Superblock interface in the disk layout package for ext4.

PiperOrigin-RevId: 255644277

3 files changed, 472 insertions, 3 deletions

diff --git a/pkg/sentry/fs/ext4/disklayout/BUILD b/pkg/sentry/fs/ext4/disklayout/BUILD
index 2fb1d5b37..be637bcbb 100644
--- a/pkg/sentry/fs/ext4/disklayout/BUILD
+++ b/pkg/sentry/fs/ext4/disklayout/BUILD
@@ -8,6 +8,7 @@ go_library(
         "block_group.go",
         "block_group_32.go",
         "block_group_64.go",
+        "superblock.go",
     ],
     importpath = "gvisor.dev/gvisor/pkg/sentry/fs/ext4/disklayout",
 )
diff --git a/pkg/sentry/fs/ext4/disklayout/block_group.go b/pkg/sentry/fs/ext4/disklayout/block_group.go
index 7359df5b9..7df76a036 100644
--- a/pkg/sentry/fs/ext4/disklayout/block_group.go
+++ b/pkg/sentry/fs/ext4/disklayout/block_group.go
@@ -128,8 +128,8 @@ func (f BGFlags) ToInt() uint16 {
 // BGFlagsFromInt converts the 16-bit flag representation to a BGFlags struct.
 func BGFlagsFromInt(flags uint16) BGFlags {
 	return BGFlags{
-		InodeUninit: (flags & BgInodeUninit) > 0,
-		BlockUninit: (flags & BgBlockUninit) > 0,
-		InodeZeroed: (flags & BgInodeZeroed) > 0,
+		InodeUninit: flags&BgInodeUninit > 0,
+		BlockUninit: flags&BgBlockUninit > 0,
+		InodeZeroed: flags&BgInodeZeroed > 0,
 	}
 }
diff --git a/pkg/sentry/fs/ext4/disklayout/superblock.go b/pkg/sentry/fs/ext4/disklayout/superblock.go
new file mode 100644
index 000000000..d630ba8a6
--- /dev/null
+++ b/pkg/sentry/fs/ext4/disklayout/superblock.go
@@ -0,0 +1,468 @@
+// 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 disklayout
+
+// SuperBlock should be implemented by structs representing ext4 superblock.
+// The superblock holds a lot of information about the enclosing filesystem.
+// This interface aims to provide access methods to important information held
+// by the superblock. It does NOT expose all fields of the superblock, only the
+// ones necessary. This can be expanded when need be.
+//
+// Location and replication:
+//     - The superblock is located at offset 1024 in block group 0.
+//     - Redundant copies of the superblock and group descriptors are kept in
+//       all groups if sparse_super feature flag is NOT set. If it is set, the
+//       replicas only exist in groups whose group number is either 0 or a
+//       power of 3, 5, or 7.
+//     - There is also a sparse superblock feature v2 in which there are just
+//       two replicas saved in block groups pointed by the s_backup_bgs field.
+//
+// Replicas should eventually be updated if the superblock is updated.
+//
+// See https://www.kernel.org/doc/html/latest/filesystems/ext4/globals.html#super-block.
+type SuperBlock interface {
+	// InodesCount returns the total number of inodes in this filesystem.
+	InodesCount() uint32
+
+	// BlocksCount returns the total number of data blocks in this filesystem.
+	BlocksCount() uint64
+
+	// FreeBlocksCount returns the number of free blocks in this filesystem.
+	FreeBlocksCount() uint64
+
+	// FreeInodesCount returns the number of free inodes in this filesystem.
+	FreeInodesCount() uint32
+
+	// MountCount returns the number of mounts since the last fsck.
+	MountCount() uint16
+
+	// MaxMountCount returns the number of mounts allowed beyond which a fsck is
+	// needed.
+	MaxMountCount() uint16
+
+	// FirstDataBlock returns the absolute block number of the first data block,
+	// which contains the super block itself.
+	//
+	// 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.
+	// This can be calculated by 2^(10 + sb.s_log_block_size). This ensures that
+	// the smallest block size is 1kb.
+	BlockSize() uint64
+
+	// BlocksPerGroup returns the number of data blocks in a block group.
+	BlocksPerGroup() uint32
+
+	// ClusterSize returns block cluster size (set during mkfs time by admin).
+	// This can be calculated by 2^(10 + sb.s_log_cluster_size). This ensures that
+	// the smallest cluster size is 1kb.
+	//
+	// sb.s_log_cluster_size must equal sb.s_log_block_size if bigalloc feature
+	// is NOT set and consequently BlockSize() = ClusterSize() in that case.
+	ClusterSize() uint64
+
+	// ClustersPerGroup returns:
+	//     - number of clusters per group        if bigalloc is enabled.
+	//     - BlocksPerGroup()                    otherwise.
+	ClustersPerGroup() uint32
+
+	// InodeSize returns the size of the inode disk record size in bytes. Use this
+	// to iterate over inode arrays on disk.
+	//
+	// In ext2 and ext3:
+	//     - Each inode had a disk record of 128 bytes.
+	//     - The inode struct size was fixed at 128 bytes.
+	//
+	// In ext4 its possible to allocate larger on-disk inodes:
+	//     - Inode disk record size = sb.s_inode_size (function return value).
+	//                              = 256 (default)
+	//     - Inode struct size = 128 + inode.i_extra_isize.
+	//                         = 128 + 28 = 156 (default)
+	InodeSize() uint16
+
+	// InodesPerGroup returns the number of inodes in a block group.
+	InodesPerGroup() uint32
+
+	// BgDescSize returns the size of the block group descriptor struct.
+	//
+	// In ext2, ext3, ext4 (without 64-bit feature), the block group descriptor
+	// is only 32 bytes long.
+	// In ext4 with 64-bit feature, the block group descriptor expands to AT LEAST
+	// 64 bytes. It might be bigger than that.
+	BgDescSize() uint16
+
+	// CompatibleFeatures returns the CompatFeatures struct which holds all the
+	// compatible features this fs supports.
+	CompatibleFeatures() CompatFeatures
+
+	// IncompatibleFeatures returns the CompatFeatures struct which holds all the
+	// incompatible features this fs supports.
+	IncompatibleFeatures() IncompatFeatures
+
+	// ReadOnlyCompatibleFeatures returns the CompatFeatures struct which holds all the
+	// readonly compatible features this fs supports.
+	ReadOnlyCompatibleFeatures() RoCompatFeatures
+
+	// Magic() returns the magic signature which must be 0xef53.
+	Magic() uint16
+
+	// Revision returns the superblock revision. Superblock struct fields from
+	// offset 0x54 till 0x150 should only be used if superblock has DynamicRev.
+	Revision() SbRevision
+}
+
+// SbRevision is the type for superblock revisions.
+type SbRevision int
+
+// Super block revisions.
+const (
+	// OldRev is the good old (original) format.
+	OldRev SbRevision = 0
+
+	// DynamicRev is v2 format w/ dynamic inode sizes.
+	DynamicRev SbRevision = 1
+)
+
+// Superblock compatible features.
+// This is not exhaustive, unused features are not listed.
+const (
+	// SbDirPrealloc indicates directory preallocation.
+	SbDirPrealloc = 0x1
+
+	// SbHasJournal indicates the presence of a journal. jbd2 should only work
+	// with this being set.
+	SbHasJournal = 0x4
+
+	// SbExtAttr indicates extended attributes support.
+	SbExtAttr = 0x8
+
+	// SbResizeInode indicates that the fs has reserved GDT blocks (right after
+	// group descriptors) for fs expansion.
+	SbResizeInode = 0x10
+
+	// SbDirIndex indicates that the fs has directory indices.
+	SbDirIndex = 0x20
+
+	// SbSparseV2 stands for Sparse superblock version 2.
+	SbSparseV2 = 0x200
+)
+
+// CompatFeatures represents a superblock's compatible feature set. If the
+// kernel does not understand any of these feature, it can still read/write
+// to this fs.
+type CompatFeatures struct {
+	DirPrealloc bool
+	HasJournal  bool
+	ExtAttr     bool
+	ResizeInode bool
+	DirIndex    bool
+	SparseV2    bool
+}
+
+// ToInt converts superblock compatible features back to its 32-bit rep.
+func (f CompatFeatures) ToInt() uint32 {
+	var res uint32
+
+	if f.DirPrealloc {
+		res |= SbDirPrealloc
+	}
+	if f.HasJournal {
+		res |= SbHasJournal
+	}
+	if f.ExtAttr {
+		res |= SbExtAttr
+	}
+	if f.ResizeInode {
+		res |= SbResizeInode
+	}
+	if f.DirIndex {
+		res |= SbDirIndex
+	}
+	if f.SparseV2 {
+		res |= SbSparseV2
+	}
+
+	return res
+}
+
+// CompatFeaturesFromInt converts the integer representation of superblock
+// compatible features to CompatFeatures struct.
+func CompatFeaturesFromInt(f uint32) CompatFeatures {
+	return CompatFeatures{
+		DirPrealloc: f&SbDirPrealloc > 0,
+		HasJournal:  f&SbHasJournal > 0,
+		ExtAttr:     f&SbExtAttr > 0,
+		ResizeInode: f&SbResizeInode > 0,
+		DirIndex:    f&SbDirIndex > 0,
+		SparseV2:    f&SbSparseV2 > 0,
+	}
+}
+
+// Superblock incompatible features.
+// This is not exhaustive, unused features are not listed.
+const (
+	// SbDirentFileType indicates that directory entries record the file type.
+	// We should use struct ext4_dir_entry_2 for dirents then.
+	SbDirentFileType = 0x2
+
+	// SbRecovery indicates that the filesystem needs recovery.
+	SbRecovery = 0x4
+
+	// SbJournalDev indicates that the filesystem has a separate journal device.
+	SbJournalDev = 0x8
+
+	// SbMetaBG indicates that the filesystem is using Meta block groups. Moves
+	// the group descriptors from the congested first block group into the first
+	// group of each metablock group to increase the maximum block groups limit
+	// and hence support much larger filesystems.
+	//
+	// See https://www.kernel.org/doc/html/latest/filesystems/ext4/overview.html#meta-block-groups.
+	SbMetaBG = 0x10
+
+	// SbExtents indicates that the filesystem uses extents. Must be set in ext4
+	// filesystems.
+	SbExtents = 0x40
+
+	// SbIs64Bit indicates that this filesystem addresses blocks with 64-bits.
+	// Hence can support 2^64 data blocks.
+	SbIs64Bit = 0x80
+
+	// SbMMP indicates that this filesystem has multiple mount protection.
+	//
+	// See https://www.kernel.org/doc/html/latest/filesystems/ext4/globals.html#multiple-mount-protection.
+	SbMMP = 0x100
+
+	// SbFlexBg indicates that this filesystem has flexible block groups. Several
+	// block groups are tied into one logical block group so that all the metadata
+	// for the block groups (bitmaps and inode tables) are close together for
+	// faster loading. Consequently, large files will be continuous on disk.
+	// However, this does not affect the placement of redundant superblocks and
+	// group descriptors.
+	//
+	// See https://www.kernel.org/doc/html/latest/filesystems/ext4/overview.html#flexible-block-groups.
+	SbFlexBg = 0x200
+
+	// SbLargeDir shows that large directory enabled. Directory htree can be 3
+	// levels deep. Directory htrees are allowed to be 2 levels deep otherwise.
+	SbLargeDir = 0x4000
+
+	// SbInlineData allows inline data in inodes for really small files.
+	SbInlineData = 0x8000
+
+	// SbEncrypted indicates that this fs contains encrypted inodes.
+	SbEncrypted = 0x10000
+)
+
+// IncompatFeatures represents a superblock's incompatible feature set. If the
+// kernel does not understand any of these feature, it should refuse to mount.
+type IncompatFeatures struct {
+	DirentFileType bool
+	Recovery       bool
+	JournalDev     bool
+	MetaBG         bool
+	Extents        bool
+	Is64Bit        bool
+	MMP            bool
+	FlexBg         bool
+	LargeDir       bool
+	InlineData     bool
+	Encrypted      bool
+}
+
+// ToInt converts superblock incompatible features back to its 32-bit rep.
+func (f IncompatFeatures) ToInt() uint32 {
+	var res uint32
+
+	if f.DirentFileType {
+		res |= SbDirentFileType
+	}
+	if f.Recovery {
+		res |= SbRecovery
+	}
+	if f.JournalDev {
+		res |= SbJournalDev
+	}
+	if f.MetaBG {
+		res |= SbMetaBG
+	}
+	if f.Extents {
+		res |= SbExtents
+	}
+	if f.Is64Bit {
+		res |= SbIs64Bit
+	}
+	if f.MMP {
+		res |= SbMMP
+	}
+	if f.FlexBg {
+		res |= SbFlexBg
+	}
+	if f.LargeDir {
+		res |= SbLargeDir
+	}
+	if f.InlineData {
+		res |= SbInlineData
+	}
+	if f.Encrypted {
+		res |= SbEncrypted
+	}
+
+	return res
+}
+
+// IncompatFeaturesFromInt converts the integer representation of superblock
+// incompatible features to IncompatFeatures struct.
+func IncompatFeaturesFromInt(f uint32) IncompatFeatures {
+	return IncompatFeatures{
+		DirentFileType: f&SbDirentFileType > 0,
+		Recovery:       f&SbRecovery > 0,
+		JournalDev:     f&SbJournalDev > 0,
+		MetaBG:         f&SbMetaBG > 0,
+		Extents:        f&SbExtents > 0,
+		Is64Bit:        f&SbIs64Bit > 0,
+		MMP:            f&SbMMP > 0,
+		FlexBg:         f&SbFlexBg > 0,
+		LargeDir:       f&SbLargeDir > 0,
+		InlineData:     f&SbInlineData > 0,
+		Encrypted:      f&SbEncrypted > 0,
+	}
+}
+
+// Superblock readonly compatible features.
+// This is not exhaustive, unused features are not listed.
+const (
+	// SbSparse indicates sparse superblocks. Only groups with number either 0 or
+	// a power of 3, 5, or 7 will have redundant copies of the superblock and
+	// block descriptors.
+	SbSparse = 0x1
+
+	// SbLargeFile indicates that this fs has been used to store a file >= 2GiB.
+	SbLargeFile = 0x2
+
+	// SbHugeFile indicates that this fs contains files whose sizes are
+	// represented in units of logicals blocks, not 512-byte sectors.
+	SbHugeFile = 0x8
+
+	// SbGdtCsum indicates that group descriptors have checksums.
+	SbGdtCsum = 0x10
+
+	// SbDirNlink indicates that the new subdirectory limit is 64,999. Ext3 has a
+	// 32,000 subdirectory limit.
+	SbDirNlink = 0x20
+
+	// SbExtraIsize indicates that large inodes exist on this filesystem.
+	SbExtraIsize = 0x40
+
+	// SbHasSnapshot indicates the existence of a snapshot.
+	SbHasSnapshot = 0x80
+
+	// SbQuota enables usage tracking for all quota types.
+	SbQuota = 0x100
+
+	// SbBigalloc maps to the bigalloc feature. When set, the minimum allocation
+	// unit becomes a cluster rather than a data block. Then block bitmaps track
+	// clusters, not data blocks.
+	//
+	// See https://www.kernel.org/doc/html/latest/filesystems/ext4/overview.html#bigalloc.
+	SbBigalloc = 0x200
+
+	// SbMetadataCsum indicates that the fs supports metadata checksumming.
+	SbMetadataCsum = 0x400
+
+	// SbReadOnly marks this filesystem as readonly. Should refuse to mount in
+	// read/write mode.
+	SbReadOnly = 0x1000
+)
+
+// RoCompatFeatures represents a superblock's readonly compatible feature set.
+// If the kernel does not understand any of these feature, it can still mount
+// readonly. But if the user wants to mount read/write, the kernel should
+// refuse to mount.
+type RoCompatFeatures struct {
+	Sparse       bool
+	LargeFile    bool
+	HugeFile     bool
+	GdtCsum      bool
+	DirNlink     bool
+	ExtraIsize   bool
+	HasSnapshot  bool
+	Quota        bool
+	Bigalloc     bool
+	MetadataCsum bool
+	ReadOnly     bool
+}
+
+// ToInt converts superblock readonly compatible features to its 32-bit rep.
+func (f RoCompatFeatures) ToInt() uint32 {
+	var res uint32
+
+	if f.Sparse {
+		res |= SbSparse
+	}
+	if f.LargeFile {
+		res |= SbLargeFile
+	}
+	if f.HugeFile {
+		res |= SbHugeFile
+	}
+	if f.GdtCsum {
+		res |= SbGdtCsum
+	}
+	if f.DirNlink {
+		res |= SbDirNlink
+	}
+	if f.ExtraIsize {
+		res |= SbExtraIsize
+	}
+	if f.HasSnapshot {
+		res |= SbHasSnapshot
+	}
+	if f.Quota {
+		res |= SbQuota
+	}
+	if f.Bigalloc {
+		res |= SbBigalloc
+	}
+	if f.MetadataCsum {
+		res |= SbMetadataCsum
+	}
+	if f.ReadOnly {
+		res |= SbReadOnly
+	}
+
+	return res
+}
+
+// RoCompatFeaturesFromInt converts the integer representation of superblock
+// readonly compatible features to RoCompatFeatures struct.
+func RoCompatFeaturesFromInt(f uint32) RoCompatFeatures {
+	return RoCompatFeatures{
+		Sparse:       f&SbSparse > 0,
+		LargeFile:    f&SbLargeFile > 0,
+		HugeFile:     f&SbHugeFile > 0,
+		GdtCsum:      f&SbGdtCsum > 0,
+		DirNlink:     f&SbDirNlink > 0,
+		ExtraIsize:   f&SbExtraIsize > 0,
+		HasSnapshot:  f&SbHasSnapshot > 0,
+		Quota:        f&SbQuota > 0,
+		Bigalloc:     f&SbBigalloc > 0,
+		MetadataCsum: f&SbMetadataCsum > 0,
+		ReadOnly:     f&SbReadOnly > 0,
+	}
+}