syscall: implement Ftruncate using a single syscall on Windows

Ftruncate can be implemented on Windows using a single syscall. This
makes the implementation more efficient and less prone to races when
used in combination with other Seek calls.

Change-Id: I5d9f780fba2710403fce89d3325e519f33ad9ae8
Reviewed-on: https://go-review.googlesource.com/c/go/+/618835
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/src/syscall/syscall_windows.go b/src/syscall/syscall_windows.go
index d49ee522c4fe883fd1f27ec05348d6d154b30a96..359681e920756fec14a1fe73072165e80e655b98 100644 (file)
--- a/src/syscall/syscall_windows.go
+++ b/src/syscall/syscall_windows.go
@@ -323,6 +323,7 @@ func NewCallbackCDecl(fn any) uintptr {
 //sys  Process32First(snapshot Handle, procEntry *ProcessEntry32) (err error) = kernel32.Process32FirstW
 //sys  Process32Next(snapshot Handle, procEntry *ProcessEntry32) (err error) = kernel32.Process32NextW
 //sys  DeviceIoControl(handle Handle, ioControlCode uint32, inBuffer *byte, inBufferSize uint32, outBuffer *byte, outBufferSize uint32, bytesReturned *uint32, overlapped *Overlapped) (err error)
+//sys  setFileInformationByHandle(handle Handle, fileInformationClass uint32, buf unsafe.Pointer, bufsize uint32) (err error) = kernel32.SetFileInformationByHandle
 // This function returns 1 byte BOOLEAN rather than the 4 byte BOOL.
 //sys  CreateSymbolicLink(symlinkfilename *uint16, targetfilename *uint16, flags uint32) (err error) [failretval&0xff==0] = CreateSymbolicLinkW
 //sys  CreateHardLink(filename *uint16, existingfilename *uint16, reserved uintptr) (err error) [failretval&0xff==0] = CreateHardLinkW
@@ -610,20 +611,13 @@ func ComputerName() (name string, err error) {
 }
 
 func Ftruncate(fd Handle, length int64) (err error) {
-       curoffset, e := Seek(fd, 0, 1)
-       if e != nil {
-               return e
-       }
-       defer Seek(fd, curoffset, 0)
-       _, e = Seek(fd, length, 0)
-       if e != nil {
-               return e
+       type _FILE_END_OF_FILE_INFO struct {
+               EndOfFile int64
        }
-       e = SetEndOfFile(fd)
-       if e != nil {
-               return e
-       }
-       return nil
+       const FileEndOfFileInfo = 6
+       var info _FILE_END_OF_FILE_INFO
+       info.EndOfFile = length
+       return setFileInformationByHandle(fd, FileEndOfFileInfo, unsafe.Pointer(&info), uint32(unsafe.Sizeof(info)))
 }
 
 func Gettimeofday(tv *Timeval) (err error) {

diff --git a/src/syscall/zsyscall_windows.go b/src/syscall/zsyscall_windows.go
index d8d8594a55611129f05179e898d30980409f6ec2..c0585a6df2eb118e83b21fda2f613e3c2a09cfd1 100644 (file)
--- a/src/syscall/zsyscall_windows.go
+++ b/src/syscall/zsyscall_windows.go
@@ -150,6 +150,7 @@ var (
        procSetEnvironmentVariableW            = modkernel32.NewProc("SetEnvironmentVariableW")
        procSetFileAttributesW                 = modkernel32.NewProc("SetFileAttributesW")
        procSetFileCompletionNotificationModes = modkernel32.NewProc("SetFileCompletionNotificationModes")
+       procSetFileInformationByHandle         = modkernel32.NewProc("SetFileInformationByHandle")
        procSetFilePointer                     = modkernel32.NewProc("SetFilePointer")
        procSetFileTime                        = modkernel32.NewProc("SetFileTime")
        procSetHandleInformation               = modkernel32.NewProc("SetHandleInformation")
@@ -1071,6 +1072,14 @@ func SetFileCompletionNotificationModes(handle Handle, flags uint8) (err error)
        return
 }
 
+func setFileInformationByHandle(handle Handle, fileInformationClass uint32, buf unsafe.Pointer, bufsize uint32) (err error) {
+       r1, _, e1 := Syscall6(procSetFileInformationByHandle.Addr(), 4, uintptr(handle), uintptr(fileInformationClass), uintptr(buf), uintptr(bufsize), 0, 0)
+       if r1 == 0 {
+               err = errnoErr(e1)
+       }
+       return
+}
+
 func SetFilePointer(handle Handle, lowoffset int32, highoffsetptr *int32, whence uint32) (newlowoffset uint32, err error) {
        r0, _, e1 := Syscall6(procSetFilePointer.Addr(), 4, uintptr(handle), uintptr(lowoffset), uintptr(unsafe.Pointer(highoffsetptr)), uintptr(whence), 0, 0)
        newlowoffset = uint32(r0)