virtiofs: add support for mounting directories (not just full volumes)

src/linux/init/config.cpp

@@ -1729,10 +1729,6 @@ Return Value:
         if (strcmp(MountEnum.Current().FileSystemType, PLAN9_FS_TYPE) == 0)
         {
             MountSource = UtilParsePlan9MountSource(MountEnum.Current().SuperOptions);
-            if (MountSource.empty())
-            {
-                continue;
-            }
         }
         else if (strcmp(MountEnum.Current().FileSystemType, DRVFS_FS_TYPE) == 0)
         {
@@ -1741,13 +1737,18 @@ Return Value:
         }
         else if (strcmp(MountEnum.Current().FileSystemType, VIRTIO_FS_TYPE) == 0)
         {
-            MountSource = UtilParseVirtiofsMountSource(MountEnum.Current().Source);
+            MountSource = QueryVirtiofsMountSource(MountEnum.Current().Source);
         }
         else
         {
             continue;
         }
 
+        if (MountSource.empty())
+        {
+            continue;
+        }
+
         auto letter = ConfigGetDriveLetter(MountSource);
         if (letter.has_value())
         {
@@ -2445,17 +2446,10 @@ try
                 NewMountOptions += ',';
             }
 
-            MountPlan9Filesystem(NewSource, MountEntry.MountPoint, NewMountOptions.c_str(), Message->Admin, Config);
+            MountPlan9Share(NewSource, MountEntry.MountPoint, NewMountOptions.c_str(), Message->Admin, Config);
         }
         else if (strcmp(MountEntry.FileSystemType, VIRTIO_FS_TYPE) == 0)
         {
-            std::string_view Source = MountEntry.Source;
-            std::string_view OldTag = Message->Admin ? LX_INIT_DRVFS_VIRTIO_TAG : LX_INIT_DRVFS_ADMIN_VIRTIO_TAG;
-            if (!wsl::shared::string::StartsWith(Source, OldTag))
-            {
-                continue;
-            }
-
             RemountVirtioFs(MountEntry.Source, MountEntry.MountPoint, MountEntry.MountOptions, Message->Admin);
         }
         else

src/linux/init/drvfs.cpp

@@ -298,70 +298,12 @@ try
     {
         return MountFilesystem(DRVFS_FS_TYPE, Source, Target, Options, ExitCode);
     }
-
-    // Use virtiofs if the source of the mount is the root of a drive; otherwise, use 9p.
-    if (WSL_USE_VIRTIO_FS(Config))
-    {
-        if (wsl::shared::string::IsDriveRoot(Source))
-        {
-            return MountVirtioFs(Source, Target, Options, Admin, Config, ExitCode);
-        }
-
-        LOG_WARNING("virtiofs is only supported for mounting full drives, using 9p to mount {}", Source);
-    }
-
-    //
-    // Check if the path is a UNC path.
-    //
-
-    const char* Plan9Source;
-    std::string UncSource;
-    if ((strlen(Source) >= PLAN9_UNC_PREFIX_LENGTH) && ((Source[0] == '/') || (Source[0] == '\\')) &&
-        ((Source[1] == '/') || (Source[1] == '\\')))
+    else if (WSL_USE_VIRTIO_FS(Config))
     {
-        UncSource = PLAN9_UNC_TRANSLATED_PREFIX;
-        UncSource += &Source[PLAN9_UNC_PREFIX_LENGTH];
-        Plan9Source = UncSource.c_str();
-    }
-    else
-    {
-        Plan9Source = Source;
+        return MountVirtioFs(Source, Target, Options, Admin, Config, ExitCode);
     }
 
-    //
-    // Check whether to use the elevated or regular 9p server.
-    //
-
-    bool Elevated = Admin.has_value() ? Admin.value() : IsDrvfsElevated();
-
-    //
-    // Initialize mount options.
-    //
-
-    auto Plan9Options = std::format("{};path={}", PLAN9_ANAME_DRVFS, Plan9Source);
-
-    //
-    // N.B. The cache option is added to the start of this so if the user
-    //      specifies one explicitly, it will override the default.
-    //
-
-    std::string MountOptions = "cache=mmap,";
-    auto ParsedOptions = ConvertDrvfsMountOptionsToPlan9(Options ? Options : "", Config);
-    Plan9Options += ParsedOptions.first;
-    MountOptions += ParsedOptions.second;
-
-    //
-    // Append the 9p mount options to the end of the other mount options and perform the mount operation.
-    //
-
-    MountOptions += Plan9Options;
-
-    if (MountPlan9Filesystem(Source, Target, MountOptions.c_str(), Elevated, Config, ExitCode) < 0)
-    {
-        return -1;
-    }
-
-    return 0;
+    return MountPlan9(Source, Target, Options, Admin, Config, ExitCode);
 }
 CATCH_RETURN_ERRNO()
 
@@ -407,7 +349,7 @@ Return Value:
     return ExitCode;
 }
 
-int MountPlan9Filesystem(const char* Source, const char* Target, const char* Options, bool Admin, const wsl::linux::WslDistributionConfig& Config, int* ExitCode)
+int MountPlan9Share(const char* Source, const char* Target, const char* Options, bool Admin, const wsl::linux::WslDistributionConfig& Config, int* ExitCode)
 
 /*++
 
@@ -425,6 +367,8 @@ Routine Description:
 
     Admin - Supplies a boolean specifying if the admin share should be used.
 
+    Config - Supplies the distribution configuration.
+
     ExitCode - Supplies an optional pointer that receives the exit code.
 
 Return Value:
@@ -452,10 +396,95 @@ Return Value:
 
         MountOptions =
             std::format("msize={},trans=fd,rfdno={},wfdno={},{}", LX_INIT_UTILITY_VM_PLAN9_BUFFER_SIZE, Fd.get(), Fd.get(), Options);
+
         return MountFilesystem(PLAN9_FS_TYPE, Source, Target, MountOptions.c_str(), ExitCode);
     }
 }
 
+int MountPlan9(const char* Source, const char* Target, const char* Options, std::optional<bool> Admin, const wsl::linux::WslDistributionConfig& Config, int* ExitCode)
+
+/*++
+
+Routine Description:
+
+    This routine will perform a DrvFs mount using Plan9.
+
+Arguments:
+
+    Source - Supplies the mount source.
+
+    Target - Supplies the mount target.
+
+    Options - Supplies the mount options.
+
+    Admin - Supplies an optional boolean to specify if the admin or non-admin share should be used.
+
+    Config - Supplies the distribution configuration.
+
+    ExitCode - Supplies an optional pointer that receives the exit code.
+
+Return Value:
+
+    0 on success, -1 on failure.
+
+--*/
+
+try
+{
+    //
+    // Check if the path is a UNC path.
+    //
+
+    const char* Plan9Source;
+    std::string UncSource;
+    if ((strlen(Source) >= PLAN9_UNC_PREFIX_LENGTH) && ((Source[0] == '/') || (Source[0] == '\\')) &&
+        ((Source[1] == '/') || (Source[1] == '\\')))
+    {
+        UncSource = PLAN9_UNC_TRANSLATED_PREFIX;
+        UncSource += &Source[PLAN9_UNC_PREFIX_LENGTH];
+        Plan9Source = UncSource.c_str();
+    }
+    else
+    {
+        Plan9Source = Source;
+    }
+
+    //
+    // Check whether to use the elevated or regular 9p server.
+    //
+
+    bool Elevated = Admin.has_value() ? Admin.value() : IsDrvfsElevated();
+
+    //
+    // Initialize mount options.
+    //
+
+    auto Plan9Options = std::format("{};path={}", PLAN9_ANAME_DRVFS, Plan9Source);
+
+    //
+    // N.B. The cache option is added to the start of this so if the user
+    //      specifies one explicitly, it will override the default.
+    //
+
+    std::string MountOptions = "cache=mmap,";
+    auto ParsedOptions = ConvertDrvfsMountOptionsToPlan9(Options ? Options : "", Config);
+    Plan9Options += ParsedOptions.first;
+    MountOptions += ParsedOptions.second;
+
+    //
+    // Append the 9p mount options to the end of the other mount options and perform the mount operation.
+    //
+
+    MountOptions += Plan9Options;
+    if (MountPlan9Share(Source, Target, MountOptions.c_str(), Elevated, Config, ExitCode) < 0)
+    {
+        return -1;
+    }
+
+    return 0;
+}
+CATCH_RETURN_ERRNO()
+
 int MountVirtioFs(const char* Source, const char* Target, const char* Options, std::optional<bool> Admin, const wsl::linux::WslDistributionConfig& Config, int* ExitCode)
 
 /*++
@@ -486,8 +515,6 @@ Return Value:
 
 try
 {
-    assert(wsl::shared::string::IsDriveRoot(Source));
-
     //
     // Check whether to use the elevated or non-elevated virtiofs server.
     //
@@ -516,7 +543,7 @@ try
     AddShare.WriteString(AddShare->OptionsOffset, Plan9Options);
 
     //
-    // Connect to the wsl service to add the virtiofs share.
+    // Connect to the wsl service to add the virtiofs share. If adding the share fails, fallback to mounting using Plan9.
     //
 
     wsl::shared::SocketChannel Channel{UtilConnectVsock(LX_INIT_UTILITY_VM_VIRTIOFS_PORT, true), "VirtoFs"};
@@ -527,11 +554,10 @@ try
 
     gsl::span<gsl::byte> ResponseSpan;
     const auto& Response = Channel.Transaction<LX_INIT_ADD_VIRTIOFS_SHARE_MESSAGE>(AddShare.Span(), &ResponseSpan);
-
     if (Response.Result != 0)
     {
-        LOG_ERROR("Add virtiofs share for {} failed {}", Source, Response.Result);
-        return -1;
+        LOG_WARNING("Add virtiofs share for {} failed {}, falling back to Plan9", Source, Response.Result);
+        return MountPlan9(Source, Target, Options, Admin, Config, ExitCode);
     }
 
     //
@@ -596,3 +622,52 @@ try
     return MountWithRetry(Tag, Target, VIRTIO_FS_TYPE, Options);
 }
 CATCH_RETURN_ERRNO()
+
+std::string QueryVirtiofsMountSource(const char* Tag)
+
+/*++
+
+Routine Description:
+
+    This routine takes a virtiofs tag and determines the Windows path it refers to.
+
+Arguments:
+
+    Tag - Supplies the virtiofs tag to query.
+
+Return Value:
+
+    The mount source, an empty string on failure.
+
+--*/
+
+try
+{
+    wsl::shared::MessageWriter<LX_INIT_QUERY_VIRTIOFS_SHARE_MESSAGE> QueryShare(LxInitMessageQueryVirtioFsDevice);
+    QueryShare.WriteString(QueryShare->TagOffset, Tag);
+
+    //
+    // Connect to the host and send the query request.
+    //
+
+    wsl::shared::SocketChannel Channel{UtilConnectVsock(LX_INIT_UTILITY_VM_VIRTIOFS_PORT, true), "QueryVirtioFs"};
+    if (Channel.Socket() < 0)
+    {
+        return {};
+    }
+
+    gsl::span<gsl::byte> ResponseSpan;
+    const auto& Response = Channel.Transaction<LX_INIT_QUERY_VIRTIOFS_SHARE_MESSAGE>(QueryShare.Span(), &ResponseSpan);
+    if (Response.Result != 0)
+    {
+        LOG_ERROR("Query virtiofs share for {} failed {}", Tag, Response.Result);
+        return {};
+    }
+
+    return wsl::shared::string::FromSpan(ResponseSpan, Response.TagOffset);
+}
+catch (...)
+{
+    LOG_CAUGHT_EXCEPTION();
+    return {};
+}

src/linux/init/drvfs.h

@@ -23,9 +23,12 @@ int MountDrvfs(const char* Source, const char* Target, const char* Options, std:
 
 int MountDrvfsEntry(int Argc, char* Argv[]);
 
-int MountPlan9Filesystem(
-    const char* Source, const char* Target, const char* Options, bool Admin, const wsl::linux::WslDistributionConfig& Config, int* ExitCode = nullptr);
+int MountPlan9Share(const char* Source, const char* Target, const char* Options, bool Admin, const wsl::linux::WslDistributionConfig& Config, int* ExitCode = nullptr);
+
+int MountPlan9(const char* Source, const char* Target, const char* Options, std::optional<bool> Admin, const wsl::linux::WslDistributionConfig& Config, int* ExitCode);
 
 int MountVirtioFs(const char* Source, const char* Target, const char* Options, std::optional<bool> Admin, const wsl::linux::WslDistributionConfig& Config, int* ExitCode = nullptr);
 
 int RemountVirtioFs(const char* Tag, const char* Target, const char* Options, bool Admin);
+
+std::string QueryVirtiofsMountSource(const char* Tag);

src/linux/init/util.cpp

@@ -902,11 +902,12 @@ try
         }
         else if (strcmp(MountEnum.Current().FileSystemType, VIRTIO_FS_TYPE) == 0)
         {
-            MountSource = UtilParseVirtiofsMountSource(MountEnum.Current().Source);
+            MountSource = QueryVirtiofsMountSource(MountEnum.Current().Source);
             if (MountSource.empty())
             {
                 continue;
             }
+
             MountEnum.Current().Source = MountSource.data();
         }
         else if (strcmp(MountEnum.Current().FileSystemType, DRVFS_FS_TYPE) == 0)
@@ -2026,41 +2027,6 @@ Return Value:
     return {};
 }
 
-std::string UtilParseVirtiofsMountSource(std::string_view Source)
-
-/*++
-
-Routine Description:
-
-    This routine parses the mount source to determine the actual source of a
-    a VirtioFs mount.
-
-Arguments:
-
-    Source - Supplies the source string.
-
-Return Value:
-
-    The mount source, or NULL if the source is not valid.
-
---*/
-
-{
-    std::string MountSource{};
-    if (wsl::shared::string::StartsWith(Source, LX_INIT_DRVFS_ADMIN_VIRTIO_TAG) && (Source.size() >= sizeof(LX_INIT_DRVFS_ADMIN_VIRTIO_TAG)))
-    {
-        MountSource = Source[sizeof(LX_INIT_DRVFS_ADMIN_VIRTIO_TAG) - 1];
-        MountSource += ":";
-    }
-    else if (wsl::shared::string::StartsWith(Source, LX_INIT_DRVFS_VIRTIO_TAG) && (Source.size() >= sizeof(LX_INIT_DRVFS_VIRTIO_TAG)))
-    {
-        MountSource = Source[sizeof(LX_INIT_DRVFS_VIRTIO_TAG) - 1];
-        MountSource += ":";
-    }
-
-    return MountSource;
-}
-
 std::vector<char> UtilParseWslEnv(char* NtEnvironment)
 
 /*++