diagnose_usb.cpp

/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "diagnose_usb.h"

#include <errno.h>
#include <unistd.h>

#include <string>

#include <android-base/stringprintf.h>

#if defined(__linux__)
#include <grp.h>
#include <pwd.h>
#endif

static const char kPermissionsHelpUrl[] = "http://developer.android.com/tools/device.html";

// Returns a message describing any potential problems we find with udev, or an empty string if we
// can't find plugdev information (i.e. udev is not installed).
static std::string GetUdevProblem() {
#if defined(__linux__)
    errno = 0;
    group* plugdev_group = getgrnam("plugdev");

    if (plugdev_group == nullptr) {
        if (errno != 0) {
            perror("failed to read plugdev group info");
        }
        // We can't give any generally useful advice here, just let the caller print the help URL.
        return "";
    }

    // getgroups(2) indicates that the GNU group_member(3) may not check the egid so we check it
    // additionally just to be sure.
    if (group_member(plugdev_group->gr_gid) || getegid() == plugdev_group->gr_gid) {
        // The user is in plugdev so the problem is likely with the udev rules.
        return "user in plugdev group; are your udev rules wrong?";
    }
    passwd* pwd = getpwuid(getuid());
    return android::base::StringPrintf("user %s is not in the plugdev group",
                                       pwd ? pwd->pw_name : "?");
#else
    return "";
#endif
}

// Short help text must be a single line, and will look something like:
//
//   no permissions (reason); see [URL]
std::string UsbNoPermissionsShortHelpText() {
    std::string help_text = "no permissions";

    std::string problem(GetUdevProblem());
    if (!problem.empty()) help_text += " (" + problem + ")";

    return android::base::StringPrintf("%s; see [%s]", help_text.c_str(), kPermissionsHelpUrl);
}

// Long help text can span multiple lines but doesn't currently provide more detailed information:
//
//   insufficient permissions for device: reason
//   See [URL] for more information
std::string UsbNoPermissionsLongHelpText() {
    std::string header = "insufficient permissions for device";

    std::string problem(GetUdevProblem());
    if (!problem.empty()) header += ": " + problem;

    return android::base::StringPrintf("%s\nSee [%s] for more information", header.c_str(),
                                       kPermissionsHelpUrl);
}