1 // Copyright 2015 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 package fileutil 16 17 import ( 18 "io" 19 "os" 20 ) 21 22 // Preallocate tries to allocate the space for given 23 // file. This operation is only supported on linux by a 24 // few filesystems (btrfs, ext4, etc.). 25 // If the operation is unsupported, no error will be returned. 26 // Otherwise, the error encountered will be returned. 27 func Preallocate(f *os.File, sizeInBytes int64, extendFile bool) error { 28 if sizeInBytes == 0 { 29 // fallocate will return EINVAL if length is 0; skip 30 return nil 31 } 32 if extendFile { 33 return preallocExtend(f, sizeInBytes) 34 } 35 return preallocFixed(f, sizeInBytes) 36 } 37 38 func preallocExtendTrunc(f *os.File, sizeInBytes int64) error { 39 curOff, err := f.Seek(0, io.SeekCurrent) 40 if err != nil { 41 return err 42 } 43 size, err := f.Seek(sizeInBytes, io.SeekEnd) 44 if err != nil { 45 return err 46 } 47 if _, err = f.Seek(curOff, io.SeekStart); err != nil { 48 return err 49 } 50 if sizeInBytes > size { 51 return nil 52 } 53 return f.Truncate(sizeInBytes) 54 } 55