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Savegames: Difference between revisions

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This page describes the format of save files contained in NAND. These files are stored as completely unencrypted, plaintext data. Save files are not cleared upon creation, resulting in possible garbage data in unused portions of the container.
This page describes the format of save files contained in NAND. These files are stored as completely unencrypted, plaintext data. Save files are not cleared upon creation, resulting in possible garbage data in unused portions of the container.


== Main header ==
= Main header =


The header is 0x4000 bytes long.
The header is 0x4000 bytes long.


There are 2 headers stored at 0x0 and 0x4000, presumably for commit and rollback purposes.
There are 2 headers stored at 0x0 and 0x4000, presumably for commit and rollback purposes.
Decimal versions are separated as Major, Minor, Micro, and Bugfix with each using one byte. e.g. version 3.4.5.6 would be 0x03040506.


{| class="wikitable"
{| class="wikitable"
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The additional storage at the end of the header is used to store any extra header data. This data's structure is determined by offsets stored in the main part of the header.
The additional storage at the end of the header is used to store any extra header data. This data's structure is determined by offsets stored in the main part of the header.


=== AES CMAC header ===
== AES CMAC header ==
 
This is internally referred to as MasterHeaderMac.
 
{| class="wikitable"
{| class="wikitable"
|-
|-
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The final CMAC key used for this is generated using GenerateAesKek with a kek source and the device key, along with and LoadAesKey and a set key seed.
The final CMAC key used for this is generated using GenerateAesKek with a kek source and the device key, along with and LoadAesKey and a set key seed.


=== DISF ===
== DISF ==


This section contains information about the structure of the save file.
This section contains information about the structure of the save file.
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| 0x004
| 0x004
| 4
| 4
| Version (Upper 2 bytes must be 0x0004)
| Version (Major version must be 4 or 5. Only system version 5.0.0+ can read version 5 save files)
|-
|-
| 0x008
| 0x008
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|}
|}


=== Integrity verification header ===
== Integrity verification header ==


* Offsets for levels 1-3 come from the metadata remap storage
* Offsets for levels 1-3 come from the metadata remap storage
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| 0x04
| 0x04
| 4
| 4
| Version (Upper 2 bytes must be 0x0002)
| Version (0.2.x.x)
|-
|-
| 0x08
| 0x08
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|}
|}


==== Level information ====
=== Level information ===


* 0x18 bytes long
* 0x18 bytes long
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|}
|}


=== Journal header ===
== Journal header ==


{| class="wikitable"
{| class="wikitable"
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| 0x04
| 0x04
| 4
| 4
| Version (Must be 0x10000 or less)
| Version (Must be 0.0.x.x or 0.1.0.0)
|-
|-
| 0x08
| 0x08
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|}
|}


==== Journal map header ====
=== Journal map header ===


{| class="wikitable"
{| class="wikitable"
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| 0x00
| 0x00
| 4
| 4
| Version (Must be 0 or 1)
| Version (Stored as a normal 32-bit integer. Must be 0 or 1)
|-
|-
| 0x04
| 0x04
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|}
|}


=== Extra data ===
== Extra data ==


{| class="wikitable"
{| class="wikitable"
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| 0x00
| 0x00
| 0x40
| 0x40
| [[Filesystem_services#Save_Struct|Save Struct]]
| [[Filesystem_services#SaveDataAttribute|SaveDataAttribute]]
|-
|-
| 0x40
| 0x40
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|}
|}


== Remap Storage ==
= Remap Storage =


Remap Storage is used to remap segments of data from virtual offsets to physical offsets. This allows extending the save file without having to relocate existing data.
Remap Storage is used to remap segments of data from virtual offsets to physical offsets. This allows extending the save file without having to relocate existing data.
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Segment index: 0x3 Offset: 0x000000000000100
Segment index: 0x3 Offset: 0x000000000000100


=== Remap storage header ===
== Remap storage header ==


{| class="wikitable"
{| class="wikitable"
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| 0x04
| 0x04
| 4
| 4
| Version (Must be 0x10000 or less)
| Version (Must be 0.0.x.x or 0.1.x.x)
|-
|-
| 0x08
| 0x08
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|}
|}


=== Remapping Entry ===
== Remapping Entry ==


{| class="wikitable"
{| class="wikitable"
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|}
|}


== Duplex Storage ==
= Duplex Storage =


A Duplex Storage contains four separate elements: [[#Duplex header|a header]], a bitmap, and two identically-sized chunks of data.
A Duplex Storage contains four separate elements: [[#Duplex header|a header]], a bitmap, and two identically-sized chunks of data.
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As hinted by the name, a Duplex Storage contains two main chunks of data. To store X bytes, two chunks of data each with size X are required.
As hinted by the name, a Duplex Storage contains two main chunks of data. To store X bytes, two chunks of data each with size X are required.


=== Bitmap ===
== Bitmap ==


This main data storage is split into blocks of the size indicated in the duplex header. The bitmap contains as many bits as the main data has blocks. If the main data is 0x40000 bytes long with a block size of 0x4000 bytes, the bitmap would contain 0x10 bits.
This main data storage is split into blocks of the size indicated in the duplex header. The bitmap contains as many bits as the main data has blocks. If the main data is 0x40000 bytes long with a block size of 0x4000 bytes, the bitmap would contain 0x10 bits.
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The bitmap controls which data chunk is active for each block. e.g. If bit 3 of the bitmap is a 0 then block 3 of data chunk 0 is active and block 3 of data chunk 1 is inactive. This means that when data from block 3 is read, the data from chunk 0 will be returned and the data from chunk 1 will be completely ignored.
The bitmap controls which data chunk is active for each block. e.g. If bit 3 of the bitmap is a 0 then block 3 of data chunk 0 is active and block 3 of data chunk 1 is inactive. This means that when data from block 3 is read, the data from chunk 0 will be returned and the data from chunk 1 will be completely ignored.


=== Hierarchical Duplex Storage ===
== Hierarchical Duplex Storage ==


Multiple Duplex Storages can be chained together to gain various benefits. With a Hierarchical Duplex Storage, the bitmap for the main data is stored inside another Duplex Storage.
Multiple Duplex Storages can be chained together to gain various benefits. With a Hierarchical Duplex Storage, the bitmap for the main data is stored inside another Duplex Storage.
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This allows for atomic operations on the Hierarchical Duplex Storage. When writing to the storage, data will be written to the inactive blocks and inactive bitmaps. When the data is committed the bit in the save file header is flipped, changing which master bitmap is active.
This allows for atomic operations on the Hierarchical Duplex Storage. When writing to the storage, data will be written to the inactive blocks and inactive bitmaps. When the data is committed the bit in the save file header is flipped, changing which master bitmap is active.


=== Duplex header ===
== Duplex header ==


* Block sizes are stored as powers of 2
* Block sizes are stored as powers of 2
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| 0x04
| 0x04
| 4
| 4
| Version (Upper 2 bytes must be 0x0001)
| Version (0.1.x.x)
|-
|-
| 0x08
| 0x08
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|}
|}


== Save FS ==
= Save FS =


=== Save FS header ===
== Save FS header ==


* Structure is different than 3DS.
* Structure is different than 3DS.
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| 0x04
| 0x04
| 4
| 4
| Version (Upper 2 bytes must be 0x0006)
| Version (0.6.x.x)
|-
|-
| 0x08
| 0x08
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|-
|-
|}
|}
== File allocation table ==
The savedata FS uses an allocation table to keep track of block allocation. This FAT contains doubly-linked lists of the blocks allocated to each file. Each entry in the FAT is 8 bytes in size.
FAT entry 0 is reserved for the list of free blocks. Because of this, the FAT entry for block n is found at FAT index n+1. The indexes stored in FAT entries refer the index of the next/previous FAT entry in the chain, not the index of the next/previous block.
The FAT header is internally called AllocationTableControlArea. The FAT itself is called AllocationTableMeta. The actual save FS data is called AllocationTableData.


=== File allocation table header ===
=== File allocation table header ===
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|}
|}


=== Directory Table Entry ===
=== File allocation table entry ===
 
{| class="wikitable"
|-
! Start
! Length
! Description
|-
| 0
| 4 (High bit)
| Set if entry is the first entry in the list.
|-
| 0
| 4 (Lower 31 bits)
| Previous entry index. First entry in list if 0.
|-
| 4
| 4 (High bit)
| Set if the allocation segment has multiple blocks.
|-
| 4
| 4 (Lower 31 bits)
| Next entry index. Last entry in list if 0.
|-
|}


* Index 0 is the start of a linked list that contains all invalid/inactive directories.
If the allocation segment has multiple blocks, the first entry will be followed by a range descriptor entry. The last entry in the segment will contain a duplicate of this entry.
* Index 1 is the start of a linked list that contains all valid/active directories.
 
* Index 2 is the root directory.
{| class="wikitable"
|-
! Start
! Length
! Description
|-
| 0
| 4 (High bit)
| Always set.
|-
| 0
| 4 (Lower 31 bits)
| First entry in this segment.
|-
| 4
| 4 (High bit)
| Never set.
|-
| 4
| 4 (Lower 31 bits)
| Last entry in this segment.
|-
|}
 
== Save File Table ==
 
The save file table is similar to the RomFS file table, except the save file table uses linked lists instead of dictionaries.
 
The table contains a list of directory entries and a list of file entries. Their respective types are:<br />
'''SaveFsList<SaveFileTableEntry<SaveDirectoryInfo>>'''<br />
'''SaveFsList<SaveFileTableEntry<SaveFileInfo>>'''
 
=== Save File Table Entry ===
 
SaveFileTableEntry<class T>


{| class="wikitable"
{| class="wikitable"
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| 0x00
| 0x00
| 4
| 4
| Parent directory node index
| Next entry index. A value of 0 indicates the end of the list.
|-
|-
| 0x04
| 0x04
| 64
| sizeof(T)
| Filename
| Value of type T.
|-
|-
| 0x44
|}
| 4
 
| Next sibling directory node index
=== Save File Info ===
 
Holds the information of a single file.
 
{| class="wikitable"
|-
! Start
! Length
! Description
|-
|-
| 0x48
| 0x00
| 4
| 4
| First child directory node index
| Starting block index.
|-
|-
| 0x4c
| 0x04
| 8
| 8
| First child file node index
| File length in bytes.
|-
|-
| 0x54
| 0x0C
| 8
| 8
| Unused?
| Reserved.
|-
|}
 
=== Save Directory Info ===
 
Holds the information of a single directory.
 
{| class="wikitable"
|-
! Start
! Length
! Description
|-
| 0x00
| 4
| First child directory index. 0 if none.
|-
|-
| 0x5c
| 0x04
| 4
| 4
| Next directory node index in the chain of invalid or valid directories. If this is the first block in a list of length 0, this value will contain the total number of directory nodes.
| First child file index. 0 if none.
|-
| 0x08
| 0xC
| Reserved.
|-
|-
|}
|}


=== File Table Entry ===
== Save FS List ==
 
SaveFsList<class T>
 
This is a linked list that is used internally by '''Save File Table''' as a key-value store. Integer/string pairs are used as keys. The list is represented as a single array so that it can be easily stored and read from a file. Entry indexes 0 and 1 are reserved.
 
Index 0 is the start of a list containing all free entries. When an item in the list is removed, the entry it was using is added to this list for future reuse.
 
Index 1 is the start of a list containing all currently used entries.


* Index 0 is the start of a linked list that contains all invalid/inactive files.
The first 8 bytes of the list are used as follows. Indexes 0 and 1 are included in these counts.
* Index 1 is the start of a linked list that contains all valid/active files.


{| class="wikitable"
{| class="wikitable"
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| 0x00
| 0x00
| 4
| 4
| Parent directory node index
| The size of the list. Freed entries that have not been reused are included in the count.
|-
|-
| 0x04
| 0x04
| 64
| 4
| Filename
| The current capacity of the list based on the number of bytes allocated.
|-
|-
| 0x44
|}
 
=== Save FS List Key ===
 
{| class="wikitable"
|-
! Start
! Length
! Description
|-
| 0x00
| 4
| 4
| Next sibling file node index
| 32-bit integer.
|-
| 0x04
| 0x40
| 0x40-byte string.
|-
|-
| 0x48
|}
| 4
 
| Index of the block that the file starts at
=== Save FS List Entry ===
 
{| class="wikitable"
|-
! Start
! Length
! Description
|-
|-
| 0x4c
| 0x00
| 8
| 0x44
| File size in bytes
| Key.
|-
|-
| 0x54
| 0x44
| 8
| sizeof(T)
| Unused?
| Value.
|-
|-
| 0x5c
| 0x44 + sizeof(T)
| 4
| 4
| Next file node index in the chain of invalid or valid files. If this is the first block in a list of length 0, this value will contain the total number of file nodes.
| Next entry node index. A value of 0 indicates the end of the list.
|-
|-
|}
|}
Retrieved from "https://switchbrew.org/wiki/Savegames"