ext4 block group descriptor implementation in disk layout package.
PiperOrigin-RevId: 254482180
This commit is contained in:
Ayush Ranjan
gVisor bot
parent
e806466fc5
commit
727375321f
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package(licenses = ["notice"])
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load("//tools/go_stateify:defs.bzl", "go_library", "go_test")
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go_library(
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name = "disklayout",
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srcs = [
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"block_group.go",
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"block_group_32.go",
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"block_group_64.go",
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],
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importpath = "gvisor.dev/gvisor/pkg/sentry/fs/ext4/disklayout",
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)
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go_test(
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name = "disklayout_test",
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size = "small",
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srcs = ["block_group_test.go"],
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embed = [":disklayout"],
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deps = ["//pkg/binary"],
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)
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// Copyright 2019 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package disklayout provides ext4 disk level structures which can be directly
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// filled with bytes from the underlying device. All structures on disk are in
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// little-endian order. Only jbd2 (journal) structures are in big-endian order.
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// Structs aim to emulate structures `exactly` how they are layed out on disk.
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//
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// Note: All fields in these structs are exported because binary.Read would
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// panic otherwise.
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package disklayout
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// BlockGroup represents Linux struct ext4_group_desc which is internally
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// called a block group descriptor. An ext4 file system is split into a series
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// of block groups. This provides an access layer to information needed to
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// access and use a block group.
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//
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// See https://www.kernel.org/doc/html/latest/filesystems/ext4/globals.html#block-group-descriptors.
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type BlockGroup interface {
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// InodeTable returns the absolute block number of the block containing the
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// inode table. This points to an array of Inode structs. Inode tables are
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// statically allocated at mkfs time. The superblock records the number of
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// inodes per group (length of this table).
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InodeTable() uint64
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// BlockBitmap returns the absolute block number of the block containing the
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// block bitmap. This bitmap tracks the usage of data blocks within this block
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// group and has its own checksum.
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BlockBitmap() uint64
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// InodeBitmap returns the absolute block number of the block containing the
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// inode bitmap. This bitmap tracks the usage of this group's inode table
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// entries and has its own checksum.
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InodeBitmap() uint64
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// ExclusionBitmap returns the absolute block number of the snapshot exclusion
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// bitmap.
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ExclusionBitmap() uint64
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// FreeBlocksCount returns the number of free blocks in the group.
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FreeBlocksCount() uint32
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// FreeInodesCount returns the number of free inodes in the group.
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FreeInodesCount() uint32
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// DirectoryCount returns the number of inodes that represent directories
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// under this block group.
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DirectoryCount() uint32
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// UnusedInodeCount returns the number of unused inodes beyond the last used
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// inode in this group's inode table. As a result, we needn’t scan past the
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// (InodesPerGroup - UnusedInodeCount())th entry in the inode table.
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UnusedInodeCount() uint32
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// BlockBitmapChecksum returns the block bitmap checksum. This is calculated
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// using crc32c(FS UUID + group number + entire bitmap).
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BlockBitmapChecksum() uint32
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// InodeBitmapChecksum returns the inode bitmap checksum. This is calculated
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// using crc32c(FS UUID + group number + entire bitmap).
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InodeBitmapChecksum() uint32
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// Checksum returns this block group's checksum.
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//
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// If RO_COMPAT_METADATA_CSUM feature is set:
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// - checksum is crc32c(FS UUID + group number + group descriptor
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// structure) & 0xFFFF.
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//
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// If RO_COMPAT_GDT_CSUM feature is set:
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// - checksum is crc16(FS UUID + group number + group descriptor
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// structure).
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//
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// RO_COMPAT_METADATA_CSUM and RO_COMPAT_GDT_CSUM should not be both set.
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// If they are, Linux warns and asks to run fsck.
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Checksum() uint16
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// Flags returns BGFlags which represents the block group flags.
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Flags() BGFlags
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}
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// These are the different block group flags.
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const (
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// BgInodeUninit indicates that inode table and bitmap are not initialized.
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BgInodeUninit uint16 = 0x1
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// BgBlockUninit indicates that block bitmap is not initialized.
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BgBlockUninit uint16 = 0x2
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// BgInodeZeroed indicates that inode table is zeroed.
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BgInodeZeroed uint16 = 0x4
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)
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// BGFlags represents all the different combinations of block group flags.
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type BGFlags struct {
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InodeUninit bool
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BlockUninit bool
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InodeZeroed bool
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}
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// ToInt converts a BGFlags struct back to its 16-bit representation.
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func (f BGFlags) ToInt() uint16 {
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var res uint16
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if f.InodeUninit {
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res |= BgInodeUninit
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}
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if f.BlockUninit {
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res |= BgBlockUninit
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}
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if f.InodeZeroed {
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res |= BgInodeZeroed
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}
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return res
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}
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// BGFlagsFromInt converts the 16-bit flag representation to a BGFlags struct.
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func BGFlagsFromInt(flags uint16) BGFlags {
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return BGFlags{
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InodeUninit: (flags & BgInodeUninit) > 0,
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BlockUninit: (flags & BgBlockUninit) > 0,
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InodeZeroed: (flags & BgInodeZeroed) > 0,
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}
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}
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// Copyright 2019 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package disklayout
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// BlockGroup32Bit emulates the first half of struct ext4_group_desc in
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// fs/ext4/ext4.h. It is the block group descriptor struct for 32-bit ext4
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// filesystems. It implements BlockGroup interface.
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//
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// The suffix `Lo` here stands for lower bits because this is also used in the
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// 64-bit version where these fields represent the lower half of the fields.
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// The suffix `Raw` has been added to indicate that the field does not have a
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// counterpart in the 64-bit version and to resolve name collision with the
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// interface.
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type BlockGroup32Bit struct {
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BlockBitmapLo uint32
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InodeBitmapLo uint32
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InodeTableLo uint32
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FreeBlocksCountLo uint16
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FreeInodesCountLo uint16
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UsedDirsCountLo uint16
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FlagsRaw uint16
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ExcludeBitmapLo uint32
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BlockBitmapChecksumLo uint16
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InodeBitmapChecksumLo uint16
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ItableUnusedLo uint16
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ChecksumRaw uint16
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}
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// InodeTable implements BlockGroup.InodeTable.
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func (bg *BlockGroup32Bit) InodeTable() uint64 { return uint64(bg.InodeTableLo) }
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// BlockBitmap implements BlockGroup.BlockBitmap.
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func (bg *BlockGroup32Bit) BlockBitmap() uint64 { return uint64(bg.BlockBitmapLo) }
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// InodeBitmap implements BlockGroup.InodeBitmap.
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func (bg *BlockGroup32Bit) InodeBitmap() uint64 { return uint64(bg.InodeBitmapLo) }
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// ExclusionBitmap implements BlockGroup.ExclusionBitmap.
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func (bg *BlockGroup32Bit) ExclusionBitmap() uint64 { return uint64(bg.ExcludeBitmapLo) }
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// FreeBlocksCount implements BlockGroup.FreeBlocksCount.
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func (bg *BlockGroup32Bit) FreeBlocksCount() uint32 { return uint32(bg.FreeBlocksCountLo) }
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// FreeInodesCount implements BlockGroup.FreeInodesCount.
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func (bg *BlockGroup32Bit) FreeInodesCount() uint32 { return uint32(bg.FreeInodesCountLo) }
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// DirectoryCount implements BlockGroup.DirectoryCount.
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func (bg *BlockGroup32Bit) DirectoryCount() uint32 { return uint32(bg.UsedDirsCountLo) }
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// UnusedInodeCount implements BlockGroup.UnusedInodeCount.
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func (bg *BlockGroup32Bit) UnusedInodeCount() uint32 { return uint32(bg.ItableUnusedLo) }
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// BlockBitmapChecksum implements BlockGroup.BlockBitmapChecksum.
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func (bg *BlockGroup32Bit) BlockBitmapChecksum() uint32 { return uint32(bg.BlockBitmapChecksumLo) }
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// InodeBitmapChecksum implements BlockGroup.InodeBitmapChecksum.
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func (bg *BlockGroup32Bit) InodeBitmapChecksum() uint32 { return uint32(bg.InodeBitmapChecksumLo) }
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// Checksum implements BlockGroup.Checksum.
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func (bg *BlockGroup32Bit) Checksum() uint16 { return bg.ChecksumRaw }
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// Flags implements BlockGroup.Flags.
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func (bg *BlockGroup32Bit) Flags() BGFlags { return BGFlagsFromInt(bg.FlagsRaw) }
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// Copyright 2019 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package disklayout
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// BlockGroup64Bit emulates struct ext4_group_desc in fs/ext4/ext4.h.
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// It is the block group descriptor struct for 64-bit ext4 filesystems.
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// It implements BlockGroup interface. It is an extension of the 32-bit
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// version of BlockGroup.
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//
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// The suffix `Hi` here stands for upper bits because they represent the upper
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// half of the fields.
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type BlockGroup64Bit struct {
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// We embed the 32-bit struct here because 64-bit version is just an extension
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// of the 32-bit version.
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BlockGroup32Bit
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// 64-bit specific fields.
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BlockBitmapHi uint32
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InodeBitmapHi uint32
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InodeTableHi uint32
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FreeBlocksCountHi uint16
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FreeInodesCountHi uint16
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UsedDirsCountHi uint16
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ItableUnusedHi uint16
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ExcludeBitmapHi uint32
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BlockBitmapChecksumHi uint16
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InodeBitmapChecksumHi uint16
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_ uint32 // Padding to 64 bytes.
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}
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// Methods to override. Checksum() and Flags() are not overridden.
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// InodeTable implements BlockGroup.InodeTable.
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func (bg *BlockGroup64Bit) InodeTable() uint64 {
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return (uint64(bg.InodeTableHi) << 32) | uint64(bg.InodeTableLo)
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}
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// BlockBitmap implements BlockGroup.BlockBitmap.
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func (bg *BlockGroup64Bit) BlockBitmap() uint64 {
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return (uint64(bg.BlockBitmapHi) << 32) | uint64(bg.BlockBitmapLo)
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}
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// InodeBitmap implements BlockGroup.InodeBitmap.
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func (bg *BlockGroup64Bit) InodeBitmap() uint64 {
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return (uint64(bg.InodeBitmapHi) << 32) | uint64(bg.InodeBitmapLo)
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}
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// ExclusionBitmap implements BlockGroup.ExclusionBitmap.
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func (bg *BlockGroup64Bit) ExclusionBitmap() uint64 {
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return (uint64(bg.ExcludeBitmapHi) << 32) | uint64(bg.ExcludeBitmapLo)
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}
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// FreeBlocksCount implements BlockGroup.FreeBlocksCount.
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func (bg *BlockGroup64Bit) FreeBlocksCount() uint32 {
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return (uint32(bg.FreeBlocksCountHi) << 16) | uint32(bg.FreeBlocksCountLo)
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}
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// FreeInodesCount implements BlockGroup.FreeInodesCount.
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func (bg *BlockGroup64Bit) FreeInodesCount() uint32 {
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return (uint32(bg.FreeInodesCountHi) << 16) | uint32(bg.FreeInodesCountLo)
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}
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// DirectoryCount implements BlockGroup.DirectoryCount.
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func (bg *BlockGroup64Bit) DirectoryCount() uint32 {
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return (uint32(bg.UsedDirsCountHi) << 16) | uint32(bg.UsedDirsCountLo)
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}
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// UnusedInodeCount implements BlockGroup.UnusedInodeCount.
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func (bg *BlockGroup64Bit) UnusedInodeCount() uint32 {
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return (uint32(bg.ItableUnusedHi) << 16) | uint32(bg.ItableUnusedLo)
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}
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// BlockBitmapChecksum implements BlockGroup.BlockBitmapChecksum.
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func (bg *BlockGroup64Bit) BlockBitmapChecksum() uint32 {
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return (uint32(bg.BlockBitmapChecksumHi) << 16) | uint32(bg.BlockBitmapChecksumLo)
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}
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// InodeBitmapChecksum implements BlockGroup.InodeBitmapChecksum.
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func (bg *BlockGroup64Bit) InodeBitmapChecksum() uint32 {
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return (uint32(bg.InodeBitmapChecksumHi) << 16) | uint32(bg.InodeBitmapChecksumLo)
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}
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// Copyright 2019 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package disklayout
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import (
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"testing"
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"gvisor.dev/gvisor/pkg/binary"
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)
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// TestBlockGroupSize tests the fact that the block group struct for
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// 32-bit ext filesystems should be exactly 32 bytes big and for 64-bit fs it
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// should be 64 bytes.
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func TestBlockGroupSize(t *testing.T) {
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if got, want := int(binary.Size(BlockGroup32Bit{})), 32; got != want {
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t.Errorf("BlockGroup32Bit should be exactly 32 bytes but is %d bytes", got)
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}
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if got, want := int(binary.Size(BlockGroup64Bit{})), 64; got != want {
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t.Errorf("BlockGroup64Bit should be exactly 64 bytes but is %d bytes", got)
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}
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}
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