f60 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: Sun, 18 Sep 2022 13:21:38 +0300
Subject: [PATCH] mdbx: require linux >= 4.0

---
 src/core.c | 11 +++++++++++
 src/osal.c | 13 ++++++-------
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/src/core.c b/src/core.c
index 4352545e..a1f635d0 100644
--- a/src/core.c
+++ b/src/core.c
@@ -11499,6 +11499,17 @@ __cold int mdbx_env_create(MDBX_env **penv) {
     return MDBX_INCOMPATIBLE;
   }
 
+#if defined(__linux__) || defined(__gnu_linux__)
+  if (unlikely(linux_kernel_version < 0x04000000)) {
+    /* 2022-09-01: Прошло уже больше двух после окончания какой-либо поддержки
+     * самого "долгоиграющего" ядра 3.16.85 ветки 3.x */
+    ERROR("too old linux kernel %u.%u.%u.%u, the >= 4.0.0 is required",
+          linux_kernel_version >> 24, (linux_kernel_version >> 16) & 255,
+          (linux_kernel_version >> 8) & 255, linux_kernel_version & 255);
+    return MDBX_INCOMPATIBLE;
+  }
+#endif /* Linux */
+
   MDBX_env *env = osal_calloc(1, sizeof(MDBX_env));
   if (unlikely(!env))
     return MDBX_ENOMEM;
diff --git a/src/osal.c b/src/osal.c
index a3e23eee..ec26357c 100644
--- a/src/osal.c
+++ b/src/osal.c
@@ -937,9 +937,8 @@ MDBX_INTERNAL_FUNC int osal_fsync(mdbx_filehandle_t fd,
       break /* error */;
 #if defined(__linux__) || defined(__gnu_linux__)
     case MDBX_SYNC_SIZE:
-      if (linux_kernel_version >= 0x03060000)
-        return MDBX_SUCCESS;
-      __fallthrough /* fall through */;
+      assert(linux_kernel_version >= 0x03060000);
+      return MDBX_SUCCESS;
 #endif /* Linux */
 #endif /* _POSIX_SYNCHRONIZED_IO > 0 */
     default:
@@ -1076,10 +1075,10 @@ MDBX_INTERNAL_FUNC int osal_msync(osal_mmap_t *map, size_t offset,
     return (int)GetLastError();
 #else
 #if defined(__linux__) || defined(__gnu_linux__)
-  if (mode_bits == MDBX_SYNC_NONE && linux_kernel_version > 0x02061300)
-    /* Since Linux 2.6.19, MS_ASYNC is in fact a no-op. The kernel properly
-     * tracks dirty pages and flushes them to storage as necessary. */
-    return MDBX_SUCCESS;
+  assert(linux_kernel_version > 0x02061300);
+  /* Since Linux 2.6.19, MS_ASYNC is in fact a no-op. The kernel properly
+   * tracks dirty pages and flushes them to storage as necessary. */
+  return MDBX_SUCCESS;
 #endif /* Linux */
   if (msync(ptr, length, (mode_bits & MDBX_SYNC_DATA) ? MS_SYNC : MS_ASYNC))
     return errno;