ext: testing environment setup with VFS2 support.

PiperOrigin-RevId: 259835948

1 files changed, 61 insertions, 9 deletions

diff --git a/pkg/sentry/fs/ext/ext.go b/pkg/sentry/fs/ext/ext.go
index 7f4287b01..c8b554f4d 100644
--- a/pkg/sentry/fs/ext/ext.go
+++ b/pkg/sentry/fs/ext/ext.go
@@ -16,17 +16,34 @@
 package ext
 
 import (
+	"errors"
+	"fmt"
 	"io"
+	"os"
 	"sync"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/sentry/context"
 	"gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
 
+// filesystemType implements vfs.FilesystemType.
+type filesystemType struct{}
+
+// Compiles only if filesystemType implements vfs.FilesystemType.
+var _ vfs.FilesystemType = (*filesystemType)(nil)
+
 // filesystem implements vfs.FilesystemImpl.
 type filesystem struct {
-	// mu serializes changes to the Dentry tree and the usage of the read seeker.
+	// 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.
@@ -58,28 +75,63 @@ type filesystem struct {
 	bgs []disklayout.BlockGroup
 }
 
-// newFilesystem is the filesystem constructor.
-func newFilesystem(dev io.ReadSeeker) (*filesystem, error) {
-	fs := filesystem{dev: dev, inodeCache: make(map[uint32]*inode)}
-	var err error
+// 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.
+//   2. Expose the device to the container and mount it from application layer.
+func getDeviceFd(source string, opts vfs.NewFilesystemOptions) (io.ReadSeeker, error) {
+	if opts.InternalData == nil {
+		// User mount call.
+		// TODO(b/134676337): Open the device specified by `source` and return that.
+		panic("unimplemented")
+	}
+
+	// NewFilesystem call originated from within the sentry.
+	fd, ok := opts.InternalData.(uintptr)
+	if !ok {
+		return nil, errors.New("internal data for ext fs must be a uintptr containing the file descriptor to device")
+	}
+
+	// We do not close this file because that would close the underlying device
+	// file descriptor (which is required for reading the fs from disk).
+	// TODO(b/134676337): Use pkg/fd instead.
+	deviceFile := os.NewFile(fd, source)
+	if deviceFile == nil {
+		return nil, fmt.Errorf("ext4 device file descriptor is not valid: %d", fd)
+	}
+
+	return deviceFile, nil
+}
 
+// NewFilesystem implements vfs.FilesystemType.NewFilesystem.
+func (fstype filesystemType) NewFilesystem(ctx context.Context, creds *auth.Credentials, source string, opts vfs.NewFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
+	dev, err := getDeviceFd(source, opts)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	fs := filesystem{dev: dev, inodeCache: make(map[uint32]*inode)}
+	fs.vfsfs.Init(&fs)
 	fs.sb, err = readSuperBlock(dev)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 
 	if fs.sb.Magic() != linux.EXT_SUPER_MAGIC {
 		// mount(2) specifies that EINVAL should be returned if the superblock is
 		// invalid.
-		return nil, syserror.EINVAL
+		return nil, nil, syserror.EINVAL
 	}
 
 	fs.bgs, err = readBlockGroups(dev, fs.sb)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 
-	return &fs, nil
+	return &fs.vfsfs, nil, nil
 }
 
 // getOrCreateInode gets the inode corresponding to the inode number passed in.