lib/filesystem.js

// -------------------------------------------------
// ----------------- FILESYSTEM---------------------
// -------------------------------------------------
// Implementation of a unix filesystem in memory.

"use strict";

var S_IRWXUGO = 0x1FF;
var S_IFMT = 0xF000;
var S_IFSOCK = 0xC000;
var S_IFLNK = 0xA000;
var S_IFREG = 0x8000;
var S_IFBLK = 0x6000;
var S_IFDIR = 0x4000;
var S_IFCHR = 0x2000;

//var S_IFIFO  0010000
//var S_ISUID  0004000
//var S_ISGID  0002000
//var S_ISVTX  0001000

var O_RDONLY = 0x0000; // open for reading only 
var O_WRONLY = 0x0001; // open for writing only
var O_RDWR = 0x0002; // open for reading and writing
var O_ACCMODE = 0x0003; // mask for above modes

var STATUS_INVALID = -0x1;
var STATUS_OK = 0x0;
var STATUS_OPEN = 0x1;
var STATUS_ON_SERVER = 0x2;
var STATUS_LOADING = 0x3;
var STATUS_UNLINKED = 0x4;


/** @const */
var DEFAULT_MODE = 420; // 0o644, the most common one

/** @const */
var TYPE_DIR = 0;
/** @const */
var TYPE_FILE = 1;
/** @const */
var TYPE_LINK = 2;

/** @constructor */
function FS(baseurl) {
    this.inodes = [];
    this.events = [];

    this.baseurl = baseurl;

    this.qidnumber = 0x0;
    this.filesinloadingqueue = 0;
    this.OnLoaded = function() {};

    //this.tar = new TAR(this);
    this.userinfo = [];

    this.inodedata = {};
    

    //RegisterMessage("LoadFilesystem", this.LoadFilesystem.bind(this) );
    //RegisterMessage("MergeFile", this.MergeFile.bind(this) );
    //RegisterMessage("tar",
    //    function(data) {
    //        SendToMaster("tar", this.tar.Pack(data));
    //    }.bind(this)
    //);
    //RegisterMessage("sync",
    //    function(data) {
    //        SendToMaster("sync", this.tar.Pack(data));
    //    }.bind(this)
    //);

    // root entry
    this.CreateDirectory("", -1);

    this._state_skip = ["OnLoaded"];
}


// -----------------------------------------------------
FS.prototype.LoadFilesystem = function(userinfo)
{
    this.userinfo = userinfo;
    this.LoadFSXML(this.userinfo.basefsURL);
}


// -----------------------------------------------------

FS.prototype.AddEvent = function(id, OnEvent) {
    var inode = this.inodes[id];
    if (inode.status == STATUS_OK) {
        OnEvent();
        return;
    }
    this.events.push({id: id, OnEvent: OnEvent});    
}

FS.prototype.HandleEvent = function(id) {
    if (this.filesinloadingqueue == 0) {
        this.OnLoaded();
        this.OnLoaded = function() {};
    }
    //DebugMessage("number of events: " + this.events.length);
    for(var i = this.events.length - 1; i >= 0; i--) {
        if (this.events[i].id != id) continue;
        this.events[i].OnEvent();
        this.events.splice(i, 1);
    }
}


// -----------------------------------------------------
//FS.prototype.LoadImage = function(url)
//{
//    dbg_assert(false);
//    if (!url) return;
//    //DebugMessage("Load Image " + url);
///*
//    if (typeof Worker !== 'undefined') {
//        LoadBZIP2Resource(url, 
//            function(m){ for(var i=0; i<m.size; i++) this.tar.Unpack(m.data[i]); }.bind(this), 
//            function(e){DebugMessage("Error: Could not load " + url + ". Skipping.");});
//        return;
//    }
//*/
//    LoadBinaryResource(url,
//    function(buffer){
//        var buffer8 = new Uint8Array(buffer);
//        bzip2.simple(buffer8, this.tar.Unpack.bind(this.tar));
//    }.bind(this),
//    function(error){DebugMessage("Error: Could not load " + url + ". Skipping.");});
//}
// -----------------------------------------------------


function ReadVariable(buffer, offset) {
    var variable = [];
    variable.name = "";
    variable.value = "";

    // read blanks
    for(var i=offset; i<buffer.length; i++) {
        if (buffer[i] == '>') return variable;
        if (buffer[i] == '/') return variable;
        if (buffer[i] != ' ') break;
    }
    offset = i;
    if (buffer[i] == '>') return variable;

    // read variable name
    for(var i=offset; i<buffer.length; i++) {
        if (buffer[i] == '>') break;
        if (buffer[i] == '=') break;
        variable.name = variable.name + buffer[i]; 
    }
    offset = i+1;
    if (variable.name.length == 0) return variable;
    // read variable value
    for(var i=offset+1; i<buffer.length; i++) {
        if (buffer[i] == '>') break;
        if (buffer[i] == '\'') break;
        variable.value = variable.value + buffer[i]; 
    }
    offset = i+1;
    variable.offset = offset;
    DebugMessage("read " + variable.name + "=" + variable.value);
    return variable;
}

function ReadTag(buffer, offset) {
    var tag = [];
    tag.type = "";
    tag.name = "";
    tag.mode = 0x0;
    tag.uid = 0x0;
    tag.gid = 0x0;
    tag.path = "";
    tag.src = "";
    tag.compressed = false;
    tag.load = false;

    if (buffer[offset] != '<') return tag;
    for(var i=offset+1; i<buffer.length; i++) {
        if (buffer[i] ==  ' ') break;
        if (buffer[i] == '\n') break;
        if (buffer[i] == '>') break;
        tag.type = tag.type + buffer[i]; 
    }
    offset = i;
    // read variables
    do {
        var variable = ReadVariable(buffer, offset);
        if (variable.name == "name") tag.name = variable.value;
        if (variable.name == "mode") tag.mode = parseInt(variable.value, 8);
        if (variable.name == "uid") tag.uid = parseInt(variable.value, 10);
        if (variable.name == "gid") tag.gid = parseInt(variable.value, 10);
        if (variable.name == "path") tag.path = variable.value;
        if (variable.name == "size") tag.size = parseInt(variable.value, 10);
        if (variable.name == "src") tag.src = variable.value;
        if (variable.name == "compressed") tag.compressed = true;
        if (variable.name == "load") tag.load = true;
        offset = variable.offset;
    } while(variable.name.length != 0);
    return tag;
};

FS.prototype.CheckEarlyload = function(path)
{
    for(var i=0; i<this.userinfo.earlyload.length; i++) {
        if (this.userinfo.earlyload[i] == path) {
            return true;
        }
    }
    return false;
}

FS.prototype.LoadFSXML = function(url)
{
    DebugMessage("Load filesystem information from " + url);

    LoadXMLResource(url, this.OnJSONLoaded.bind(this), function(error){throw error;});
}

FS.prototype.OnJSONLoaded = function(fs)
{
    //console.time("parse");
    var fsroot = JSON.parse(fs)["fsroot"];
    //console.timeEnd("parse");
    
    var me = this;

    setTimeout(function()
    {
        console.time("Load");
        //console.profile("Load");
        for(var i = 0; i < fsroot.length; i++) {
            me.LoadRecursive(fsroot[i], 0);
        }
        //console.profileEnd("Load");
        console.timeEnd("Load");
        
        if(DEBUG)
        {
            //console.time("Check");
            //me.Check();
            //console.timeEnd("Check");
        }

        me.OnLoaded();
        me.OnLoaded = function() {};
    }, 0);
};

FS.prototype.LoadRecursive = function(data, parentid)
{
    var inode = this.CreateInode();

    inode.name = data.name;
    inode.uid = data.uid || 0;
    inode.gid = data.gid || 0;
    inode.ctime = data.ctime || Math.floor(Date.now() / 1000);
    inode.mtime = data.mtime || inode.ctime;
    inode.atime = data.atime || inode.ctime;
    inode.parentid = parentid;
    inode.mode = data.mode === undefined ? DEFAULT_MODE : (data.mode & 511);
    inode.size = data.size || 0;

    //window.modes[inode.mode] = window.modes[inode.mode] + 1 | 0;

    if(data.type === TYPE_DIR)
    {
        this.LoadDir(inode, data.children);
    }
    else if(data.type === TYPE_FILE)
    {
        inode.mode |= S_IFREG;
        //var idx = this.inodes.length;
        inode.status = STATUS_ON_SERVER;
        this.PushInode(inode);
        //var url = this.baseurl + this.GetFullPath(idx);
        //inode.url = url;
    }
    else
    {
        dbg_assert(data.type === TYPE_LINK);
        inode.mode |= S_IFLNK;
        inode.symlink = data.target;
        this.PushInode(inode);
    }
}

FS.prototype.LoadDir = function(inode, children)
{
    inode.updatedir = true;
    inode.mode |= S_IFDIR;
    var p = this.inodes.length;
    this.PushInode(inode);
    for(var i = 0; i < children.length; i++) {
        this.LoadRecursive(children[i], p);
    }
}

// The filesystem is responsible to add the correct time. This is a hack
// Have to find a better solution.
FS.prototype.AppendDateHack = function(idx) {
    if (this.GetFullPath(idx) != "etc/init.d/rcS") return; 
    var inode = this.inodes[idx];
    var date = new Date();
    var datestring = 
        "\ndate -s \"" + 
        date.getFullYear() + 
        "-" + 
        (date.getMonth()+1) + 
        "-" + 
        date.getDate() + 
        " " + 
        date.getHours() +
        ":" + 
        date.getMinutes() +
        ":" + 
        date.getSeconds() +
        "\"\n";
    var size = inode.size;
    this.ChangeSize(idx, size+datestring.length);
    var data = this.inodedata[idx];
    for(var i=0; i<datestring.length; i++) {
        data[i+size] = datestring.charCodeAt(i); 
    }
}


// Loads the data from a url for a specific inode
FS.prototype.LoadFile = function(idx) {
    var inode = this.inodes[idx];
    if (inode.status != STATUS_ON_SERVER) {
        return;
    }
    inode.status = STATUS_LOADING;
    this.filesinloadingqueue++;

    //if (inode.compressed) {
    //    inode.data = new Uint8Array(inode.size);
    //    LoadBinaryResource(inode.url + ".bz2",
    //    function(buffer){
    //        var buffer8 = new Uint8Array(buffer);
    //        var ofs = 0;
    //        bzip2.simple(buffer8, function(x){inode.data[ofs++] = x;}.bind(this) );    
    //        inode.status = STATUS_OK;
    //        this.filesinloadingqueue--;
    //        this.HandleEvent(idx);            
    //    }.bind(this), 
    //    function(error){throw error;});
    //    return;
    //}

    LoadBinaryResource(this.baseurl + this.GetFullPath(inode.fid),  
        function(buffer){
            var data = this.inodedata[idx] = new Uint8Array(buffer);
            inode.size = data.length; // correct size if the previous was wrong. 
            inode.status = STATUS_OK;
            //if (inode.name == "rcS") {
            //    this.AppendDateHack(idx);
            //}
            this.filesinloadingqueue--;
            this.HandleEvent(idx);            
        }.bind(this), 
        function(error){throw error;});

}

// -----------------------------------------------------

FS.prototype.PushInode = function(inode) {
    if (inode.parentid != -1) {
        this.inodes.push(inode);
        inode.fid = this.inodes.length - 1;
        this.inodes[inode.parentid].updatedir = true;
        inode.nextid = this.inodes[inode.parentid].firstid;
        this.inodes[inode.parentid].firstid = this.inodes.length-1;
        return;
    } else {
        if (this.inodes.length == 0) { // if root directory
            this.inodes.push(inode);
            return;
        }
    }

    DebugMessage("Error in Filesystem: Pushed inode with name = "+ inode.name + " has no parent");
    abort();
}

/** @constructor */
function Inode(qidnumber)
{
    this.updatedir = false; // did the directory listing changed?
    this.parentid= -1;
    this.firstid = -1; // first file id in directory
    this.nextid = -1; // next id in directory
    this.status = 0;
    this.name = "";
    this.size = 0x0;
    this.uid = 0x0;
    this.gid = 0x0;
    this.fid = 0;
    this.ctime = 0;
    this.atime = 0;
    this.mtime = 0;
    this.major = 0x0;
    this.minor = 0x0;
    //data = new Uint8Array(0);
    this.symlink = "";
    this.mode = 0x01ED;
    this.qid = {
        type: 0, 
        version: 0, 
        path: qidnumber
    };
    //this.qid_type = 0;
    //this.qid_version = 0;
    //this.qid_path = qidnumber;
    
    //this.waswritten = false;
}

FS.prototype.CreateInode = function() {
    //console.log("CreateInode", Error().stack);
    return new Inode(++this.qidnumber);
};


FS.prototype.CreateDirectory = function(name, parentid) {
    var x = this.CreateInode();
    x.name = name;
    x.parentid = parentid;
    x.mode = 0x01FF | S_IFDIR;
    if (parentid >= 0) {
        x.uid = this.inodes[parentid].uid;
        x.gid = this.inodes[parentid].gid;
        x.mode = (this.inodes[parentid].mode & 0x1FF) | S_IFDIR;
    }
    x.qid.type = S_IFDIR >> 8;
    this.PushInode(x);
    return this.inodes.length-1;
}

FS.prototype.CreateFile = function(filename, parentid) {
    var x = this.CreateInode();
    x.name = filename;
    x.parentid = parentid;
    x.uid = this.inodes[parentid].uid;
    x.gid = this.inodes[parentid].gid;
    x.qid.type = S_IFREG >> 8;
    x.mode = (this.inodes[parentid].mode & 0x1B6) | S_IFREG;
    this.PushInode(x);
    return this.inodes.length-1;
}


FS.prototype.CreateNode = function(filename, parentid, major, minor) {
    var x = this.CreateInode();
    x.name = filename;
    x.parentid = parentid;
    x.major = major;
    x.minor = minor;
    x.uid = this.inodes[parentid].uid;
    x.gid = this.inodes[parentid].gid;
    x.qid.type = S_IFSOCK >> 8;
    x.mode = (this.inodes[parentid].mode & 0x1B6);
    this.PushInode(x);
    return this.inodes.length-1;
}
     
FS.prototype.CreateSymlink = function(filename, parentid, symlink) {
    var x = this.CreateInode();
    x.name = filename;
    x.parentid = parentid;
    x.uid = this.inodes[parentid].uid;
    x.gid = this.inodes[parentid].gid;
    x.qid.type = S_IFLNK >> 8;
    x.symlink = symlink;
    x.mode = S_IFLNK;
    this.PushInode(x);
    return this.inodes.length-1;
}

FS.prototype.CreateTextFile = function(filename, parentid, str) {
    var id = this.CreateFile(filename, parentid);
    var x = this.inodes[id];
    var data = this.inodedata[id] = new Uint8Array(str.length);
    //x.waswritten = true;
    x.size = str.length;
    for (var j in str) {
        data[j] = str.charCodeAt(j);
    }
    return id;
}

FS.prototype.OpenInode = function(id, mode) {
    var inode = this.GetInode(id);
    if ((inode.mode&S_IFMT) == S_IFDIR) {
        this.FillDirectory(id);
    }
    /*
    var type = "";
    switch(inode.mode&S_IFMT) {
        case S_IFREG: type = "File"; break;
        case S_IFBLK: type = "Block Device"; break;
        case S_IFDIR: type = "Directory"; break;
        case S_IFCHR: type = "Character Device"; break;
    }
    */
    //DebugMessage("open:" + this.GetFullPath(id) + " status:" + inode.status);
    if (inode.status == STATUS_ON_SERVER) {
        this.LoadFile(id);
        return false;
    }
    return true;
}

FS.prototype.CloseInode = function(id) {
    //DebugMessage("close: " + this.GetFullPath(id));
    var inode = this.GetInode(id);
    if (inode.status == STATUS_UNLINKED) {
        //DebugMessage("Filesystem: Delete unlinked file");
        inode.status == STATUS_INVALID;
        delete this.inodedata[id];
        //inode.waswritten = true;
        inode.size = 0;
    }
}

FS.prototype.Rename = function(olddirid, oldname, newdirid, newname) {
    //DebugMessage("Rename " + oldname + " to " + newname);
    if ((olddirid == newdirid) && (oldname == newname)) {
        return true;
    }
    var oldid = this.Search(olddirid, oldname);
    if (oldid == -1) {
        return false;
    }
    var newid = this.Search(newdirid, newname);
    if (newid != -1) {
        this.Unlink(newid);
    }

    var idx = oldid; // idx contains the id which we want to rename
    var inode = this.inodes[idx];

    // remove inode ids
    if (this.inodes[inode.parentid].firstid == idx) {
        this.inodes[inode.parentid].firstid = inode.nextid;
    } else {
        var id = this.FindPreviousID(idx);
        if (id == -1) {
            //DebugMessage("Error in Filesystem: Cannot find previous id of inode");
            abort();
        }
        this.inodes[id].nextid = inode.nextid;
    }

    inode.parentid = newdirid;
    inode.name = newname;
    inode.qid.version++;

    inode.nextid = this.inodes[inode.parentid].firstid;
    this.inodes[inode.parentid].firstid = idx;

    this.inodes[olddirid].updatedir = true;
    this.inodes[newdirid].updatedir = true;
    return true;
}

FS.prototype.Write = function(id, offset, count, GetByte) {
    var inode = this.inodes[id];
    var data = this.inodedata[id];
    //inode.waswritten = true;

    if (!data || data.length < (offset+count)) {
        this.ChangeSize(id, Math.floor(((offset+count)*3)/2) );
        inode.size = offset + count;
        data = this.inodedata[id];
    } else
    if (inode.size < (offset+count)) {
        inode.size = offset + count;
    }
    for(var i=0; i<count; i++)
        data[offset+i] = GetByte();
}

FS.prototype.Search = function(parentid, name) {
    var id = this.inodes[parentid].firstid;
    while(id != -1) {
        if (this.inodes[id].parentid != parentid) { // consistency check
            DebugMessage("Error in Filesystem: Found inode with wrong parent id");
        }
        if (this.inodes[id].name == name) return id;
        id = this.inodes[id].nextid;
    }
    return -1;
}

FS.prototype.GetTotalSize = function() {
    return 1234567;
    //var size = 0;
    //for(var i=0; i<this.inodes.length; i++) {
    //    var d = this.inodes[i].data;
    //    size += d ? d.length : 0;
    //}
    //return size;
}

FS.prototype.GetFullPath = function(idx) {
    var path = "";

    while(idx != 0) {
        path = "/" + this.inodes[idx].name + path;
        idx = this.inodes[idx].parentid;
    }
    return path.substring(1);
}

// no double linked list. So, we need this
FS.prototype.FindPreviousID = function(idx) {
    var inode = this.GetInode(idx);
    var id = this.inodes[inode.parentid].firstid;
    while(id != -1) {
        if (this.inodes[id].nextid == idx) return id;
        id = this.inodes[id].nextid;
    }
    return id;
}

FS.prototype.Unlink = function(idx) {
    if (idx == 0) return false; // root node cannot be deleted
    var inode = this.GetInode(idx);
    //DebugMessage("Unlink " + inode.name);

    // check if directory is not empty
    if ((inode.mode&S_IFMT) == S_IFDIR) {
       if (inode.firstid != -1) return false;
    }

    // update ids
    if (this.inodes[inode.parentid].firstid == idx) {
        this.inodes[inode.parentid].firstid = inode.nextid;
    } else {
        var id = this.FindPreviousID(idx);
        if (id == -1) {
            DebugMessage("Error in Filesystem: Cannot find previous id of inode");
            abort();
        }
        this.inodes[id].nextid = inode.nextid;
    }
    // don't delete the content. The file is still accessible
    this.inodes[inode.parentid].updatedir = true;
    inode.status = STATUS_UNLINKED;
    inode.nextid = -1;
    inode.firstid = -1;
    inode.parentid = -1;
    return true;
}

FS.prototype.GetInode = function(idx)
{
    if (isNaN(idx)) {
        DebugMessage("Error in filesystem: id is not a number ");
        return 0;
    }

    if ((idx < 0) || (idx > this.inodes.length)) {
        DebugMessage("Error in filesystem: Attempt to get inode with id " + idx);
        return 0;
    }
    return this.inodes[idx];
}

FS.prototype.ChangeSize = function(idx, newsize)
{
    var inode = this.GetInode(idx);
    var temp = this.inodedata[idx];
    //DebugMessage("change size to: " + newsize);
    if (newsize == inode.size) return;
    var data = this.inodedata[idx] = new Uint8Array(newsize);
    inode.size = newsize;
    //inode.waswritten = true;
    if(!temp) return;
    var size = Math.min(temp.length, inode.size);
    for(var i=0; i<size; i++) {
        data[i] = temp[i];
    }
}

FS.prototype.SearchPath = function(path) {
    //path = path.replace(/\/\//g, "/");
    path = path.replace("//", "/");
    var walk = path.split("/");
    var n = walk.length;
    if (walk[n-1].length == 0) walk.pop();
    if (walk[0].length == 0) walk.shift();
    n = walk.length;

    var parentid = 0;
    var id = -1;
    for(var i=0; i<n; i++) {
        id = this.Search(parentid, walk[i]);        
        if (id == -1) {
            if (i < n-1) return {id: -1, parentid: -1, name: walk[i]}; // one name of the path cannot be found
            return {id: -1, parentid: parentid, name: walk[i]}; // the last element in the path does not exist, but the parent
        }
        parentid = id;
    }
    return {id: id, parentid: parentid, name: walk[i]};
}
// -----------------------------------------------------

FS.prototype.GetRecursiveList = function(dirid, list) {
    var id = this.inodes[dirid].firstid;
    while(id != -1) {
        list.push(id);
        if ((this.inodes[id].mode&S_IFMT) == S_IFDIR) {
            this.GetRecursiveList(id, list);
        }
        id = this.inodes[id].nextid;
    }
}

FS.prototype.MergeFile = function(file) {
    throw "unimplemented";
    //DebugMessage("Merge path:" + file.name);
    //var ids = this.SearchPath(file.name);
    //if (ids.parentid == -1) return; // not even the path seems to exist
    //if (ids.id == -1) {
    //    ids.id = this.CreateFile(ids.name, ids.parentid); 
    //}
    //this.inodes[ids.id].data = file.data;
    //this.inodes[ids.id].size = file.data.length;
}


FS.prototype.Check = function() {
    for(var i=1; i<this.inodes.length; i++)
    {
        if (this.inodes[i].status == STATUS_INVALID) continue;
        if (this.inodes[i].nextid == i) {
            DebugMessage("Error in filesystem: file points to itself");
            abort();
        }

        var inode = this.GetInode(i);
        if (inode.parentid < 0) {
            DebugMessage("Error in filesystem: negative parent id " + i);
        }
        var n = inode.name.length;
        if (n == 0) {
            DebugMessage("Error in filesystem: inode with no name and id " + i);
        }

        for (var j in inode.name) {
            var c = inode.name.charCodeAt(j);
            if (c < 32) {
                DebugMessage("Error in filesystem: Unallowed char in filename");
            } 
        }
    }

}


FS.prototype.FillDirectory = function(dirid) {
    var inode = this.GetInode(dirid);
    if (!inode.updatedir) return;
    var parentid = inode.parentid;
    if (parentid == -1) parentid = 0; // if root directory point to the root directory

    // first get size
    var size = 0;
    var id = this.inodes[dirid].firstid;
    while(id != -1) {
        size += 13 + 8 + 1 + 2 + UTF8Length(this.inodes[id].name);
        id = this.inodes[id].nextid;
    }

    size += 13 + 8 + 1 + 2 + 1; // "." entry
    size += 13 + 8 + 1 + 2 + 2; // ".." entry
    //DebugMessage("size of dir entry: " + size);
    var data = this.inodedata[dirid] = new Uint8Array(size);
    //inode.waswritten = true;
    inode.size = size;

    var offset = 0x0;
    offset += Marshall(
        ["Q", "d", "b", "s"],
        [this.MakeQid(this.inodes[dirid]), 
        offset+13+8+1+2+1, 
        this.inodes[dirid].mode >> 12, 
        "."],
        data, offset);

    offset += Marshall(
        ["Q", "d", "b", "s"],
        [this.MakeQid(this.inodes[parentid]),
        offset+13+8+1+2+2, 
        this.inodes[parentid].mode >> 12, 
        ".."],
        data, offset);

    id = this.inodes[dirid].firstid;
    while(id != -1) {
        offset += Marshall(
        ["Q", "d", "b", "s"],
        [this.MakeQid(this.inodes[id]),
        offset+13+8+1+2+UTF8Length(this.inodes[id].name),
        this.inodes[id].mode >> 12,
        this.inodes[id].name],
        data, offset);
        id = this.inodes[id].nextid;
    }
    inode.updatedir = false;
}


// -----------------------------------------------------

// only support for security.capabilities
// should return a  "struct vfs_cap_data" defined in
// linux/capability for format
// check also:
//   sys/capability.h
//   http://lxr.free-electrons.com/source/security/commoncap.c#L376
//   http://man7.org/linux/man-pages/man7/capabilities.7.html
//   http://man7.org/linux/man-pages/man8/getcap.8.html
//   http://man7.org/linux/man-pages/man3/libcap.3.html
FS.prototype.PrepareCAPs = function(id) {
    var inode = this.GetInode(id);
    if (inode.caps) return inode.caps.length;
    inode.caps = new Uint8Array(12);
    // format is little endian
    // magic_etc (revision=0x01: 12 bytes)
    inode.caps[0]  = 0x00;
    inode.caps[1]  = 0x00;
    inode.caps[2]  = 0x00;
    inode.caps[3]  = 0x01;
    // permitted (full capabilities)
    inode.caps[4]  = 0xFF;
    inode.caps[5]  = 0xFF;
    inode.caps[6]  = 0xFF;
    inode.caps[7]  = 0xFF;
    // inheritable (full capabilities
    inode.caps[8]  = 0xFF;
    inode.caps[9]  = 0xFF;
    inode.caps[10] = 0xFF;
    inode.caps[11] = 0xFF;

    return inode.caps.length;
}

//FS.prototype.ClearCache = function()
//{
//    for(var id in this.inodedata)
//    {
//        if(!this.inodes[id].waswritten)
//        {
//            delete this.inodedata[id];
//        }
//    }
//};

FS.prototype.MakeQid = function(inode)
{
    return inode.qid;
    //return {
    //    type: inode.qid_type, 
    //    version: inode.qid_version, 
    //    path: inode.qid_path,
    //};
};