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ef1c2a2280
Adds support for sparse file hole punching in linux, windows, and darwin. Also adds a generic PunchAt method that just writes zeros instead of using the file Punch syscall. Updates tailscale/corp#21363 Signed-off-by: James Scott <jim@tailscale.com>
53 lines
1.7 KiB
Go
53 lines
1.7 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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//go:build windows
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package sparse
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import (
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"io/fs"
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"os"
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"syscall"
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"unsafe"
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"golang.org/x/sys/windows"
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)
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// punchAt for Windows also marks the file as sparse before it punches a hole in it.
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func punchAt(fd *os.File, off, size int64) error {
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// Windows is unique in that if you call FSCTL_SET_ZERO_DATA on a non sparse file it will just zero out the hole.
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// Ensure the file is marked as sparse before punching a hole.
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// Docs: https://learn.microsoft.com/en-us/windows/win32/api/winioctl/ni-winioctl-fsctl_set_zero_data#remarks
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err := markAsSparseFile(fd)
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if err != nil {
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return &fs.PathError{Op: "punchAt", Path: fd.Name(), Err: err}
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}
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fileHandle := syscall.Handle(fd.Fd())
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// https://learn.microsoft.com/en-us/windows/win32/api/winioctl/ns-winioctl-file_zero_data_information
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zeroData := struct {
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FileOffset uint64
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ByeondFinalZero uint64
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}{
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FileOffset: uint64(off),
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ByeondFinalZero: uint64(off + size),
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}
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var bytesReturned uint32
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err = syscall.DeviceIoControl(fileHandle, windows.FSCTL_SET_ZERO_DATA, (*byte)(unsafe.Pointer(&zeroData)), uint32(unsafe.Sizeof(zeroData)), nil, 0, &bytesReturned, nil)
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if err != nil {
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return &fs.PathError{Op: "punchAt", Path: fd.Name(), Err: err}
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}
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return err
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}
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func markAsSparseFile(file *os.File) error {
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fileHandle := syscall.Handle(file.Fd())
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var bytesReturned uint32
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// FSCTL_SET_SPARSE is the windows syscall to mark a file as sparse.
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// Docs: https://learn.microsoft.com/en-us/windows/win32/api/winioctl/ni-winioctl-fsctl_set_sparse
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return syscall.DeviceIoControl(fileHandle, windows.FSCTL_SET_SPARSE, nil, 0, nil, 0, &bytesReturned, nil)
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}
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