ext: filesystem boilerplate code.

PiperOrigin-RevId: 259865366

3 files changed, 138 insertions, 61 deletions

diff --git a/pkg/sentry/fs/ext/BUILD b/pkg/sentry/fs/ext/BUILD
index e660e545d..2c15875f5 100644
--- a/pkg/sentry/fs/ext/BUILD
+++ b/pkg/sentry/fs/ext/BUILD
@@ -7,6 +7,7 @@ go_library(
     srcs = [
         "dentry.go",
         "ext.go",
+        "filesystem.go",
         "inode.go",
         "utils.go",
     ],
diff --git a/pkg/sentry/fs/ext/ext.go b/pkg/sentry/fs/ext/ext.go
index 2604169de..10e235fb1 100644
--- a/pkg/sentry/fs/ext/ext.go
+++ b/pkg/sentry/fs/ext/ext.go
@@ -20,7 +20,6 @@ import (
 	"fmt"
 	"io"
 	"os"
-	"sync"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/sentry/context"
@@ -36,48 +35,6 @@ type filesystemType struct{}
 // Compiles only if filesystemType implements vfs.FilesystemType.
 var _ vfs.FilesystemType = (*filesystemType)(nil)
 
-// 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)
-
 // getDeviceFd returns the read seeker to the underlying device.
 // Currently there are two ways of mounting an ext(2/3/4) fs:
 //   1. Specify a mount with our internal special MountType in the OCI spec.
@@ -138,21 +95,3 @@ func (fstype filesystemType) NewFilesystem(ctx context.Context, creds *auth.Cred
 
 	return &fs.vfsfs, &newDentry(rootInode).vfsd, 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
-}
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
+}