crash test failing on non-tmpfs

[ajkr]

When run on non-tmpfs, python tools/db_crashtest.py blackbox --simple regularly fails with a MultiGet() error looking like this:

MultiGet error: IO error: Req failed: /tmp/rocksdb_crashtest_blackboxEJqTfu/009243.sst: Unknown error -22
MultiGet error: IO error: Req failed: /tmp/rocksdb_crashtest_blackboxEJqTfu/009255.sst: Unknown error -22
MultiGet error: IO error: Req failed: /tmp/rocksdb_crashtest_blackboxEJqTfu/009255.sst: Unknown error -22
MultiGet error: IO error: Req failed: /tmp/rocksdb_crashtest_blackboxEJqTfu/009255.sst: Unknown error -22
MultiGet error: IO error: Req failed: /tmp/rocksdb_crashtest_blackboxEJqTfu/009255.sst: Unknown error -22
MultiGet error: IO error: Req failed: /tmp/rocksdb_crashtest_blackboxEJqTfu/009243.sst: Unknown error -22

It's possible our CI always uses tmpfs which might have led us to miss this. cc @anand1976

[mrambacher]

Looking at this a little further, can someone explain to me what TEST_TMPDIR is supposed to mean? On Linux, it IS the test directory to run under. If it it set, the TestDirectory will exactly that value.
const char* env = getenv("TEST_TMPDIR");
if (env && env[0] != '\0') {
*result = env;
} else {
char buf[100];
snprintf(buf, sizeof(buf), "/tmp/rocksdbtest-%d", int(geteuid()));
*result = buf;
}

On Windows, it is a prefix:

const char* env = getenv("TEST_TMPDIR");
if (env && env[0] != '\0') {
output = env;
} else {
env = getenv("TMP");

if (env && env[0] != '\0') {
  output = env;
} else {
  output = "c:\\tmp";
}

}
CreateDir(output, opts, dbg);

output.append("\testrocksdb-");
output.append(std::to_string(GetCurrentProcessId()));

CreateDir(output, opts, dbg);

To me, it seems like they are both potentially wrong. If TEST_TMPDIR is meant to be a full-path, then Windows is wrong. If it is not meant to be a full path, then I think the Posix version should check the value of TMPDIR and not just assume /tmp.