Merge bitcoin#15650: Handle the result of posix_fallocate system call

5d35ae3 Handle the result of posix_fallocate system call (Luca Venturini)

Pull request description:

  The system call `posix_fallocate` is not supported on some filesystems.

  - catches the result of posix_allocate and fall back to the default behaviour if the return value is different from 0 (success)

  Fixes bitcoin#15624

ACKs for commit 5d35ae:
  MarcoFalke:
    utACK 5d35ae3
  sipa:
    utACK 5d35ae3, though the Yoda condition is an uncommon style in this project.
  hebasto:
    utACK 5d35ae3
  practicalswift:
    utACK 5d35ae3

Tree-SHA512: 7ab3b35fb633926f28a58b2b07ffde8e31bb997c80a716b1b45ee716fe9ff4ddcef0a05810bd4423530e220cfc62f8925517d27a8b92b05a524272063e43f746

src/util.cpp

@@ -1015,11 +1015,12 @@ void AllocateFileRange(FILE *file, unsigned int offset, unsigned int length) {
         fcntl(fileno(file), F_PREALLOCATE, &fst);
     }
     ftruncate(fileno(file), fst.fst_length);
-#elif defined(__linux__)
+#else
+    #if defined(__linux__)
     // Version using posix_fallocate
     off_t nEndPos = (off_t)offset + length;
-    posix_fallocate(fileno(file), 0, nEndPos);
-#else
+    if (0 == posix_fallocate(fileno(file), 0, nEndPos)) return;
+    #endif
     // Fallback version
     // TODO: just write one byte per block
     static const char buf[65536] = {};