From: qmuntal <quimmuntal@gmail.com>
Date: Wed, 9 Oct 2024 08:12:57 +0000 (+0200)
Subject: syscall: implement Ftruncate using a single syscall on Windows
X-Git-Tag: go1.24rc1~719
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=0fd2d4d6c2101fb615a7546f49e92a2187191fb0;p=gostls13.git

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 d49ee522c4..359681e920 100644
--- 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 d8d8594a55..c0585a6df2 100644
--- 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)