From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Xen-devel <xen-devel@lists.xen.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <Ian.Jackson@eu.citrix.com>,
Wei Liu <wei.liu2@citrix.com>
Subject: [PATCH v4 11/29] docs: Libxl migration v2 stream specification
Date: Tue, 14 Jul 2015 11:59:26 +0100 [thread overview]
Message-ID: <1436871584-6522-12-git-send-email-andrew.cooper3@citrix.com> (raw)
In-Reply-To: <1436871584-6522-1-git-send-email-andrew.cooper3@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
---
v3: Spelling fixes
---
docs/specs/libxl-migration-stream.pandoc | 205 ++++++++++++++++++++++++++++++
1 file changed, 205 insertions(+)
create mode 100644 docs/specs/libxl-migration-stream.pandoc
diff --git a/docs/specs/libxl-migration-stream.pandoc b/docs/specs/libxl-migration-stream.pandoc
new file mode 100644
index 0000000..4192950
--- /dev/null
+++ b/docs/specs/libxl-migration-stream.pandoc
@@ -0,0 +1,205 @@
+% LibXenLight Domain Image Format
+% Andrew Cooper <<andrew.cooper3@citrix.com>>
+% Draft B
+
+Introduction
+============
+
+For the purposes of this document, `xl` is used as a representation of any
+implementer of the `libxl` API. `xl` should be considered completely
+interchangeable with alternates, such as `libvirt` or `xenopsd-xl`.
+
+Purpose
+-------
+
+The _domain image format_ is the context of a running domain used for
+snapshots of a domain or for transferring domains between hosts during
+migration.
+
+There are a number of problems with the domain image format used in Xen 4.5
+and earlier (the _legacy format_)
+
+* There is no `libxl` context information. `xl` is required to send certain
+ pieces of `libxl` context itself.
+
+* The contents of the stream is passed directly through `libxl` to `libxc`.
+ The legacy `libxc` format contained some information which belonged at the
+ `libxl` level, resulting in awkward layer violation to return the
+ information back to `libxl`.
+
+* The legacy `libxc` format was inextensible, causing inextensibility in the
+ legacy `libxl` handling.
+
+This design addresses the above points, allowing for a completely
+self-contained, extensible stream with each layer responsible for its own
+appropriate information.
+
+
+Not Yet Included
+----------------
+
+The following features are not yet fully specified and will be
+included in a future draft.
+
+* Remus
+
+* ARM
+
+
+Overview
+========
+
+The image format consists of a _Header_, followed by 1 or more _Records_.
+Each record consists of a type and length field, followed by any type-specific
+data.
+
+\clearpage
+
+Header
+======
+
+The header identifies the stream as a `libxl` stream, including the version of
+this specification that it complies with.
+
+All fields in this header shall be in _big-endian_ byte order, regardless of
+the setting of the endianness bit.
+
+ 0 1 2 3 4 5 6 7 octet
+ +-------------------------------------------------+
+ | ident |
+ +-----------------------+-------------------------+
+ | version | options |
+ +-----------------------+-------------------------+
+
+--------------------------------------------------------------------
+Field Description
+----------- --------------------------------------------------------
+ident 0x4c6962786c466d74 ("LibxlFmt" in ASCII).
+
+version 0x00000002. The version of this specification.
+
+options bit 0: Endianness. 0 = little-endian, 1 = big-endian.
+
+ bit 1: Legacy Format. If set, this stream was created by
+ the legacy conversion tool.
+
+ bits 2-31: Reserved.
+--------------------------------------------------------------------
+
+The endianness shall be 0 (little-endian) for images generated on an
+i386, x86_64, or arm host.
+
+\clearpage
+
+
+Records
+=======
+
+A record has a record header, type specific data and a trailing footer. If
+`length` is not a multiple of 8, the body is padded with zeroes to align the
+end of the record on an 8 octet boundary.
+
+ 0 1 2 3 4 5 6 7 octet
+ +-----------------------+-------------------------+
+ | type | body_length |
+ +-----------+-----------+-------------------------+
+ | body... |
+ ...
+ | | padding (0 to 7 octets) |
+ +-----------+-------------------------------------+
+
+--------------------------------------------------------------------
+Field Description
+----------- -------------------------------------------------------
+type 0x00000000: END
+
+ 0x00000001: LIBXC_CONTEXT
+
+ 0x00000002: XENSTORE_DATA
+
+ 0x00000003: EMULATOR_CONTEXT
+
+ 0x00000004 - 0x7FFFFFFF: Reserved for future _mandatory_
+ records.
+
+ 0x80000000 - 0xFFFFFFFF: Reserved for future _optional_
+ records.
+
+body_length Length in octets of the record body.
+
+body Content of the record.
+
+padding 0 to 7 octets of zeros to pad the whole record to a multiple
+ of 8 octets.
+--------------------------------------------------------------------
+
+\clearpage
+
+END
+----
+
+A end record marks the end of the image, and shall be the final record
+in the stream.
+
+ 0 1 2 3 4 5 6 7 octet
+ +-------------------------------------------------+
+
+The end record contains no fields; its body_length is 0.
+
+LIBXC\_CONTEXT
+--------------
+
+A libxc context record is a marker, indicating that the stream should be
+handed to `xc_domain_restore()`. `libxc` shall be responsible for reading its
+own image format from the stream.
+
+ 0 1 2 3 4 5 6 7 octet
+ +-------------------------------------------------+
+
+The libxc context record contains no fields; its body_length is 0[^1].
+
+
+[^1]: The sending side cannot calculate ahead of time how much data `libxc`
+might write into the stream, especially for live migration where the quantity
+of data is partially proportional to the elapsed time.
+
+XENSTORE\_DATA
+-------------
+
+A record containing xenstore key/value pairs of data.
+
+ 0 1 2 3 4 5 6 7 octet
+ +-------------------------------------------------+
+ | xenstore key/value pairs |
+ ...
+ +-------------------------------------------------+
+
+EMULATOR\_CONTEXT
+----------------
+
+A context blob for a specific emulator associated with the domain.
+
+ 0 1 2 3 4 5 6 7 octet
+ +------------------------+------------------------+
+ | emulator_id | index |
+ +------------------------+------------------------+
+ | emulator_ctx |
+ ...
+ +-------------------------------------------------+
+
+--------------------------------------------------------------------
+Field Description
+------------ ---------------------------------------------------
+emulator_id 0x00000000: Unknown (In the case of a legacy stream)
+
+ 0x00000001: Qemu Traditional
+
+ 0x00000002: Qemu Upstream
+
+ 0x00000003 - 0xFFFFFFFF: Reserved for future emulators.
+
+index Index of this emulator for the domain, if multiple
+ emulators are in use.
+
+emulator_ctx Emulator context blob.
+--------------------------------------------------------------------
--
1.7.10.4
next prev parent reply other threads:[~2015-07-14 10:59 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-14 10:59 [PATCH v4 00/27] Libxl migration v2 Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 01/29] bsd-sys-queue-h-seddery: Massage `offsetof' Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 02/29] tools/libxc: Always compile the compat qemu variables into xc_sr_context Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 03/29] tools/libxl: Introduce ROUNDUP() Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 04/29] tools/libxl: Introduce libxl__kill() Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 05/29] tools/libxl: Stash all restore parameters in domain_create_state Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 06/29] tools/libxl: Split libxl__domain_create_state.restore_fd in two Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 07/29] tools/libxl: Extra management APIs for the save helper Andrew Cooper
2015-07-14 13:23 ` Ian Jackson
2015-07-14 10:59 ` [PATCH v4 08/29] tools/libxl: Add save_helper_state pointers to libxl__xc_domain_{save, restore}() Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 09/29] tools/libxl: Fix libxl__carefd_opened() to be more useful with an invalid fd Andrew Cooper
2015-07-14 13:39 ` Ian Jackson
2015-07-14 14:08 ` Ian Campbell
2015-07-14 10:59 ` [PATCH v4 10/29] tools/xl: Mandatory flag indicating the format of the migration stream Andrew Cooper
2015-07-14 10:59 ` Andrew Cooper [this message]
2015-07-14 10:59 ` [PATCH v4 12/29] tools/python: Libxc migration v2 infrastructure Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 13/29] tools/python: Libxl " Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 14/29] tools/python: Other migration infrastructure Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 15/29] tools/python: Verification utility for v2 stream spec compliance Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 16/29] tools/python: Conversion utility for legacy migration streams Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 17/29] tools/libxl: Migration v2 stream format Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 18/29] tools/libxl: Infrastructure for reading a libxl migration v2 stream Andrew Cooper
2015-07-14 13:32 ` Ian Jackson
2015-07-14 10:59 ` [PATCH v4 19/29] tools/libxl: Infrastructure to convert a legacy stream Andrew Cooper
2015-07-14 13:33 ` Ian Jackson
2015-07-14 10:59 ` [PATCH v4 20/29] tools/libxl: Convert a legacy stream if needed Andrew Cooper
2015-07-14 13:37 ` Ian Jackson
2015-07-14 10:59 ` [PATCH v4 21/29] tools/libxc+libxl+xl: Restore v2 streams Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 22/29] tools/libxl: Infrastructure for writing a v2 stream Andrew Cooper
2015-07-14 13:40 ` Ian Jackson
2015-07-14 10:59 ` [PATCH v4 23/29] tools/libxc+libxl+xl: Save v2 streams Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 24/29] docs/libxl: Introduce CHECKPOINT_END to support migration v2 remus streams Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 25/29] tools/libxl: Write checkpoint records into the stream Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 26/29] tools/libx{c, l}: Introduce restore_callbacks.checkpoint() Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 27/29] tools/libxl: Handle checkpoint records in a libxl migration v2 stream Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 28/29] tools/libxc: Drop all XG_LIBXL_HVM_COMPAT code from libxc Andrew Cooper
2015-07-14 10:59 ` [PATCH v4 29/29] tools/libxl: Drop all knowledge of toolstack callbacks Andrew Cooper
2015-07-15 10:21 ` [PATCH v4 00/27] Libxl migration v2 Wei Liu
2015-07-15 10:25 ` Ian Jackson
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