From 2ffb8a1c97f6e6d39d3e34c86366e4859ac51656 Mon Sep 17 00:00:00 2001
From: Bill Zissimopoulos <billziss@navimatics.com>
Date: Sun, 24 May 2020 21:04:28 -0700
Subject: [PATCH] sys: FSP_FSCTL_QUERY_WINFSP

The FSP_FSCTL_QUERY_WINFSP code provides a simple method to determine if
the file system backing a file is a WinFsp file system. To use issue a

    DeviceIoControl(Handle, FSP_FSCTL_QUERY_WINFSP, 0, 0, 0, 0, &Bytes, 0)

If the return value is TRUE this is a WinFsp file system.
---
 inc/winfsp/fsctl.h           |  4 ++++
 src/sys/fsctl.c              |  4 ++++
 tst/winfsp-tests/info-test.c | 42 ++++++++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+)

diff --git a/inc/winfsp/fsctl.h b/inc/winfsp/fsctl.h
index 353bf5fb..4615fa85 100644
--- a/inc/winfsp/fsctl.h
+++ b/inc/winfsp/fsctl.h
@@ -71,6 +71,10 @@ extern const __declspec(selectany) GUID FspFsvrtDeviceClassGuid =
 #define FSP_FSCTL_TRANSACT_INTERNAL     \
     CTL_CODE(FILE_DEVICE_FILE_SYSTEM, 0x800 + 'I', METHOD_NEITHER, FILE_ANY_ACCESS)
 
+/* fsvol device codes */
+#define FSP_FSCTL_QUERY_WINFSP          \
+    CTL_CODE(FILE_DEVICE_FILE_SYSTEM, 0x800 + '?', METHOD_BUFFERED, FILE_ANY_ACCESS)
+
 #define FSP_FSCTL_VOLUME_PARAMS_PREFIX  "\\VolumeParams="
 
 #define FSP_FSCTL_VOLUME_NAME_SIZE      (64 * sizeof(WCHAR))
diff --git a/src/sys/fsctl.c b/src/sys/fsctl.c
index 1b9bc5de..175a6096 100644
--- a/src/sys/fsctl.c
+++ b/src/sys/fsctl.c
@@ -698,6 +698,10 @@ static NTSTATUS FspFsvolFileSystemControl(
         case FSP_FSCTL_WORK_BEST_EFFORT:
             Result = FspVolumeWork(FsvolDeviceObject, Irp, IrpSp);
             break;
+        case FSP_FSCTL_QUERY_WINFSP:
+            Irp->IoStatus.Information = 0;
+            Result = STATUS_SUCCESS;
+            break;
         case FSCTL_GET_REPARSE_POINT:
             Result = FspFsvolFileSystemControlReparsePoint(FsvolDeviceObject, Irp, IrpSp, FALSE);
             break;
diff --git a/tst/winfsp-tests/info-test.c b/tst/winfsp-tests/info-test.c
index b72f9c84..0d6b893e 100644
--- a/tst/winfsp-tests/info-test.c
+++ b/tst/winfsp-tests/info-test.c
@@ -1930,6 +1930,47 @@ void setvolinfo_test(void)
     }
 }
 
+void query_winfsp_dotest(ULONG Flags, PWSTR Prefix, ULONG FileInfoTimeout, BOOLEAN ExpectWinFsp)
+{
+    void* memfs = memfs_start_ex(Flags, FileInfoTimeout);
+
+    WCHAR FilePath[MAX_PATH];
+    HANDLE Handle;
+    DWORD BytesTransferred;
+
+    StringCbPrintfW(FilePath, sizeof FilePath, L"%s%s\\",
+        Prefix ? L"" : L"\\\\?\\GLOBALROOT", Prefix ? Prefix : memfs_volumename(memfs));
+
+    Handle = CreateFileW(FilePath,
+        0, FILE_SHARE_READ | FILE_SHARE_WRITE, 0, OPEN_EXISTING,
+        FILE_FLAG_BACKUP_SEMANTICS, 0);
+    ASSERT(INVALID_HANDLE_VALUE != Handle);
+
+    if (ExpectWinFsp)
+        ASSERT(DeviceIoControl(Handle, FSP_FSCTL_QUERY_WINFSP, 0, 0, 0, 0, &BytesTransferred, 0));
+    else
+        ASSERT(!DeviceIoControl(Handle, FSP_FSCTL_QUERY_WINFSP, 0, 0, 0, 0, &BytesTransferred, 0) &&
+            ERROR_INVALID_FUNCTION == GetLastError());
+
+    CloseHandle(Handle);
+
+    memfs_stop(memfs);
+}
+
+void query_winfsp_test(void)
+{
+    if (NtfsTests)
+    {
+        WCHAR DirBuf[MAX_PATH], DriveBuf[3];
+        GetTestDirectoryAndDrive(DirBuf, DriveBuf);
+        query_winfsp_dotest(-1, DriveBuf, 0, FALSE);
+    }
+    if (WinFspDiskTests)
+        query_winfsp_dotest(MemfsDisk, 0, 0, TRUE);
+    if (WinFspNetTests)
+        query_winfsp_dotest(MemfsNet, L"\\\\memfs\\share", 0, TRUE);
+}
+
 void info_tests(void)
 {
     if (!OptShareName)
@@ -1955,4 +1996,5 @@ void info_tests(void)
         TEST(rename_pid_test);
     TEST(getvolinfo_test);
     TEST(setvolinfo_test);
+    TEST(query_winfsp_test);
 }