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64 lines
2.4 KiB
64 lines
2.4 KiB
// +build !linux,!netbsd,!freebsd,!darwin
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/*
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* Minio Cloud Storage, (C) 2019-2020 Minio, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package disk
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import (
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"os"
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)
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// OpenBSD, Windows, and illumos do not support O_DIRECT.
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// On Windows there is no documentation on disabling O_DIRECT.
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// For these systems we do not attempt to build the 'directio' dependency since
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// the O_DIRECT symbol may not be exposed resulting in a failed build.
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//
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//
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// On illumos an explicit O_DIRECT flag is not necessary for two primary
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// reasons. Note that ZFS is effectively the default filesystem on illumos
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// systems.
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//
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// One benefit of using DirectIO on Linux is that the page cache will not be
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// polluted with single-access data. The ZFS read cache (ARC) is scan-resistant
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// so there is no risk of polluting the entire cache with data accessed once.
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// Another goal of DirectIO is to minimize the mutation of data by the kernel
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// before issuing IO to underlying devices. ZFS users often enable features like
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// compression and checksumming which currently necessitates mutating data in
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// the kernel.
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//
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// DirectIO semantics for a filesystem like ZFS would be quite different than
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// the semantics on filesystems like XFS, and these semantics are not
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// implemented at this time.
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// For more information on why typical DirectIO semantics do not apply to ZFS
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// see this ZFS-on-Linux commit message:
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// https://github.com/openzfs/zfs/commit/a584ef26053065f486d46a7335bea222cb03eeea
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// OpenFileDirectIO wrapper around os.OpenFile nothing special
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func OpenFileDirectIO(filePath string, flag int, perm os.FileMode) (*os.File, error) {
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return os.OpenFile(filePath, flag, perm)
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}
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// DisableDirectIO is a no-op
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func DisableDirectIO(f *os.File) error {
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return nil
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}
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// AlignedBlock simply returns an unaligned buffer
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// for systems that do not support DirectIO.
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func AlignedBlock(BlockSize int) []byte {
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return make([]byte, BlockSize)
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}
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