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PXAR Format

Background

We are currently building a go library for the PXAR Archive format, and have been gathering information about the format by dissecting the archives and gathering information from the proxmox repository and other tools (mainly @tizbac s proxmoxbackupclient_go)

Official Overview (V1 format)

alt text

Base Entry Types

Name Identifier Description
PXAR_ENTRY 0xd5956474e588acef Stores metadata information about the entry
PXAR_ENTRY_V1 0x11da850a1c1cceff Older version of PXAR_ENTRY
PXAR_FILENAME 0x16701121063917b3 Stores the filename of the following item
PXAR_PAYLOAD 0x28147a1b0b7c1a25 The entry payload, e.g. symlink target or file contents
PXAR_SYMLINK 0x27f971e7dbf5dc5f Stores symlink target and metadata
PXAR_HARDLINK 0x51269c8422bd7275 Stores hardlink
PXAR_GOODBYE 0x2fec4fa642d5731d PXAR_GOODBYE contains hashes of all files in a folder
PXAR_GOODBYE_TAIL_MARKER 0xef5eed5b753e1555 End of goodbye record
PXAR_DEVICE 0x9fc9e906586d5ce9 Stores information about device records
PXAR_XATTR 0x0dab0229b57dcd03 Stores extended attributes for a file/folder
PXAR_ACL_USER 0x2ce8540a457d55b8 User ACL Entries
PXAR_ACL_GROUP 0x136e3eceb04c03ab Group ACL Entries
PXAR_ACL_GROUP_OBJ 0x10868031e9582876 ACL_GROUP_OBJ
PXAR_ACL_DEFAULT 0xbbbb13415a6896f5 various default ACL fields
PXAR_ACL_DEFAULT_USER 0xc89357b40532cd1f User ACL Entries
PXAR_ACL_DEFAULT_GROUP 0xf90a8a5816038ffe Group ACL Entries
PXAR_FCAPS 0x2da9dd9db5f7fb67 File capability information, Linux disk format
PXAR_QUOTA_PROJID 0xe07540e82f7d1cbb Quota information

Order

File

  • PXAR_ENTRY
  • PXAR_FILENAME
  • PXAR_XATTR
  • PXAR_ACL
  • PXAR_FCAPS
  • PXAR_QUOTA_PROJID
  • PXAR_PAYLOAD

Folder

  • PXAR_ENTRY
  • PXAR_FILENAME
    • Files, links, nested folders
  • PXAR_GOODBYE

Common

  • All records include a descriptor header (table below)
  • All numbers are little-endian
Field Type Description Example
Type uint64 The identifier from the table above 0xd5956474e588acef
Length uint64 The length of the following record + 16 (length of self) 56

PXAR_ENTRY

Length: Fixed, linux stat struct length as uint64

Field Type Description Example
Mode uint64 File or folder mode 0o777
Flags uint64 Flags on the object 0
Uid uint32 User ID 1000
Gid uint32 Group ID 1000
MtimeSecs uint64 ModifiedTime Seconds 0
MtimeNanos uint32 ModifiedTime Nanoseconds 0
MtimePadding uint32 ModifiedTime Padding 0

PXAR_FILENAME

Length: Variable, max length 4096 + 1 (null-termination)

Field Type Description Example
Filename []byte The decoded filename test.txt
Null Termination byte Terminates the filename with a null byte 0x00

PXAR_PAYLOAD

Length: Variable, max length MAX(uint64) - size of headers

Field Type Description Example
Content []byte The decoded filename hello world

PXAR_SYMLINK, PXAR_HARDLINK

Length: Variable, max length 4096

Field Type Description Example
Content []byte The symlink target /etc/target

PXAR_GOODBYE, PXAR_GOODBYE_TAIL

Length: Variable, max length MAX(uint64) - size of headers. 24*len(PXAR_GOODBYE)

Field Type Description Example
Hash uint64 The filename hash for a given file. The last record in an archive (PXAR_GOODBYE_TAIL) always has the hash value 0xef5eed5b753e1555 0xabcdef1234567890
Offset uint64 The offset where the referenced item starts 10
Len uint64 The length of the referenced item 100