ext: boilerplate code.

Renamed ext4 to ext since we are targeting ext(2/3/4).
Removed fs.go since we are targeting VFS2.
Added ext.go with filesystem struct.

PiperOrigin-RevId: 257689775

24 files changed, 62 insertions, 76 deletions

diff --git a/pkg/sentry/fs/ext/BUILD b/pkg/sentry/fs/ext/BUILD
new file mode 100644
index 000000000..3c2a02eac
--- /dev/null
+++ b/pkg/sentry/fs/ext/BUILD
@@ -0,0 +1,11 @@
+package(licenses = ["notice"])
+
+load("//tools/go_stateify:defs.bzl", "go_library")
+
+go_library(
+    name = "ext",
+    srcs = ["ext.go"],
+    importpath = "gvisor.dev/gvisor/pkg/sentry/fs/ext",
+    visibility = ["//pkg/sentry:internal"],
+    deps = ["//pkg/sentry/fs/ext/disklayout"],
+)
diff --git a/pkg/sentry/fs/ext4/disklayout/BUILD b/pkg/sentry/fs/ext/disklayout/BUILD
index 2920bfb52..e4cb26645 100644
--- a/pkg/sentry/fs/ext4/disklayout/BUILD
+++ b/pkg/sentry/fs/ext/disklayout/BUILD
@@ -21,7 +21,8 @@ go_library(
         "superblock_old.go",
         "test_utils.go",
     ],
-    importpath = "gvisor.dev/gvisor/pkg/sentry/fs/ext4/disklayout",
+    importpath = "gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout",
+    visibility = ["//pkg/sentry:internal"],
     deps = [
         "//pkg/abi/linux",
         "//pkg/binary",
diff --git a/pkg/sentry/fs/ext4/disklayout/block_group.go b/pkg/sentry/fs/ext/disklayout/block_group.go
index 32ea3d97d..32ea3d97d 100644
--- a/pkg/sentry/fs/ext4/disklayout/block_group.go
+++ b/pkg/sentry/fs/ext/disklayout/block_group.go
diff --git a/pkg/sentry/fs/ext4/disklayout/block_group_32.go b/pkg/sentry/fs/ext/disklayout/block_group_32.go
index 3e16c76db..3e16c76db 100644
--- a/pkg/sentry/fs/ext4/disklayout/block_group_32.go
+++ b/pkg/sentry/fs/ext/disklayout/block_group_32.go
diff --git a/pkg/sentry/fs/ext4/disklayout/block_group_64.go b/pkg/sentry/fs/ext/disklayout/block_group_64.go
index 9a809197a..9a809197a 100644
--- a/pkg/sentry/fs/ext4/disklayout/block_group_64.go
+++ b/pkg/sentry/fs/ext/disklayout/block_group_64.go
diff --git a/pkg/sentry/fs/ext4/disklayout/block_group_test.go b/pkg/sentry/fs/ext/disklayout/block_group_test.go
index 0ef4294c0..0ef4294c0 100644
--- a/pkg/sentry/fs/ext4/disklayout/block_group_test.go
+++ b/pkg/sentry/fs/ext/disklayout/block_group_test.go
diff --git a/pkg/sentry/fs/ext4/disklayout/dirent.go b/pkg/sentry/fs/ext/disklayout/dirent.go
index 685bf57b8..685bf57b8 100644
--- a/pkg/sentry/fs/ext4/disklayout/dirent.go
+++ b/pkg/sentry/fs/ext/disklayout/dirent.go
diff --git a/pkg/sentry/fs/ext4/disklayout/dirent_new.go b/pkg/sentry/fs/ext/disklayout/dirent_new.go
index 29ae4a5c2..29ae4a5c2 100644
--- a/pkg/sentry/fs/ext4/disklayout/dirent_new.go
+++ b/pkg/sentry/fs/ext/disklayout/dirent_new.go
diff --git a/pkg/sentry/fs/ext4/disklayout/dirent_old.go b/pkg/sentry/fs/ext/disklayout/dirent_old.go
index 2e0f9c812..2e0f9c812 100644
--- a/pkg/sentry/fs/ext4/disklayout/dirent_old.go
+++ b/pkg/sentry/fs/ext/disklayout/dirent_old.go
diff --git a/pkg/sentry/fs/ext4/disklayout/dirent_test.go b/pkg/sentry/fs/ext/disklayout/dirent_test.go
index cc6dff2c9..cc6dff2c9 100644
--- a/pkg/sentry/fs/ext4/disklayout/dirent_test.go
+++ b/pkg/sentry/fs/ext/disklayout/dirent_test.go
diff --git a/pkg/sentry/fs/ext4/disklayout/disklayout.go b/pkg/sentry/fs/ext/disklayout/disklayout.go
index bdf4e2132..bdf4e2132 100644
--- a/pkg/sentry/fs/ext4/disklayout/disklayout.go
+++ b/pkg/sentry/fs/ext/disklayout/disklayout.go
diff --git a/pkg/sentry/fs/ext4/disklayout/inode.go b/pkg/sentry/fs/ext/disklayout/inode.go
index b48001910..b48001910 100644
--- a/pkg/sentry/fs/ext4/disklayout/inode.go
+++ b/pkg/sentry/fs/ext/disklayout/inode.go
diff --git a/pkg/sentry/fs/ext4/disklayout/inode_new.go b/pkg/sentry/fs/ext/disklayout/inode_new.go
index 4f5348372..4f5348372 100644
--- a/pkg/sentry/fs/ext4/disklayout/inode_new.go
+++ b/pkg/sentry/fs/ext/disklayout/inode_new.go
diff --git a/pkg/sentry/fs/ext4/disklayout/inode_old.go b/pkg/sentry/fs/ext/disklayout/inode_old.go
index dc4c9d8e4..dc4c9d8e4 100644
--- a/pkg/sentry/fs/ext4/disklayout/inode_old.go
+++ b/pkg/sentry/fs/ext/disklayout/inode_old.go
diff --git a/pkg/sentry/fs/ext4/disklayout/inode_test.go b/pkg/sentry/fs/ext/disklayout/inode_test.go
index 9cae9e4f0..9cae9e4f0 100644
--- a/pkg/sentry/fs/ext4/disklayout/inode_test.go
+++ b/pkg/sentry/fs/ext/disklayout/inode_test.go
diff --git a/pkg/sentry/fs/ext4/disklayout/superblock.go b/pkg/sentry/fs/ext/disklayout/superblock.go
index e4b8f46fb..e4b8f46fb 100644
--- a/pkg/sentry/fs/ext4/disklayout/superblock.go
+++ b/pkg/sentry/fs/ext/disklayout/superblock.go
diff --git a/pkg/sentry/fs/ext4/disklayout/superblock_32.go b/pkg/sentry/fs/ext/disklayout/superblock_32.go
index 587e4afaa..587e4afaa 100644
--- a/pkg/sentry/fs/ext4/disklayout/superblock_32.go
+++ b/pkg/sentry/fs/ext/disklayout/superblock_32.go
diff --git a/pkg/sentry/fs/ext4/disklayout/superblock_64.go b/pkg/sentry/fs/ext/disklayout/superblock_64.go
index a2c2278fb..a2c2278fb 100644
--- a/pkg/sentry/fs/ext4/disklayout/superblock_64.go
+++ b/pkg/sentry/fs/ext/disklayout/superblock_64.go
diff --git a/pkg/sentry/fs/ext4/disklayout/superblock_old.go b/pkg/sentry/fs/ext/disklayout/superblock_old.go
index c74953610..c74953610 100644
--- a/pkg/sentry/fs/ext4/disklayout/superblock_old.go
+++ b/pkg/sentry/fs/ext/disklayout/superblock_old.go
diff --git a/pkg/sentry/fs/ext4/disklayout/superblock_test.go b/pkg/sentry/fs/ext/disklayout/superblock_test.go
index 463b5ba21..463b5ba21 100644
--- a/pkg/sentry/fs/ext4/disklayout/superblock_test.go
+++ b/pkg/sentry/fs/ext/disklayout/superblock_test.go
diff --git a/pkg/sentry/fs/ext4/disklayout/test_utils.go b/pkg/sentry/fs/ext/disklayout/test_utils.go
index 9c63f04c0..9c63f04c0 100644
--- a/pkg/sentry/fs/ext4/disklayout/test_utils.go
+++ b/pkg/sentry/fs/ext/disklayout/test_utils.go
diff --git a/pkg/sentry/fs/ext/ext.go b/pkg/sentry/fs/ext/ext.go
new file mode 100644
index 000000000..7602e2bf0
--- /dev/null
+++ b/pkg/sentry/fs/ext/ext.go
@@ -0,0 +1,49 @@
+// 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 implements readonly ext(2/3/4) filesystems.
+package ext
+
+import (
+	"io"
+	"sync"
+
+	"gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout"
+)
+
+// Filesystem implements vfs.FilesystemImpl.
+type Filesystem struct {
+	// dev is the ReadSeeker for the underlying fs device and is protected by mu.
+	dev io.ReadSeeker
+
+	// mu synchronizes the usage of dev. The ext filesystems take locality into
+	// condsideration, i.e. data blocks of a file will tend to be placed 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.
+	mu sync.Mutex
+
+	// 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
+}
diff --git a/pkg/sentry/fs/ext4/BUILD b/pkg/sentry/fs/ext4/BUILD
deleted file mode 100644
index 9dce67635..000000000
--- a/pkg/sentry/fs/ext4/BUILD
+++ /dev/null
@@ -1,14 +0,0 @@
-package(licenses = ["notice"])
-
-load("//tools/go_stateify:defs.bzl", "go_library")
-
-go_library(
-    name = "ext4",
-    srcs = ["fs.go"],
-    importpath = "gvisor.dev/gvisor/pkg/sentry/fs/ext4",
-    visibility = ["//pkg/sentry:internal"],
-    deps = [
-        "//pkg/sentry/context",
-        "//pkg/sentry/fs",
-    ],
-)
diff --git a/pkg/sentry/fs/ext4/fs.go b/pkg/sentry/fs/ext4/fs.go
deleted file mode 100644
index 5c7274821..000000000
--- a/pkg/sentry/fs/ext4/fs.go
+++ /dev/null
@@ -1,61 +0,0 @@
-// 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 ext4 implements the ext4 filesystem.
-package ext4
-
-import (
-	"gvisor.dev/gvisor/pkg/sentry/context"
-	"gvisor.dev/gvisor/pkg/sentry/fs"
-)
-
-// filesystem implements fs.Filesystem for ext4.
-//
-// +stateify savable
-type filesystem struct{}
-
-func init() {
-	fs.RegisterFilesystem(&filesystem{})
-}
-
-// FilesystemName is the name under which the filesystem is registered.
-// Name matches fs/ext4/super.c:ext4_fs_type.name.
-const FilesystemName = "ext4"
-
-// Name is the name of the file system.
-func (*filesystem) Name() string {
-	return FilesystemName
-}
-
-// AllowUserMount prohibits users from using mount(2) with this file system.
-func (*filesystem) AllowUserMount() bool {
-	return false
-}
-
-// AllowUserList prohibits this filesystem to be listed in /proc/filesystems.
-func (*filesystem) AllowUserList() bool {
-	return false
-}
-
-// Flags returns properties of the filesystem.
-//
-// In Linux, ext4 returns FS_REQUIRES_DEV. See fs/ext4/super.c
-func (*filesystem) Flags() fs.FilesystemFlags {
-	return fs.FilesystemRequiresDev
-}
-
-// Mount returns the root inode of the ext4 fs.
-func (f *filesystem) Mount(ctx context.Context, device string, flags fs.MountSourceFlags, data string, cgroupsInt interface{}) (*fs.Inode, error) {
-	panic("unimplemented")
-}