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[Support] Check whether a file is local by its handle on Windows #225

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[Support] Check whether a file is local by its handle on Windows #225

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75 changes: 59 additions & 16 deletions llvm/lib/Support/Windows/Path.inc
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,7 @@
#include <shellapi.h>
#include <shlobj.h>
#include <winioctl.h>
#include <winternl.h>

#undef max

Expand All @@ -43,6 +44,32 @@ typedef int errno_t;
#pragma comment(lib, "ole32.lib") // This provides CoTaskMemFree
#endif

#ifndef __MINGW32__
// The Windows SDK does not declare these types.
// The WDK declares the types in `wdm.h` and `NtQueryVolumeInformationFile`
// in `ntifs.h`.
// MinGW-w64 declares all three in `winternl.h`.
typedef enum _FSINFOCLASS { FileFsDeviceInformation = 4 } FS_INFORMATION_CLASS;

typedef struct _FILE_FS_DEVICE_INFORMATION {
DEVICE_TYPE DeviceType;
ULONG Characteristics;
} FILE_FS_DEVICE_INFORMATION;

// Exported by `ntdll.dll`.
extern "C" NTSYSAPI NTSTATUS NTAPI NtQueryVolumeInformationFile(
HANDLE FileHandle, PIO_STATUS_BLOCK IoStatusBlock, PVOID FsInformation,
ULONG Length, FS_INFORMATION_CLASS FsInformationClass);
#endif

// Defined only in `wdm.h` in WDK and MinGW-w64.
#ifndef FILE_REMOVABLE_MEDIA
#define FILE_REMOVABLE_MEDIA 0x00000001
#endif
#ifndef FILE_REMOTE_DEVICE
#define FILE_REMOTE_DEVICE 0x00000010
#endif

using namespace llvm;

using llvm::sys::windows::CurCPToUTF16;
Expand Down Expand Up @@ -549,18 +576,41 @@ static std::error_code realPathFromHandle(HANDLE H,
return std::error_code();
}

std::error_code is_local(int FD, bool &Result) {
sandbox::violationIfEnabled();
/// Returns true if the volume holding \p Handle is known to be a fixed local
/// disk. Returns false if it is not or if that could not be determined.
static bool isLocalByQueryVolumeInformationFile(HANDLE Handle) {
IO_STATUS_BLOCK IoStatus;
FILE_FS_DEVICE_INFORMATION Info;
if (::NtQueryVolumeInformationFile(Handle, &IoStatus, &Info, sizeof(Info),
FileFsDeviceInformation) < 0)
return false;

SmallVector<wchar_t, 128> FinalPath;
HANDLE Handle = reinterpret_cast<HANDLE>(_get_osfhandle(FD));
return (Info.DeviceType == FILE_DEVICE_DISK ||
Info.DeviceType == FILE_DEVICE_DISK_FILE_SYSTEM) &&
!(Info.Characteristics & (FILE_REMOVABLE_MEDIA | FILE_REMOTE_DEVICE));
}

static std::error_code is_local_internal(HANDLE Handle, bool &Result) {
// Fast path for the common case: an ordinary local disk, one system call on
// the handle. Everything else goes through the path-based check below.
if (isLocalByQueryVolumeInformationFile(Handle)) {
Result = true;
return std::error_code();
}

SmallVector<wchar_t, 128> FinalPath;
if (std::error_code EC = realPathFromHandle(Handle, FinalPath))
return EC;

return is_local_internal(FinalPath, Result);
}

std::error_code is_local(int FD, bool &Result) {
sandbox::violationIfEnabled();

HANDLE Handle = reinterpret_cast<HANDLE>(_get_osfhandle(FD));
return is_local_internal(Handle, Result);
}

static std::error_code setDeleteDisposition(HANDLE Handle, bool Delete) {
// Clear the FILE_DISPOSITION_INFO flag first, before checking if it's a
// network file. On Windows 7 the function realPathFromHandle() below fails
Expand All @@ -577,12 +627,8 @@ static std::error_code setDeleteDisposition(HANDLE Handle, bool Delete) {
// Check if the file is on a network (non-local) drive. If so, don't
// continue when DeleteFile is true, since it prevents opening the file for
// writes.
SmallVector<wchar_t, 128> FinalPath;
if (std::error_code EC = realPathFromHandle(Handle, FinalPath))
return EC;

bool IsLocal;
if (std::error_code EC = is_local_internal(FinalPath, IsLocal))
if (std::error_code EC = is_local_internal(Handle, IsLocal))
return EC;

if (!IsLocal)
Expand Down Expand Up @@ -1171,12 +1217,9 @@ void mapped_file_region::unmapImpl() {
// cases where we do the flushing. Only do the flushing if we aren't
// sure we are on a local file system.
bool IsLocal = false;
SmallVector<wchar_t, 128> FinalPath;
if (!realPathFromHandle(FileHandle, FinalPath)) {
// Not checking the return value here - if the check fails, assume the
// file isn't local.
is_local_internal(FinalPath, IsLocal);
}
// Not checking the return value here - if the check fails, assume the
// file isn't local.
is_local_internal(FileHandle, IsLocal);
DoFlush = !IsLocal;
}
if (DoFlush)
Expand Down