76 lines
2.4 KiB
Go
76 lines
2.4 KiB
Go
// Copyright 2019 The gVisor Authors.
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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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// Package ext implements readonly ext(2/3/4) filesystems.
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package ext
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import (
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"io"
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"sync"
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"gvisor.dev/gvisor/pkg/abi/linux"
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"gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout"
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"gvisor.dev/gvisor/pkg/syserror"
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)
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// Filesystem implements vfs.FilesystemImpl.
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type Filesystem struct {
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// dev is the ReadSeeker for the underlying fs device and is protected by mu.
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dev io.ReadSeeker
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// mu synchronizes the usage of dev. The ext filesystems take locality into
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// condsideration, i.e. data blocks of a file will tend to be placed close
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// together. On a spinning disk, locality reduces the amount of movement of
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// the head hence speeding up IO operations. On an SSD there are no moving
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// parts but locality increases the size of each transer request. Hence,
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// having mutual exclusion on the read seeker while reading a file *should*
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// help in achieving the intended performance gains.
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//
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// Note: This synchronization was not coupled with the ReadSeeker itself
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// because we want to synchronize across read/seek operations for the
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// performance gains mentioned above. Helps enforcing one-file-at-a-time IO.
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mu sync.Mutex
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// sb represents the filesystem superblock. Immutable after initialization.
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sb disklayout.SuperBlock
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// bgs represents all the block group descriptors for the filesystem.
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// Immutable after initialization.
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bgs []disklayout.BlockGroup
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}
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// newFilesystem is the Filesystem constructor.
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func newFilesystem(dev io.ReadSeeker) (*Filesystem, error) {
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fs := Filesystem{dev: dev}
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var err error
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fs.sb, err = readSuperBlock(dev)
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if err != nil {
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return nil, err
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}
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if fs.sb.Magic() != linux.EXT_SUPER_MAGIC {
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// mount(2) specifies that EINVAL should be returned if the superblock is
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// invalid.
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return nil, syserror.EINVAL
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}
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fs.bgs, err = readBlockGroups(dev, fs.sb)
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if err != nil {
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return nil, err
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}
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return &fs, nil
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}
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