概述

Termux是一个Android下一个高级的终端模拟器，开源且不需要root，支持apt管理软件包，拥有自己的apt仓库源，可以十分方便地安装软件包，可以实现支持Python,PHP,Ruby,Go,Nodejs,MySQL等功能环境。

一切皆文件

linux/unix下的哲学核心思想是一切皆文件。它指的是，对所有文件（目录、字符设备、块设备、套接字、打印机、进程、线程、管道等）操作，读写都可用fopen()/fclose()/fwrite()/fread()等函数进行处理，屏蔽了硬件的区别，所有设备都抽象成文件，提供统一的接口给用户，虽然类型各不相同，但是对其提供的却是同一套操作界面，更进一步，对文件的操作也可以跨文件系统执行。

操作一个已经打开的文件：使用文件描述符（file descriptor），简称fd，它是一个对应某个已经打开的文件的索引（非负整数）。

文件描述符

文件描述符在形式上是一个非负整数。实际上，它是一个索引值，指向内核为每一个进程所维护的该进程打开文件的记录表。当程序打开一个现有文件或者创建一个新文件时，内核向进程返回一个文件描述符。在程序设计中，一些涉及底层的程序编写往往会围绕着文件描述符展开。

Linux 系统中，把一切都看做是文件，当进程打开现有文件或创建新文件时，内核向进程返回一个文件描述符，文件描述符就是内核为了高效管理已被打开的文件所创建的索引，用来指向被打开的文件，所有执行I/O操作的系统调用都会通过文件描述符。

修改包名

主要是指定目录的前缀.

Termux修改包名

源码解读

流程图:

setupIfNeeded

bootstraps.zip目录结构：

bootstrap-aarch64
    ├── SYMLINKS.txt
    ├── bin
    ├── etc
    ├── include
    ├── lib
    ├── libexec
    ├── repo.asc
    ├── share
    ├── tmp
    └── var

public static void setupIfNeeded(final Activity activity, final Runnable whenDone) {
    // Termux can only be run as the primary user (device owner) since only that
    // account has the expected file system paths. Verify that:
    UserManager um = (UserManager) activity.getSystemService(Context.USER_SERVICE);
    boolean isPrimaryUser = um.getSerialNumberForUser(android.os.Process.myUserHandle()) == 0;
    if (!isPrimaryUser) {
        Termux.mInstance.setInstalled(false);
        Termux.mInstance.getTermuxHandle().initFail();
        return;
    }

    final File PREFIX_FILE = new File(Termux.PREFIX_PATH);
    if (PREFIX_FILE.isDirectory()) {
        whenDone.run();
        return;
    }

    new Thread() {
        @Override
        public void run() {
            try {
                final String STAGING_PREFIX_PATH = Termux.FILES_PATH + "/usr-staging";
                final File STAGING_PREFIX_FILE = new File(STAGING_PREFIX_PATH);

                if (STAGING_PREFIX_FILE.exists()) {
                    deleteFolder(STAGING_PREFIX_FILE);
                }

                final byte[] buffer = new byte[8096];
                final List<Pair<String, String>> symlinks = new ArrayList<>(50);

                final URL zipUrl = determineZipUrl();
                try (ZipInputStream zipInput = new ZipInputStream(zipUrl.openStream())) {
                    ZipEntry zipEntry;
                    while ((zipEntry = zipInput.getNextEntry()) != null) {
                        if (zipEntry.getName().equals("SYMLINKS.txt")) {
                            BufferedReader symlinksReader = new BufferedReader(new InputStreamReader(zipInput));
                            String line;
                            while ((line = symlinksReader.readLine()) != null) {
                                String[] parts = line.split("←");
                                if (parts.length != 2)
                                    throw new RuntimeException("Malformed symlink line: " + line);
                                String oldPath = parts[0];
                                String newPath = STAGING_PREFIX_PATH + "/" + parts[1];
                                symlinks.add(Pair.create(oldPath, newPath));

                                ensureDirectoryExists(new File(newPath).getParentFile());
                            }
                        } else {
                            String zipEntryName = zipEntry.getName();
                            File targetFile = new File(STAGING_PREFIX_PATH, zipEntryName);
                            boolean isDirectory = zipEntry.isDirectory();

                            ensureDirectoryExists(isDirectory ? targetFile : targetFile.getParentFile());

                            if (!isDirectory) {
                                try (FileOutputStream outStream = new FileOutputStream(targetFile)) {
                                    int readBytes;
                                    while ((readBytes = zipInput.read(buffer)) != -1)
                                        outStream.write(buffer, 0, readBytes);
                                }
                                if (zipEntryName.startsWith("bin/") || zipEntryName.startsWith("libexec") || zipEntryName.startsWith("lib/apt/methods")) {
                                    //noinspection OctalInteger
                                    Os.chmod(targetFile.getAbsolutePath(), 0700);
                                }
                            }
                        }
                    }
                }

                if (symlinks.isEmpty())
                    throw new RuntimeException("No SYMLINKS.txt encountered");
                for (Pair<String, String> symlink : symlinks) {
                    Os.symlink(symlink.first, symlink.second);
                }

                if (!STAGING_PREFIX_FILE.renameTo(PREFIX_FILE)) {
                    throw new RuntimeException("Unable to rename staging folder");
                }
                activity.runOnUiThread(whenDone);
            } catch (final Exception e) {
                Log.e(EmulatorDebug.LOG_TAG, "Bootstrap error", e);
                Termux.mInstance.setInstalled(false);
                Termux.mInstance.getTermuxHandle().initFail();
            }
        }
    }.start();
}

private static void ensureDirectoryExists(File directory) {
    if (!directory.isDirectory() && !directory.mkdirs()) {
        throw new RuntimeException("Unable to create directory: " + directory.getAbsolutePath());
    }
}

/**
    * Get bootstrap zip url for this systems cpu architecture.
    */
private static URL determineZipUrl() throws MalformedURLException {
    String archName = determineTermuxArchName();
    String url = Build.VERSION.SDK_INT >= Build.VERSION_CODES.N
            ? "https://termux.org/bootstrap-" + archName + ".zip"
            : "https://termux.net/bootstrap/bootstrap-" + archName + ".zip";
    return new URL(url);
}

private static String determineTermuxArchName() {
    // Note that we cannot use System.getProperty("os.arch") since that may give e.g. "aarch64"
    // while a 64-bit runtime may not be installed (like on the Samsung Galaxy S5 Neo).
    // Instead we search through the supported abi:s on the device, see:
    // http://developer.android.com/ndk/guides/abis.html
    // Note that we search for abi:s in preferred order (the ordering of the
    // Build.SUPPORTED_ABIS list) to avoid e.g. installing arm on an x86 system where arm
    // emulation is available.
    for (String androidArch : Build.SUPPORTED_ABIS) {
        switch (androidArch) {
            case "arm64-v8a":
                return "aarch64";
            case "armeabi-v7a":
                return "arm";
            case "x86_64":
                return "x86_64";
            case "x86":
                return "i686";
        }
    }
    throw new RuntimeException("Unable to determine arch from Build.SUPPORTED_ABIS =  " +
            Arrays.toString(Build.SUPPORTED_ABIS));
}

createSubprocess

static int create_subprocess(JNIEnv* env,
        char const* cmd,
        char const* cwd,
        char* const argv[],
        char** envp,
        int* pProcessId,
        jint rows,
        jint columns)
{
    int ptm = open("/dev/ptmx", O_RDWR | O_CLOEXEC);
    if (ptm < 0) return throw_runtime_exception(env, "Cannot open /dev/ptmx");

#ifdef LACKS_PTSNAME_R
    char* devname;
#else
    char devname[64];
#endif
    if (grantpt(ptm) || unlockpt(ptm) ||
#ifdef LACKS_PTSNAME_R
            (devname = ptsname(ptm)) == NULL
#else
            ptsname_r(ptm, devname, sizeof(devname))
#endif
       ) {
        return throw_runtime_exception(env, "Cannot grantpt()/unlockpt()/ptsname_r() on /dev/ptmx");
    }

    // Enable UTF-8 mode and disable flow control to prevent Ctrl+S from locking up the display.
    struct termios tios;
    tcgetattr(ptm, &tios);
    tios.c_iflag |= IUTF8;
    tios.c_iflag &= ~(IXON | IXOFF);
    tcsetattr(ptm, TCSANOW, &tios);

    /** Set initial winsize. */
    struct winsize sz = { .ws_row = (unsigned short) rows, .ws_col = (unsigned short) columns };
    ioctl(ptm, TIOCSWINSZ, &sz);

    pid_t pid = fork();
    if (pid < 0) {
        return throw_runtime_exception(env, "Fork failed");
    } else if (pid > 0) {
        *pProcessId = (int) pid;
        return ptm;
    } else {
        // Clear signals which the Android java process may have blocked:
        sigset_t signals_to_unblock;
        sigfillset(&signals_to_unblock);
        sigprocmask(SIG_UNBLOCK, &signals_to_unblock, 0);

        close(ptm);
        setsid();

        int pts = open(devname, O_RDWR);
        if (pts < 0) exit(-1);

        dup2(pts, 0);
        dup2(pts, 1);
        dup2(pts, 2);

        DIR* self_dir = opendir("/proc/self/fd");
        if (self_dir != NULL) {
            int self_dir_fd = dirfd(self_dir);
            struct dirent* entry;
            while ((entry = readdir(self_dir)) != NULL) {
                int fd = atoi(entry->d_name);
                if(fd > 2 && fd != self_dir_fd) close(fd);
            }
            closedir(self_dir);
        }

        clearenv();
        if (envp) for (; *envp; ++envp) putenv(*envp);

        if (chdir(cwd) != 0) {
            char* error_message;
            // No need to free asprintf()-allocated memory since doing execvp() or exit() below.
            if (asprintf(&error_message, "chdir(\"%s\")", cwd) == -1) error_message = "chdir()";
            perror(error_message);
            fflush(stderr);
        }
        execvp(cmd, argv);
        // Show terminal output about failing exec() call:
        char* error_message;
        if (asprintf(&error_message, "exec(\"%s\")", cmd) == -1) error_message = "exec()";
        perror(error_message);
        _exit(1);
    }
}

操作terminal

/**
    * A queue written to from a separate thread when the process outputs, and read by main thread to process by
    * terminal emulator.
    */
private final ByteQueue mProcessToTerminalIOQueue = new ByteQueue(4096);
/**
    * A queue written to from the main thread due to user interaction, and read by another thread which forwards by
    * writing to the {@link #mTerminalFileDescriptor}.
    */
private final ByteQueue mTerminalToProcessIOQueue = new ByteQueue(4096);

public void initializeEmulator(int columns, int rows) {

    int[] processId = new int[1];
    mTerminalFileDescriptor = JNI.createSubprocess(mShellPath, mCwd, mArgs, mEnv, processId, rows, columns);
    mShellPid = processId[0];

    final FileDescriptor terminalFileDescriptorWrapped = wrapFileDescriptor(mTerminalFileDescriptor);

    new Thread("TermSessionInputReader[pid=" + mShellPid + "]") {
        @Override
        public void run() {
            try (InputStream termIn = new FileInputStream(terminalFileDescriptorWrapped)) {
                final byte[] buffer = new byte[4096];
                while (true) {
                    int read = termIn.read(buffer);
                    if (read == -1) return;
                    if (!mProcessToTerminalIOQueue.write(buffer, 0, read)) return;
                    mMainThreadHandler.sendEmptyMessage(MSG_NEW_INPUT);
                }
            } catch (Exception e) {
                // Ignore, just shutting down.
            }
        }
    }.start();

    new Thread("TermSessionOutputWriter[pid=" + mShellPid + "]") {
        @Override
        public void run() {
            final byte[] buffer = new byte[4096];
            try (FileOutputStream termOut = new FileOutputStream(terminalFileDescriptorWrapped)) {
                while (true) {
                    int bytesToWrite = mTerminalToProcessIOQueue.read(buffer, true);
                    if (bytesToWrite == -1) return;
                    termOut.write(buffer, 0, bytesToWrite);
                }
            } catch (IOException e) {
                // Ignore.
            }
        }
    }.start();

    new Thread("TermSessionWaiter[pid=" + mShellPid + "]") {
        @Override
        public void run() {
            int processExitCode = JNI.waitFor(mShellPid);
            mMainThreadHandler.sendMessage(mMainThreadHandler.obtainMessage(MSG_PROCESS_EXITED, processExitCode));
        }
    }.start();

}

参数

mShellPath: /data/data/$pkg/files/usr/bin/login
mCwd: /data/data/$pkg/files/home
mArgs: [-login]
mEnv: [TERM=xterm-256color, HOME=/data/data/$pkg/files/home, PREFIX=/data/data/$pkg/files/usr, BOOTCLASSPATH/system/framework/com.qualcomm.qti.camera.jar:/system/framework/QPerformance.jar:/system/framework/core-oj.jar:/system/framework/core-libart.jar:/system/framework/conscrypt.jar:/system/framework/okhttp.jar:/system/framework/bouncycastle.jar:/system/framework/apache-xml.jar:/system/framework/legacy-test.jar:/system/framework/ext.jar:/system/framework/framework.jar:/system/framework/telephony-common.jar:/system/framework/voip-common.jar:/system/framework/ims-common.jar:/system/framework/org.apache.http.legacy.boot.jar:/system/framework/android.hidl.base-V1.0-java.jar:/system/framework/android.hidl.manager-V1.0-java.jar:/system/framework/tcmiface.jar:/system/framework/WfdCommon.jar:/system/framework/oem-services.jar:/system/framework/qcom.fmradio.jar:/system/framework/telephony-ext.jar:/system/app/miui/miui.apk:/system/app/miuisystem/miuisystem.apk, ANDROID_ROOT=/system, ANDROID_DATA=/data, EXTERNAL_STORAGE=/sdcard, LD_LIBRARY_PATH=/data/data/$pkg/files/usr/lib, LANG=en_US.UTF-8, PATH=/data/data/$pkg/files/usr/bin:/data/data/$pkg/files/usr/bin/applets, PWD=/data/data/$pkg/files/home, TMPDIR=/data/data/$pkg/files/usr/tmp]
mShellPid: 15381
mTerminalFileDescriptor: 54

苍耳的博客

Termux解析

概述