ext: filesystem boilerplate code.

PiperOrigin-RevId: 259865366

1 files changed, 137 insertions, 0 deletions

diff --git a/pkg/sentry/fs/ext/filesystem.go b/pkg/sentry/fs/ext/filesystem.go
new file mode 100644
index 000000000..7150e75a5
--- /dev/null
+++ b/pkg/sentry/fs/ext/filesystem.go
@@ -0,0 +1,137 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ext
+
+import (
+	"io"
+	"sync"
+
+	"gvisor.dev/gvisor/pkg/sentry/context"
+	"gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+// filesystem implements vfs.FilesystemImpl.
+type filesystem struct {
+	// TODO(b/134676337): Remove when all methods have been implemented.
+	vfs.FilesystemImpl
+
+	vfsfs vfs.Filesystem
+
+	// mu serializes changes to the Dentry tree and the usage of the read seeker.
+	mu sync.Mutex
+
+	// dev is the ReadSeeker for the underlying fs device. It is protected by mu.
+	//
+	// The ext filesystems aim to maximize locality, i.e. place all the data
+	// blocks of a file close together. On a spinning disk, locality reduces the
+	// amount of movement of the head hence speeding up IO operations. On an SSD
+	// there are no moving parts but locality increases the size of each transer
+	// request. Hence, having mutual exclusion on the read seeker while reading a
+	// file *should* help in achieving the intended performance gains.
+	//
+	// Note: This synchronization was not coupled with the ReadSeeker itself
+	// because we want to synchronize across read/seek operations for the
+	// performance gains mentioned above. Helps enforcing one-file-at-a-time IO.
+	dev io.ReadSeeker
+
+	// inodeCache maps absolute inode numbers to the corresponding Inode struct.
+	// Inodes should be removed from this once their reference count hits 0.
+	//
+	// Protected by mu because every addition and removal from this corresponds to
+	// a change in the dentry tree.
+	inodeCache map[uint32]*inode
+
+	// sb represents the filesystem superblock. Immutable after initialization.
+	sb disklayout.SuperBlock
+
+	// bgs represents all the block group descriptors for the filesystem.
+	// Immutable after initialization.
+	bgs []disklayout.BlockGroup
+}
+
+// Compiles only if filesystem implements vfs.FilesystemImpl.
+var _ vfs.FilesystemImpl = (*filesystem)(nil)
+
+// getOrCreateInode gets the inode corresponding to the inode number passed in.
+// It creates a new one with the given inode number if one does not exist.
+//
+// Preconditions: must be holding fs.mu.
+func (fs *filesystem) getOrCreateInode(inodeNum uint32) (*inode, error) {
+	if in, ok := fs.inodeCache[inodeNum]; ok {
+		return in, nil
+	}
+
+	in, err := newInode(fs.dev, fs.sb, fs.bgs, inodeNum)
+	if err != nil {
+		return nil, err
+	}
+
+	fs.inodeCache[inodeNum] = in
+	return in, nil
+}
+
+// Release implements vfs.FilesystemImpl.Release.
+func (fs *filesystem) Release() {
+}
+
+// Sync implements vfs.FilesystemImpl.Sync.
+func (fs *filesystem) Sync(ctx context.Context) error {
+	// This is a readonly filesystem for now.
+	return nil
+}
+
+// The vfs.FilesystemImpl functions below return EROFS because their respective
+// man pages say that EROFS must be returned if the path resolves to a file on
+// a read-only filesystem.
+
+// TODO(b/134676337): Implement path traversal and return EROFS only if the
+// path resolves to a Dentry within ext fs.
+
+// MkdirAt implements vfs.FilesystemImpl.MkdirAt.
+func (fs *filesystem) MkdirAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.MkdirOptions) error {
+	return syserror.EROFS
+}
+
+// MknodAt implements vfs.FilesystemImpl.MknodAt.
+func (fs *filesystem) MknodAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.MknodOptions) error {
+	return syserror.EROFS
+}
+
+// RenameAt implements vfs.FilesystemImpl.RenameAt.
+func (fs *filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, vd vfs.VirtualDentry, opts vfs.RenameOptions) error {
+	return syserror.EROFS
+}
+
+// RmdirAt implements vfs.FilesystemImpl.RmdirAt.
+func (fs *filesystem) RmdirAt(ctx context.Context, rp *vfs.ResolvingPath) error {
+	return syserror.EROFS
+}
+
+// SetStatAt implements vfs.FilesystemImpl.SetStatAt.
+func (fs *filesystem) SetStatAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.SetStatOptions) error {
+	return syserror.EROFS
+}
+
+// SymlinkAt implements vfs.FilesystemImpl.SymlinkAt.
+func (fs *filesystem) SymlinkAt(ctx context.Context, rp *vfs.ResolvingPath, target string) error {
+	return syserror.EROFS
+}
+
+// UnlinkAt implements vfs.FilesystemImpl.UnlinkAt.
+func (fs *filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error {
+	return syserror.EROFS
+}