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swift/etc/magic
Tim Burke ae062f8b09 ring: Introduce a v2 ring format
There's a bunch of moving pieces here:

- Add a new RingWriter class.

  Stick it in a new swift.common.ring.io module. You *can* use it like
  the old gzip file, but you can also define named sections which can
  be referenced later on read. Section names may be arbitrary strings,
  but the "swift/" prefix is reserved for upstream use. Sections must
  contain a single length-value encoded BLOB. If sections are used, an
  additional BLOB is written at the end containing a JSON section-index,
  followed by an uncompressed offset for the index.

  Move RingReader to ring/io.py, too.

- Clean up some ring metadata handling:

  - Drop MD5 tracking in RingReader. It was brittle at best anyway, and
    nothing uses it. YAGNI

  - Fix size/raw_size attributes when loading only metadata.

- Add the ability to seek within RingReaders, though you need to know
  what you're doing and only seek to flush points.

- Let RingBuilder objects change how wide their replica2part2dev_id
  arrays are. Add a dev_id_bytes key to serialized ring metadata.

  dev_id_bytes may be either 2 or 4, but 4 requires v2 rings. We
  considered allowing dev_id_bytes of 1, but dropped it as unnecessary
  complexity for a niche use case.

- swift-ring-builder version subcommand added, which takes a ring. This
  lets operators see the serialization format of a ring on disk:

  $ swift-ring-builder object.ring.gz version
  object.ring.gz: Serialization version: 2 (2-byte IDs), build version: 54

Signed-off-by: Tim Burke <tim.burke@gmail.com>
Change-Id: Ia0ac4ea2006d8965d7fdb6659d355c77386adb70
2025-07-21 11:37:15 -07:00

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#-------------------------------------------------------------------------------
# Openstack swift
# Note: add this snippet to either /etc/magic or ~/.magic
#-------------------------------------------------------------------------------
# gzip compressed
0 beshort 0x1f8b
# compress method: deflate, flags: FNAME
>&0 beshort 0x0808
# skip ahead another 6 (MTIME, XLF, OS); read FNAME
>>&6 search/0x40 \0
# Skip ahead five; should cover
# 00 -- uncompressed block
# 06 00 -- ... of length 6
# f9 ff -- (one's complement of length)
>>>&5 string/4 R1NG Swift ring,
>>>>&0 clear x
>>>>&0 beshort 1 version 1
>>>>&0 beshort 2 version 2
>>>>&0 default x
>>>>>&0 beshort x unknown version (0x%04x)