feat: custom distro root filesystem type and mount options

localization/strings/en-US/Resources.resw

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <root>
   <!--
     Microsoft ResX Schema
@@ -453,6 +453,13 @@ Arguments for managing Windows Subsystem for Linux:
             --from-file &lt;Path&gt;
                 Install a distribution from a local file.
 
+            --fs-type &lt;FsType&gt;
+                Specify the filesystem type to use for the distribution root.
+                Defaults to ext4.
+
+            --fs-mount-options &lt;Options&gt;
+                Specify additional mount options for the filesystem.
+
             --legacy
                 Use the legacy distribution manifest.
 
@@ -493,6 +500,9 @@ Arguments for managing Windows Subsystem for Linux:
             --resize &lt;MemoryString&gt;
                 Resize the disk of the distribution to the specified size.
 
+            --set-fs-mount-options &lt;Options&gt;
+                Set the filesystem mount options for the distribution root.
+
     --mount &lt;Disk&gt;
         Attaches and mounts a physical or virtual disk in all WSL 2 distributions.
 
@@ -568,6 +578,13 @@ Arguments for managing distributions in Windows Subsystem for Linux:
                 Specifies that the provided file is a .vhd or .vhdx file, not a tar file.
                 This operation makes a copy of the VHD file at the specified install location.
 
+            --fs-type &lt;FsType&gt;
+                Specify the filesystem type to use for the distribution root.
+                Defaults to ext4.
+
+            --fs-mount-options &lt;Options&gt;
+                Specify additional mount options for the filesystem.
+
     --import-in-place &lt;Distro&gt; &lt;FileName&gt;
         Imports the specified VHD file as a new distribution.
         This virtual hard disk must be formatted with the ext4 filesystem type.
@@ -608,10 +625,10 @@ Arguments for managing distributions in Windows Subsystem for Linux:
 "}{Locked="--debug-shell
 "}{Locked="--install "}{Locked="--list "}{Locked="--online'"}{Locked="--enable-wsl1
 "}{Locked="--fixed-vhd
-"}{Locked="--from-file "}{Locked="--legacy
+"}{Locked="--from-file "}{Locked="--fs-type "}{Locked="--fs-mount-options "}{Locked="--legacy
 "}{Locked="--location "}{Locked="--name "}{Locked="--no-distribution
 "}{Locked="--no-launch,"}{Locked="--version "}{Locked="--vhd-size "}{Locked="--web-download
-"}{Locked="--manage "}{Locked="--move "}{Locked="--set-sparse,"}{Locked="--set-default-user "}{Locked="--resize "}{Locked="--mount "}{Locked="--vhd
+"}{Locked="--manage "}{Locked="--move "}{Locked="--set-sparse,"}{Locked="--set-default-user "}{Locked="--resize "}{Locked="--set-fs-mount-options "}{Locked="--mount "}{Locked="--vhd
 "}{Locked="--bare
 "}{Locked="--name "}{Locked="--type "}{Locked="--options "}{Locked="--partition "}{Locked="--set-default-version "}{Locked="--shutdown
 "}{Locked="--force
@@ -1082,8 +1099,8 @@ Falling back to NAT networking.</value>
     <value>The distribution failed to start. Error code: {}, failure step: {}</value>
     <comment>{FixedPlaceholder="{}"}Command line arguments, file names and string inserts should not be translated</comment>
   </data>
-  <data name="MessageDiskCorrupted" xml:space="preserve">
-    <value>The distribution failed to start because its virtual disk is corrupted.</value>
+  <data name="MessageMountFailed" xml:space="preserve">
+    <value>The distribution failed to start because its virtual disk is corrupted, has an unexpected filesystem type, or has invalid mount options.</value>
   </data>
   <data name="MessageConfigKeyDuplicated" xml:space="preserve">
     <value>Duplicated config key '{}' in {}:{} (Conflicting key: '{}' in {}:{})</value>

src/linux/init/main.cpp

@@ -65,6 +65,9 @@ Module Name:
 #include "SocketChannel.h"
 
 #define BSDTAR_PATH "/usr/bin/bsdtar"
+#define BTRFS_CREATE_ARG "create"
+#define BTRFS_PATH "/usr/sbin/btrfs"
+#define BTRFS_SUBVOLUME_ARG "subvolume"
 #define BINFMT_REGISTER_STRING ":" LX_INIT_BINFMT_NAME ":M::MZ::" LX_INIT_PATH ":FP\n"
 #define BINFMT_PATH PROCFS_PATH "/sys/fs/binfmt_misc"
 #define CHRONY_CONF_PATH ETC_PATH "/chrony.conf"
@@ -136,7 +139,8 @@ int EnableInterface(int Socket, const char* Name);
 
 int ExportToSocket(const char* Source, int Socket, int ErrorSocket, unsigned int flags);
 
-int FormatDevice(unsigned int Lun);
+int FormatDevice(unsigned int Lun, const char* FsType);
+int CreateBtrfsSubvolumeOnDevice(unsigned int Lun, const char* MountOptions);
 
 std::string GetLunDeviceName(unsigned int Lun);
 
@@ -875,19 +879,23 @@ Return Value:
     return Result;
 }
 
-int FormatDevice(unsigned int Lun)
+int FormatDevice(unsigned int Lun, const char* FsType)
 
 /*++
 
 Routine Description:
 
-    This routine formats the specified SCSI device with the ext4 file system.
-    N.B. The group size was chosen based on the best practices for Linux VHDs:
+    This routine formats the specified SCSI device with the <FsType> file system.
+
+    N.B. The ext4 group size was chosen based on the best practices for Linux VHDs:
          https://docs.microsoft.com/en-us/windows-server/virtualization/hyper-v/best-practices-for-running-linux-on-hyper-v
 
+    N.B. The xfs data section options (-d) are also determined based on the VHD sector size of 1MB, as suggested in the link above.
+
 Arguments:
 
     Lun - Supplies the LUN number of the SCSI device.
+    FsType - The filesystem type to format the device with.
 
 Return Value:
 
@@ -901,7 +909,30 @@ try
 
     WaitForBlockDevice(DevicePath.c_str());
 
-    std::string CommandLine = std::format("/usr/sbin/mkfs.ext4 -G 4096 '{}'", DevicePath);
+    if (FsType == nullptr)
+    {
+        FsType = "ext4";
+    }
+
+    std::string CommandLine;
+    if (strcmp(FsType, "ext4") == 0)
+    {
+        CommandLine = std::format("/usr/sbin/mkfs.ext4 -G 4096 '{}'", DevicePath);
+    }
+    else if (strcmp(FsType, "btrfs") == 0)
+    {
+        CommandLine = std::format("/usr/sbin/mkfs.btrfs '{}'", DevicePath);
+    }
+    else if (strcmp(FsType, "xfs") == 0)
+    {
+        CommandLine = std::format("/usr/sbin/mkfs.xfs -s size=4096 -d su=1m,sw=1 '{}'", DevicePath);
+    }
+    else
+    {
+        LOG_ERROR("Unsupported filesystem type: {}", FsType);
+        errno = ENOSYS;
+        return -1;
+    }
     if (UtilExecCommandLine(CommandLine.c_str(), nullptr) < 0)
     {
         return -1;
@@ -911,6 +942,84 @@ try
 }
 CATCH_RETURN_ERRNO()
 
+int CreateBtrfsSubvolumeOnDevice(unsigned int Lun, const char* MountOptions)
+/*++
+    This routine creates a btrfs subvolume on the specified SCSI device.
+    It is a no-op if there is no subvolume name in the mount options or
+    the subvolume already exists.
+
+Arguments:
+
+    Lun - Supplies the LUN number of the SCSI device.
+    MountOptions - The mount options to use when mounting the device.
+        The subvolume name is extracted from these options.
+
+Return Value:
+
+    0 on success, < 0 on failure.
+--*/
+try
+{
+    if (MountOptions == nullptr)
+    {
+        return 0;
+    }
+
+    std::string_view options(MountOptions);
+    std::string_view subvolName;
+
+    size_t pos = 0;
+    while (pos < options.size())
+    {
+        size_t end = options.find(',', pos);
+        if (end == std::string_view::npos)
+        {
+            end = options.size();
+        }
+
+        std::string_view option = options.substr(pos, end - pos);
+        if (option.starts_with("subvol="))
+        {
+            subvolName = option.substr(7); // Skip "subvol="
+            break;
+        }
+
+        pos = end + 1;
+    }
+
+    if (subvolName.empty())
+    {
+        return 0;
+    }
+
+    std::string DevicePath = GetLunDevicePath(Lun);
+    std::string TempMountPath;
+    THROW_LAST_ERROR_IF(CreateTempDirectory("/tmp", TempMountPath) < 0);
+
+    auto unmountOnExit = wil::scope_exit([&TempMountPath]() {
+        umount(TempMountPath.c_str());
+        rmdir(TempMountPath.c_str());
+    });
+
+    THROW_LAST_ERROR_IF(UtilMount(DevicePath.c_str(), TempMountPath.c_str(), "btrfs", 0, nullptr, c_defaultRetryTimeout) < 0);
+
+    std::string SubvolPath = std::format("{}/{}", TempMountPath, subvolName);
+
+    struct stat st;
+    if (stat(SubvolPath.c_str(), &st) == 0)
+    {
+        return 0;
+    }
+
+    THROW_LAST_ERROR_IF(errno != ENOENT);
+
+    const char* Argv[] = {BTRFS_PATH, BTRFS_SUBVOLUME_ARG, BTRFS_CREATE_ARG, SubvolPath.c_str(), nullptr};
+    THROW_LAST_ERROR_IF(UtilCreateProcessAndWait(Argv[0], Argv) < 0);
+
+    return 0;
+}
+CATCH_RETURN_ERRNO()
+
 std::string GetLunDeviceName(unsigned int Lun)
 
 /*++
@@ -2701,13 +2810,20 @@ void ProcessImportExportMessage(gsl::span<gsl::byte> Buffer, wsl::shared::Socket
             ListenSocket = UtilListenVsockAnyPort(&ListenAddress, 2, true);
             THROW_LAST_ERROR_IF(!ListenSocket);
 
+            auto* FsType = wsl::shared::string::FromSpan(Buffer, Message->FsTypeOffset);
+            auto* MountOptions = wsl::shared::string::FromSpan(Buffer, Message->MountOptionsOffset);
+
             if (Message->Header.MessageType == LxMiniInitMessageImport)
             {
-                THROW_LAST_ERROR_IF(FormatDevice(Message->DeviceId) < 0);
+                THROW_LAST_ERROR_IF(FormatDevice(Message->DeviceId, FsType) < 0);
+
+                if (FsType != nullptr && strcmp(FsType, "btrfs") == 0)
+                {
+                    // create the subvolume if specified in mount options
+                    THROW_LAST_ERROR_IF(CreateBtrfsSubvolumeOnDevice(Message->DeviceId, MountOptions) < 0);
+                }
             }
 
-            auto* FsType = wsl::shared::string::FromSpan(Buffer, Message->FsTypeOffset);
-            auto* MountOptions = wsl::shared::string::FromSpan(Buffer, Message->MountOptionsOffset);
             THROW_LAST_ERROR_IF(MountDevice(Message->MountDeviceType, Message->DeviceId, DISTRO_PATH, FsType, Message->Flags, MountOptions) < 0);
 
             Result = 0;

src/windows/common/WslClient.cpp

@@ -313,12 +313,16 @@ int ImportDistribution(_In_ std::wstring_view commandLine)
     std::filesystem::path filePath;
     ULONG flags = LXSS_IMPORT_DISTRO_FLAGS_NO_OOBE;
     DWORD version = LXSS_WSL_VERSION_DEFAULT;
+    std::optional<std::wstring> fsType;
+    std::optional<std::wstring> fsMountOptions;
 
     parser.AddPositionalArgument(name, 0);
     parser.AddPositionalArgument(AbsolutePath(installPath), 1);
     parser.AddPositionalArgument(filePath, 2);
     parser.AddArgument(WslVersion(version), WSL_IMPORT_ARG_VERSION);
     parser.AddArgument(SetFlag<LXSS_IMPORT_DISTRO_FLAGS_VHD, ULONG>{flags}, WSL_IMPORT_ARG_VHD);
+    parser.AddArgument(fsType, WSL_IMPORT_ARG_FS_TYPE);
+    parser.AddArgument(fsMountOptions, WSL_IMPORT_ARG_FS_MOUNT_OPTIONS);
 
     parser.Parse();
 
@@ -379,7 +383,15 @@ int ImportDistribution(_In_ std::wstring_view commandLine)
     {
         wsl::windows::common::HandleConsoleProgressBar progressBar(fileHandle, Localization::MessageImportProgress());
         wsl::windows::common::SvcComm service;
-        service.RegisterDistribution(name, version, fileHandle, installPath->c_str(), flags);
+        service.RegisterDistribution(
+            name,
+            version,
+            fileHandle,
+            installPath->c_str(),
+            flags,
+            std::nullopt,
+            fsType.has_value() ? fsType->c_str() : nullptr,
+            fsMountOptions.has_value() ? fsMountOptions->c_str() : nullptr);
     }
 
     directory_cleanup.release();
@@ -452,6 +464,8 @@ int Install(_In_ std::wstring_view commandLine)
     bool noDistribution = false;
     bool legacy = false;
     bool webDownload = IsWindowsServer();
+    std::optional<std::wstring> fsType;
+    std::optional<std::wstring> fsMountOptions;
 
     ArgumentParser parser(std::wstring{commandLine}, WSL_BINARY_NAME);
     parser.AddPositionalArgument(distroArgument, 0);
@@ -469,6 +483,8 @@ int Install(_In_ std::wstring_view commandLine)
     parser.AddArgument(g_promptBeforeExit, WSL_INSTALL_ARG_PROMPT_BEFORE_EXIT_OPTION);
     parser.AddArgument(SizeString(vhdSize), WSL_INSTALL_ARG_VHD_SIZE);
     parser.AddArgument(fixedVhd, WSL_INSTALL_ARG_FIXED_VHD);
+    parser.AddArgument(fsType, WSL_INSTALL_ARG_FS_TYPE);
+    parser.AddArgument(fsMountOptions, WSL_INSTALL_ARG_FS_MOUNT_OPTIONS);
 
     parser.Parse();
 
@@ -525,7 +541,9 @@ int Install(_In_ std::wstring_view commandLine)
             file,
             location.has_value() ? location->c_str() : nullptr,
             fixedVhd ? LXSS_IMPORT_DISTRO_FLAGS_FIXED_VHD : 0,
-            vhdSize);
+            vhdSize,
+            fsType.has_value() ? fsType->c_str() : nullptr,
+            fsMountOptions.has_value() ? fsMountOptions->c_str() : nullptr);
 
         wsl::windows::common::wslutil::PrintMessage(Localization::MessageDistributionInstalled(installedName.get()), stdout);
 
@@ -551,7 +569,7 @@ int Install(_In_ std::wstring_view commandLine)
     if (!noDistribution && (legacy || !rebootRequired))
     {
         auto result = WslInstall::InstallDistribution(
-            installResult, distroArgument, version, !noLaunchAfterInstall, webDownload, legacy, fixedVhd, name, location, vhdSize);
+            installResult, distroArgument, version, !noLaunchAfterInstall, webDownload, legacy, fixedVhd, name, location, vhdSize, fsType, fsMountOptions);
 
         std::optional<std::wstring> flavor;
         if (installResult.Distribution.has_value())
@@ -887,6 +905,7 @@ int Manage(_In_ std::wstring_view commandLine)
     std::optional<std::wstring> move;
     std::optional<std::wstring> defaultUser;
     std::optional<uint64_t> resize;
+    std::optional<std::wstring> fsMountOptions;
     bool allowUnsafe = false;
 
     ArgumentParser parser(std::wstring{commandLine}, WSL_BINARY_NAME, 0);
@@ -895,6 +914,7 @@ int Manage(_In_ std::wstring_view commandLine)
     parser.AddArgument(AbsolutePath(move), WSL_MANAGE_ARG_MOVE_OPTION_LONG, WSL_MANAGE_ARG_MOVE_OPTION);
     parser.AddArgument(defaultUser, WSL_MANAGE_ARG_SET_DEFAULT_USER_OPTION_LONG);
     parser.AddArgument(SizeString(resize), WSL_MANAGE_ARG_RESIZE_OPTION_LONG, WSL_MANAGE_ARG_RESIZE_OPTION);
+    parser.AddArgument(fsMountOptions, WSL_MANAGE_ARG_SET_FS_MOUNT_OPTIONS_LONG);
     parser.AddArgument(allowUnsafe, WSL_MANAGE_ARG_ALLOW_UNSAFE);
     parser.Parse();
 
@@ -903,7 +923,7 @@ int Manage(_In_ std::wstring_view commandLine)
     wsl::windows::common::SvcComm service;
     auto distroGuid = service.GetDistributionId(distribution);
 
-    if (sparse.has_value() + move.has_value() + defaultUser.has_value() + resize.has_value() != 1)
+    if (sparse.has_value() + move.has_value() + defaultUser.has_value() + resize.has_value() + fsMountOptions.has_value() != 1)
     {
         THROW_HR(WSL_E_INVALID_USAGE);
     }
@@ -950,6 +970,10 @@ int Manage(_In_ std::wstring_view commandLine)
     {
         THROW_IF_FAILED(service.ResizeDistribution(&distroGuid, resize.value()));
     }
+    else if (fsMountOptions)
+    {
+        service.SetFsMountOptions(&distroGuid, fsMountOptions->c_str());
+    }
 
     wsl::windows::common::wslutil::PrintSystemError(ERROR_SUCCESS);
     return 0;