Support C++ fstreams

[rgmiller]

System information

Type	Version/Name
Operating System	Linux
OS Version	Ubuntu 20.04 LTS
Architecture	x86_64
UnifyFS Version	current git HEAD

Describe the problem you're observing

It appears C++ fstreams are not handled properly by UnifyFS.

Describe how to reproduce the problem

It looks like pretty much any use of std::ifstream or std::ofstream will fail. I'll post some sample code below.

Include any warning or errors or releveant debugging data

For both std::ofstream and std::ifstream, opening the stream fails. For output streams, the file should have been created automatically, but it isn't. And for input streams, attempting to open a file that is known to exist still fails. The message from strerror(errno) in both cases is "No such file or directory".

[rgmiller]

GitHub won't let me attach a .cpp file, so I'm posting a simple bit of test code in this comment. Note that since the streams fail to open, this code never even gets to try reading or writing.

// Test UnifyFS using C++ fstreams

#include <unifyfs.h>
#include <unifyfs_rc.h>

#include <errno.h>
#include <string.h>

#include <iostream>
#include <fstream>
#include <string>

// The file we're going to read/write
//#define FNAME "/tmp/simple_test.txt"
#define FNAME "/unifyfs/simple_test.txt"

using namespace std;


int main( int argc, char **argv)
{
    
    int rc = unifyfs_mount("/unifyfs", 0, 1, 0);
    if (rc != UNIFYFS_SUCCESS) {
        cerr << "unifyfs_mount() failed.  Error code: " << rc << " - " << unifyfs_rc_enum_str((unifyfs_rc)rc) << endl;
        cerr << "Aborting." << endl;
        exit(-1);
    }

   
    // Try writing with C++ fstreams
    cout << "------- Writing using ofstream ------" << endl;
    ofstream outfile(FNAME);
    if (!outfile.good()) {
        string err(strerror(errno));
        cerr << "Failed to open ofstream.  Err msg: " << err << endl;
    } else {
        outfile << "This is a little bit of data written using std::ofstream." << endl;
        outfile.close();
    }
    cout << "-------------------------------------" << endl;

    
    // Try reading with C++ fstreams
    cout << "------- Reading using ifstream ------" << endl;
    ifstream infile(FNAME);
    if (! infile.good()) {
        string err(strerror(errno));
        cerr << "Failed to open ifstream.  Err msg: " << err << endl;
    } else {
        cout << "Contents of " << FNAME << ":" << endl;
        while (! infile.eof()) {
            string s;
            getline(infile, s);
            
            cout << s << endl;
        }
    }
    infile.close();
    cout << "-------------------------------------" << endl;
    
    
    rc = unifyfs_unmount();
    if (rc != UNIFYFS_SUCCESS) {
        cerr << "unifyfs_unmount() failed.  Error code: " << rc << endl;
    }
    
    return 0;
}