mdbx: conditionally use cacheflush() for linux < 2.6.11

Change-Id: Id34c67797e14f709f767bf1b687319cd2dfef874

src/lck-linux.c

@@ -19,6 +19,7 @@
 #endif
 
 #include "./bits.h"
+#include <sys/utsname.h>
 
 /* Some platforms define the EOWNERDEAD error code
  * even though they don't support Robust Mutexes.
@@ -36,10 +37,31 @@
 #endif
 #endif /* MDBX_USE_ROBUST */
 
+uint32_t linux_kernel_version;
+
 /*----------------------------------------------------------------------------*/
 /* rthc */
 
 static __cold __attribute__((constructor)) void mdbx_global_constructor(void) {
+  struct utsname buffer;
+  if (uname(&buffer) == 0) {
+    int i = 0;
+    char *p = buffer.release;
+    while (*p && i < 4) {
+      if (*p >= '0' && *p <= '9') {
+        long number = strtol(p, &p, 10);
+        if (number > 0) {
+          if (number > 255)
+            number = 255;
+          linux_kernel_version += number << (24 - i * 8);
+        }
+        ++i;
+      } else {
+        ++p;
+      }
+    }
+  }
+
   mdbx_rthc_global_init();
 }
 

src/mdbx.c

@@ -4639,9 +4639,17 @@ static int mdbx_page_flush(MDBX_txn *txn, pgno_t keep) {
           mdbx_debug("Write error: %s", mdbx_strerror(rc));
           return rc;
         }
-#if MDBX_CPU_CACHE_MMAP_NONCOHERENT == 1
+
+#if MDBX_CPU_CACHE_MMAP_NONCOHERENT
+#if defined(__linux__) || defined(__gnu_linux__)
+        if (linux_kernel_version >= 0x02060b00)
+        /* Linux kernels older than version 2.6.11 ignore the addr and nbytes
+         * arguments, making this function fairly expensive. Therefore, the
+         * whole cache is always flushed. */
+#endif /* Linux */
           mdbx_invalidate_mmap_noncoherent_cache(env->me_map + wpos, wsize);
-#endif
+#endif /* MDBX_CPU_CACHE_MMAP_NONCOHERENT */
+
         n = 0;
       }
       if (i > pagecount)
@@ -4657,13 +4665,16 @@ static int mdbx_page_flush(MDBX_txn *txn, pgno_t keep) {
     n++;
   }
 
-#if MDBX_CPU_CACHE_MMAP_NONCOHERENT > 1
+#if MDBX_CPU_CACHE_MMAP_NONCOHERENT &&                                         \
+    (defined(__linux__) || defined(__gnu_linux__))
+  if (linux_kernel_version < 0x02060b00) {
     /* Linux kernels older than version 2.6.11 ignore the addr and nbytes
      * arguments, making this function fairly expensive. Therefore, the whole
      * cache is always flushed. */
     mdbx_invalidate_mmap_noncoherent_cache(env->me_map,
                                            pgno2bytes(env, txn->mt_next_pgno));
-#endif
+  }
+#endif /* MDBX_CPU_CACHE_MMAP_NONCOHERENT && Linux */
 
   for (i = keep; ++i <= pagecount;) {
     dp = dl[i].ptr;

src/osal.h

@@ -462,6 +462,10 @@ int mdbx_vasprintf(char **strp, const char *fmt, va_list ap);
 /* max bytes to write in one call */
 #define MAX_WRITE UINT32_C(0x3fff0000)
 
+#if defined(__linux__) || defined(__gnu_linux__)
+extern uint32_t linux_kernel_version;
+#endif /* Linux */
+
 /* Get the size of a memory page for the system.
  * This is the basic size that the platform's memory manager uses, and is
  * fundamental to the use of memory-mapped files. */