Merge "Add "dmctl uuid" command"

fs_mgr/libdm/dm.cpp

@@ -427,6 +427,20 @@ bool DeviceMapper::GetDmDevicePathByName(const std::string& name, std::string* p
     return true;
 }
 
+// Accepts a device mapper device name (like system_a, vendor_b etc) and
+// returns its UUID.
+bool DeviceMapper::GetDmDeviceUUIDByName(const std::string& name, std::string* uuid) {
+    struct dm_ioctl io;
+    InitIo(&io, name);
+    if (ioctl(fd_, DM_DEV_STATUS, &io) < 0) {
+        PLOG(WARNING) << "DM_DEV_STATUS failed for " << name;
+        return false;
+    }
+
+    *uuid = std::string(io.uuid);
+    return true;
+}
+
 bool DeviceMapper::GetDeviceNumber(const std::string& name, dev_t* dev) {
     struct dm_ioctl io;
     InitIo(&io, name);

fs_mgr/libdm/include/libdm/dm.h

@@ -172,6 +172,13 @@ class DeviceMapper final {
     // could race with ueventd.
     bool GetDmDevicePathByName(const std::string& name, std::string* path);
 
+    // Returns the device mapper UUID for a given name.  If the device does not
+    // exist, false is returned, and the path parameter is not set.
+    //
+    // WaitForFile() should not be used in conjunction with this call, since it
+    // could race with ueventd.
+    bool GetDmDeviceUUIDByName(const std::string& name, std::string* path);
+
     // Returns a device's unique path as generated by ueventd. This will return
     // true as long as the device has been created, even if ueventd has not
     // processed it yet.

fs_mgr/tools/dmctl.cpp

@@ -49,6 +49,7 @@ static int Usage(void) {
     std::cerr << "  delete <dm-name>" << std::endl;
     std::cerr << "  list <devices | targets> [-v]" << std::endl;
     std::cerr << "  getpath <dm-name>" << std::endl;
+    std::cerr << "  getuuid <dm-name>" << std::endl;
     std::cerr << "  info <dm-name>" << std::endl;
     std::cerr << "  status <dm-name>" << std::endl;
     std::cerr << "  resume <dm-name>" << std::endl;
@@ -391,6 +392,22 @@ static int GetPathCmdHandler(int argc, char** argv) {
     return 0;
 }
 
+static int GetUUIDCmdHandler(int argc, char** argv) {
+    if (argc != 1) {
+        std::cerr << "Invalid arguments, see \'dmctl help\'" << std::endl;
+        return -EINVAL;
+    }
+
+    DeviceMapper& dm = DeviceMapper::Instance();
+    std::string uuid;
+    if (!dm.GetDmDeviceUUIDByName(argv[0], &uuid)) {
+        std::cerr << "Could not query uuid of device \"" << argv[0] << "\"." << std::endl;
+        return -EINVAL;
+    }
+    std::cout << uuid << std::endl;
+    return 0;
+}
+
 static int InfoCmdHandler(int argc, char** argv) {
     if (argc != 1) {
         std::cerr << "Invalid arguments, see \'dmctl help\'" << std::endl;
@@ -504,6 +521,7 @@ static std::map<std::string, std::function<int(int, char**)>> cmdmap = {
         {"list", DmListCmdHandler},
         {"help", HelpCmdHandler},
         {"getpath", GetPathCmdHandler},
+        {"getuuid", GetUUIDCmdHandler},
         {"info", InfoCmdHandler},
         {"table", TableCmdHandler},
         {"status", StatusCmdHandler},