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authorAyush Ranjan <ayushranjan@google.com>2019-07-17 14:46:57 -0700
committergVisor bot <gvisor-bot@google.com>2019-07-17 14:48:04 -0700
commit8e3e021aca89427381af75a47f19b1fe78bf132e (patch)
tree030a8863bf5dace84d5aac3ea8e5063645837893 /pkg/sentry/fs
parent609cd91e3fc3359af263b52f494116ddbc800f77 (diff)
ext: Filesystem init implementation.
PiperOrigin-RevId: 258645957
Diffstat (limited to 'pkg/sentry/fs')
-rw-r--r--pkg/sentry/fs/ext/BUILD11
-rw-r--r--pkg/sentry/fs/ext/disklayout/block_group.go10
-rw-r--r--pkg/sentry/fs/ext/disklayout/superblock.go9
-rw-r--r--pkg/sentry/fs/ext/disklayout/superblock_old.go3
-rw-r--r--pkg/sentry/fs/ext/ext.go26
-rw-r--r--pkg/sentry/fs/ext/utils.go103
6 files changed, 157 insertions, 5 deletions
diff --git a/pkg/sentry/fs/ext/BUILD b/pkg/sentry/fs/ext/BUILD
index 3c2a02eac..b386f31c8 100644
--- a/pkg/sentry/fs/ext/BUILD
+++ b/pkg/sentry/fs/ext/BUILD
@@ -4,8 +4,15 @@ load("//tools/go_stateify:defs.bzl", "go_library")
go_library(
name = "ext",
- srcs = ["ext.go"],
+ srcs = [
+ "ext.go",
+ "utils.go",
+ ],
importpath = "gvisor.dev/gvisor/pkg/sentry/fs/ext",
visibility = ["//pkg/sentry:internal"],
- deps = ["//pkg/sentry/fs/ext/disklayout"],
+ deps = [
+ "//pkg/abi/linux",
+ "//pkg/sentry/fs/ext/disklayout",
+ "//pkg/syserror",
+ ],
)
diff --git a/pkg/sentry/fs/ext/disklayout/block_group.go b/pkg/sentry/fs/ext/disklayout/block_group.go
index 32ea3d97d..ad6f4fef8 100644
--- a/pkg/sentry/fs/ext/disklayout/block_group.go
+++ b/pkg/sentry/fs/ext/disklayout/block_group.go
@@ -18,6 +18,16 @@ package disklayout
// is split into a series of block groups. This provides an access layer to
// information needed to access and use a block group.
//
+// Location:
+// - The block group descriptor table is always placed in the blocks
+// immediately after the block containing the superblock.
+// - The 1st block group descriptor in the original table is in the
+// (sb.FirstDataBlock() + 1)th block.
+// - See SuperBlock docs to see where the block group descriptor table is
+// replicated.
+// - sb.BgDescSize() must be used as the block group descriptor entry size
+// while reading the table from disk.
+//
// See https://www.kernel.org/doc/html/latest/filesystems/ext4/globals.html#block-group-descriptors.
type BlockGroup interface {
// InodeTable returns the absolute block number of the block containing the
diff --git a/pkg/sentry/fs/ext/disklayout/superblock.go b/pkg/sentry/fs/ext/disklayout/superblock.go
index e4b8f46fb..7a337a5e0 100644
--- a/pkg/sentry/fs/ext/disklayout/superblock.go
+++ b/pkg/sentry/fs/ext/disklayout/superblock.go
@@ -14,6 +14,11 @@
package disklayout
+const (
+ // SbOffset is the absolute offset at which the superblock is placed.
+ SbOffset = 1024
+)
+
// SuperBlock should be implemented by structs representing the ext superblock.
// The superblock holds a lot of information about the enclosing filesystem.
// This interface aims to provide access methods to important information held
@@ -57,8 +62,6 @@ type SuperBlock interface {
//
// If the filesystem has 1kb data blocks then this should return 1. For all
// other configurations, this typically returns 0.
- //
- // The first block group descriptor is in (FirstDataBlock() + 1)th block.
FirstDataBlock() uint32
// BlockSize returns the size of one data block in this filesystem.
@@ -128,7 +131,7 @@ type SuperBlock interface {
}
// SbRevision is the type for superblock revisions.
-type SbRevision int
+type SbRevision uint32
// Super block revisions.
const (
diff --git a/pkg/sentry/fs/ext/disklayout/superblock_old.go b/pkg/sentry/fs/ext/disklayout/superblock_old.go
index c74953610..aada8b550 100644
--- a/pkg/sentry/fs/ext/disklayout/superblock_old.go
+++ b/pkg/sentry/fs/ext/disklayout/superblock_old.go
@@ -44,6 +44,9 @@ type SuperBlockOld struct {
DefResGID uint16
}
+// Compiles only if SuperBlockOld implements SuperBlock.
+var _ SuperBlock = (*SuperBlockOld)(nil)
+
// InodesCount implements SuperBlock.InodesCount.
func (sb *SuperBlockOld) InodesCount() uint32 { return sb.InodesCountRaw }
diff --git a/pkg/sentry/fs/ext/ext.go b/pkg/sentry/fs/ext/ext.go
index 7602e2bf0..9d33be08f 100644
--- a/pkg/sentry/fs/ext/ext.go
+++ b/pkg/sentry/fs/ext/ext.go
@@ -19,7 +19,9 @@ import (
"io"
"sync"
+ "gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout"
+ "gvisor.dev/gvisor/pkg/syserror"
)
// Filesystem implements vfs.FilesystemImpl.
@@ -47,3 +49,27 @@ type Filesystem struct {
// Immutable after initialization.
bgs []disklayout.BlockGroup
}
+
+// newFilesystem is the Filesystem constructor.
+func newFilesystem(dev io.ReadSeeker) (*Filesystem, error) {
+ fs := Filesystem{dev: dev}
+ var err error
+
+ fs.sb, err = readSuperBlock(dev)
+ if err != nil {
+ return 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
+ }
+
+ fs.bgs, err = readBlockGroups(dev, fs.sb)
+ if err != nil {
+ return nil, err
+ }
+
+ return &fs, nil
+}
diff --git a/pkg/sentry/fs/ext/utils.go b/pkg/sentry/fs/ext/utils.go
new file mode 100644
index 000000000..861ef9a73
--- /dev/null
+++ b/pkg/sentry/fs/ext/utils.go
@@ -0,0 +1,103 @@
+// 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 (
+ "encoding/binary"
+ "io"
+
+ "gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout"
+ "gvisor.dev/gvisor/pkg/syserror"
+)
+
+// readFromDisk performs a binary read from disk into the given struct from
+// the absolute offset provided.
+//
+// All disk reads should use this helper so we avoid reading from stale
+// previously used offsets. This function forces the offset parameter.
+func readFromDisk(dev io.ReadSeeker, abOff int64, v interface{}) error {
+ if _, err := dev.Seek(abOff, io.SeekStart); err != nil {
+ return syserror.EIO
+ }
+
+ if err := binary.Read(dev, binary.LittleEndian, v); err != nil {
+ return syserror.EIO
+ }
+
+ return nil
+}
+
+// readSuperBlock reads the SuperBlock from block group 0 in the underlying
+// device. There are three versions of the superblock. This function identifies
+// and returns the correct version.
+func readSuperBlock(dev io.ReadSeeker) (disklayout.SuperBlock, error) {
+ var sb disklayout.SuperBlock = &disklayout.SuperBlockOld{}
+ if err := readFromDisk(dev, disklayout.SbOffset, sb); err != nil {
+ return nil, err
+ }
+ if sb.Revision() == disklayout.OldRev {
+ return sb, nil
+ }
+
+ sb = &disklayout.SuperBlock32Bit{}
+ if err := readFromDisk(dev, disklayout.SbOffset, sb); err != nil {
+ return nil, err
+ }
+ if !sb.IncompatibleFeatures().Is64Bit {
+ return sb, nil
+ }
+
+ sb = &disklayout.SuperBlock64Bit{}
+ if err := readFromDisk(dev, disklayout.SbOffset, sb); err != nil {
+ return nil, err
+ }
+ return sb, nil
+}
+
+// blockGroupsCount returns the number of block groups in the ext fs.
+func blockGroupsCount(sb disklayout.SuperBlock) uint64 {
+ blocksCount := sb.BlocksCount()
+ blocksPerGroup := uint64(sb.BlocksPerGroup())
+
+ // Round up the result. float64 can compromise precision so do it manually.
+ bgCount := blocksCount / blocksPerGroup
+ if blocksCount%blocksPerGroup != 0 {
+ bgCount++
+ }
+
+ return bgCount
+}
+
+// readBlockGroups reads the block group descriptor table from block group 0 in
+// the underlying device.
+func readBlockGroups(dev io.ReadSeeker, sb disklayout.SuperBlock) ([]disklayout.BlockGroup, error) {
+ bgCount := blockGroupsCount(sb)
+ bgdSize := uint64(sb.BgDescSize())
+ is64Bit := sb.IncompatibleFeatures().Is64Bit
+ bgds := make([]disklayout.BlockGroup, bgCount)
+
+ for i, off := uint64(0), uint64(sb.FirstDataBlock()+1)*sb.BlockSize(); i < bgCount; i, off = i+1, off+bgdSize {
+ if is64Bit {
+ bgds[i] = &disklayout.BlockGroup64Bit{}
+ } else {
+ bgds[i] = &disklayout.BlockGroup32Bit{}
+ }
+
+ if err := readFromDisk(dev, int64(off), bgds[i]); err != nil {
+ return nil, err
+ }
+ }
+ return bgds, nil
+}