mdbx: crutch for WSL.

Fixes https://github.com/erthink/libmdbx/issues/97

Change-Id: Ia863ffc8cd939b1af65f21ab0c5c8197abf4e793

README.md

@@ -421,6 +421,12 @@ To build _libmdbx_ for iOS, we recommend using CMake using the
 "[toolchain file](https://cmake.org/cmake/help/latest/variable/CMAKE_TOOLCHAIN_FILE.html)"
 from the [ios-cmake](https://github.com/leetal/ios-cmake) project.
 
+### Windows Subsystem for Linux
+_libmdbx_ could be using in [WSL2](https://en.wikipedia.org/wiki/Windows_Subsystem_for_Linux#WSL_2)
+but NOT in [WSL1](https://en.wikipedia.org/wiki/Windows_Subsystem_for_Linux#WSL_1) environment.
+This is a consequence of the fundamental shortcomings of _WSL1_ and cannot be fixed.
+To avoid data loss, _libmdbx_ returns the `ENOLCK` (37, "No record locks available")
+error when opening the database in a _WSL1_ environment.
 
 ## API description
 For more information and API description see the [mdbx.h](mdbx.h) header.

src/elements/lck-posix.c

@@ -24,15 +24,25 @@
 #include <sys/utsname.h>
 #ifndef MDBX_ALLOY
 uint32_t mdbx_linux_kernel_version;
+bool mdbx_RunningOnWSL;
 #endif /* MDBX_ALLOY */
 #endif /* Linux */
 
+static __cold unsigned probe_for_WSL(const char *tag) {
+  /* "Official" way of detecting WSL but not WSL2
+   * https://github.com/Microsoft/WSL/issues/423#issuecomment-221627364 */
+  return strstr(tag, "Microsoft") || strstr(tag, "WSL");
+}
+
 static __cold __attribute__((__constructor__)) void
 mdbx_global_constructor(void) {
 #if defined(__linux__) || defined(__gnu_linux__)
   struct utsname buffer;
   if (uname(&buffer) == 0) {
     int i = 0;
+    mdbx_RunningOnWSL = probe_for_WSL(buffer.version) ||
+                        probe_for_WSL(buffer.sysname) ||
+                        probe_for_WSL(buffer.release);
     char *p = buffer.release;
     while (*p && i < 4) {
       if (*p >= '0' && *p <= '9') {
@@ -292,6 +302,17 @@ MDBX_INTERNAL_FUNC int __cold mdbx_lck_seize(MDBX_env *env) {
 #endif /* MDBX_USE_OFDLOCKS */
 
   int rc = MDBX_SUCCESS;
+#if defined(__linux__) || defined(__gnu_linux__)
+  if (unlikely(mdbx_RunningOnWSL)) {
+    rc = ENOLCK;
+    mdbx_error("%s, err %u",
+               "WSL (Windows Subsystem for Linux) is mad and trouble-full, "
+               "injecting failure to avoid data loss",
+               rc);
+    return rc /* No record locks available */;
+  }
+#endif /* Linux */
+
   if (env->me_lfd == INVALID_HANDLE_VALUE) {
     /* LY: without-lck mode (e.g. exclusive or on read-only filesystem) */
     rc =

src/elements/osal.h

@@ -497,6 +497,8 @@ MDBX_INTERNAL_FUNC int mdbx_vasprintf(char **strp, const char *fmt, va_list ap);
 
 #if defined(__linux__) || defined(__gnu_linux__)
 MDBX_INTERNAL_VAR uint32_t mdbx_linux_kernel_version;
+MDBX_INTERNAL_VAR bool
+    mdbx_RunningOnWSL /* Windows Subsystem for Linux is mad and trouble-full */;
 #endif /* Linux */
 
 /* Get the size of a memory page for the system.