2019-07-11 22:04:23 +00:00
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// 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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"errors"
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"fmt"
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"io"
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"os"
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"sync"
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2019-07-17 21:46:57 +00:00
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"gvisor.dev/gvisor/pkg/abi/linux"
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"gvisor.dev/gvisor/pkg/sentry/context"
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"gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout"
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"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
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"gvisor.dev/gvisor/pkg/sentry/vfs"
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"gvisor.dev/gvisor/pkg/syserror"
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)
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// filesystemType implements vfs.FilesystemType.
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type filesystemType struct{}
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// Compiles only if filesystemType implements vfs.FilesystemType.
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var _ vfs.FilesystemType = (*filesystemType)(nil)
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2019-07-23 22:50:35 +00:00
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// filesystem implements vfs.FilesystemImpl.
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type filesystem struct {
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// TODO(b/134676337): Remove when all methods have been implemented.
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vfs.FilesystemImpl
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vfsfs vfs.Filesystem
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// mu serializes changes to the dentry tree and the usage of the read seeker.
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mu sync.Mutex
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// dev is the ReadSeeker for the underlying fs device. It is protected by mu.
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//
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// The ext filesystems aim to maximize locality, i.e. place all the data
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// blocks of a file close together. On a spinning disk, locality reduces the
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// amount of movement of the head hence speeding up IO operations. On an SSD
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// there are no moving parts but locality increases the size of each transer
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// request. Hence, having mutual exclusion on the read seeker while reading a
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// file *should* 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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dev io.ReadSeeker
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// inodeCache maps absolute inode numbers to the corresponding Inode struct.
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// Inodes should be removed from this once their reference count hits 0.
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//
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// Protected by mu because every addition and removal from this corresponds to
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// a change in the dentry tree.
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inodeCache map[uint32]*inode
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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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// Compiles only if filesystem implements vfs.FilesystemImpl.
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var _ vfs.FilesystemImpl = (*filesystem)(nil)
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// getDeviceFd returns the read seeker to the underlying device.
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// Currently there are two ways of mounting an ext(2/3/4) fs:
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// 1. Specify a mount with our internal special MountType in the OCI spec.
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// 2. Expose the device to the container and mount it from application layer.
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func getDeviceFd(source string, opts vfs.NewFilesystemOptions) (io.ReadSeeker, error) {
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if opts.InternalData == nil {
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// User mount call.
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// TODO(b/134676337): Open the device specified by `source` and return that.
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panic("unimplemented")
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}
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// NewFilesystem call originated from within the sentry.
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fd, ok := opts.InternalData.(uintptr)
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if !ok {
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return nil, errors.New("internal data for ext fs must be a uintptr containing the file descriptor to device")
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}
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// We do not close this file because that would close the underlying device
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// file descriptor (which is required for reading the fs from disk).
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// TODO(b/134676337): Use pkg/fd instead.
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deviceFile := os.NewFile(fd, source)
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if deviceFile == nil {
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return nil, fmt.Errorf("ext4 device file descriptor is not valid: %d", fd)
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}
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return deviceFile, nil
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}
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// NewFilesystem implements vfs.FilesystemType.NewFilesystem.
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func (fstype filesystemType) NewFilesystem(ctx context.Context, creds *auth.Credentials, source string, opts vfs.NewFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
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dev, err := getDeviceFd(source, opts)
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if err != nil {
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return nil, nil, err
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}
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fs := filesystem{dev: dev, inodeCache: make(map[uint32]*inode)}
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fs.vfsfs.Init(&fs)
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fs.sb, err = readSuperBlock(dev)
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if err != nil {
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return nil, 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, 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, nil, err
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}
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return &fs.vfsfs, nil, nil
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}
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// getOrCreateInode gets the inode corresponding to the inode number passed in.
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// It creates a new one with the given inode number if one does not exist.
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//
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// Preconditions: must be holding fs.mu.
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func (fs *filesystem) getOrCreateInode(inodeNum uint32) (*inode, error) {
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if in, ok := fs.inodeCache[inodeNum]; ok {
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return in, nil
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}
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in, err := newInode(fs.dev, fs.sb, fs.bgs, inodeNum)
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if err != nil {
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return nil, err
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}
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fs.inodeCache[inodeNum] = in
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return in, nil
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}
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