github.com/petermattis/pebble@v0.0.0-20190905164901-ab51a2166067/vfs/preallocate_darwin.go (about)

     1  // Copyright 2016 The etcd Authors
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // +build darwin
    16  
    17  package vfs
    18  
    19  import (
    20  	"syscall"
    21  	"unsafe"
    22  )
    23  
    24  func preallocExtend(fd uintptr, offset, length int64) error {
    25  	if err := preallocFixed(fd, offset, length); err != nil {
    26  		return err
    27  	}
    28  	return syscall.Ftruncate(int(fd), offset+length)
    29  }
    30  
    31  func preallocFixed(fd uintptr, offset, length int64) error {
    32  	// allocate all requested space or no space at all
    33  	// TODO: allocate contiguous space on disk with F_ALLOCATECONTIG flag
    34  	fstore := &syscall.Fstore_t{
    35  		Flags:   syscall.F_ALLOCATEALL,
    36  		Posmode: syscall.F_PEOFPOSMODE,
    37  		Length:  length}
    38  	p := unsafe.Pointer(fstore)
    39  	_, _, errno := syscall.Syscall(syscall.SYS_FCNTL, fd, uintptr(syscall.F_PREALLOCATE), uintptr(p))
    40  	if errno == 0 || errno == syscall.ENOTSUP {
    41  		return nil
    42  	}
    43  
    44  	// wrong argument to fallocate syscall
    45  	if errno == syscall.EINVAL {
    46  		// filesystem "st_blocks" are allocated in the units of
    47  		// "Allocation Block Size" (run "diskutil info /" command)
    48  		var stat syscall.Stat_t
    49  		syscall.Fstat(int(fd), &stat)
    50  
    51  		// syscall.Statfs_t.Bsize is "optimal transfer block size"
    52  		// and contains matching 4096 value when latest OS X kernel
    53  		// supports 4,096 KB filesystem block size
    54  		var statfs syscall.Statfs_t
    55  		syscall.Fstatfs(int(fd), &statfs)
    56  		blockSize := int64(statfs.Bsize)
    57  
    58  		if stat.Blocks*blockSize >= offset+length {
    59  			// enough blocks are already allocated
    60  			return nil
    61  		}
    62  	}
    63  	return errno
    64  }