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66 lines
2.5 KiB
Go
66 lines
2.5 KiB
Go
// +build !linux,!netbsd,!freebsd,!darwin
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// Copyright (c) 2015-2021 MinIO, Inc.
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//
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// This file is part of MinIO Object Storage stack
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Affero General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Affero General Public License for more details.
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//
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// You should have received a copy of the GNU Affero General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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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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