Hi,
I've been looking at reviving the migration-as-ber work that Michael and
Stefan looked at a while ago, and have stuff starting to work, but not
ready yet, so I thought I'd start by posting my current view
of an ASN.1 schema.
Note this is my 1st attempt at ASN.1 so feel free to pick holes!
This schema successfully passes asn1c and libtasn1's asn1Parser.
I've currently got a visitor modified Qemu that generated apparently
valid BER output (and compatible old-format) - unber and openssl asn1parse
dump it apparently happily, but I've not been able to find a tool to verify
it against the schema - suggestions welcome.
(* libtasn1's asn1Decoder OOMs my laptop/and or spits out a DER error, not
that I'm trying to encode as DER)
Some notes:
* I'm using the universal type codes for most things except the larger
scale structures/sequences where I've given them our own types.
* ASN type codes are disgustingly decimal, and even more disgustingly encoded
in BER, so having things readable in a hex dump is difficult; although the
values I've used end up with the last byte as an appropriate ASCII letter
and the other bytes would be if the top bit wasn't set.
* The 'shape' of it corresponds pretty closely to the shape of the existing
migration format; although I intend to clean it up a bit
- RAMSecEntry has the same flags that currently go into our binary format
but those can become more of an enum, and sima).
- I think SecFull/SecMin can probably merge together.
* Most things are just sequences, including most of VMState; I don't really
want to go around every VMState structure in the whole of QEMU allocating
a type ID, however I'm thinking about making it an optional VMState field
which I'd use if it was set.
* The only thing that worries me in terms of efficiency so far is the
'page is all 0' compression encoding which is rather verbose, for everything
else it seems that although it's chatty it's not that much of an overhead.
* I've not looked at block migration or spapr yet, (the only other iterative
migrate users)
* anything with a .get/.put or using the old style migration registration
gets bundled up into a blob as an octet-string - this means I don't have
to fix everything before it can start working.
As soon as I get the corresponding BER input visitor working and sweep the
sawdust out of my code I'll post it; probably a week or two.
Thoughts welcome,
Dave
--------------------------------------------------------------------------------
Qemu {}
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- Some basic types used in multiple places --
QemuString ::= UTF8String (SIZE (1..255))
-- TODO: 4096 is actually page size whatever that is
FullPage ::= OCTET STRING (SIZE (4096))
RAMBlockID ::= SEQUENCE {
name QemuString,
len INTEGER
}
RAMSecEntry ::= [ APPLICATION 8914 ] SEQUENCE {
addr INTEGER, -- Address or offset or size
flags INTEGER, -- maybe more explicit type?
name QemuString OPTIONAL,
body CHOICE {
bl SEQUENCE OF RAMBlockID,
compr INTEGER (0..255), -- Page filled with this value
page FullPage
-- TODO xbzrle --
}
}
RAMSecList ::= [ APPLICATION 9810 ] SEQUENCE OF RAMSecEntry
SubSection ::= [ APPLICATION 10707 ] SEQUENCE {
name QemuString,
versionid INTEGER,
contents SEQUENCE OF VMStateEntries
}
SubSecList ::= [ APPLICATION 10700 ] SEQUENCE OF SubSection
VMStateEntries ::= CHOICE {
-- Hmm need to think more --
dummy INTEGER,
subsecl SubSecList,
oldblob OCTET STRING
}
VMState ::= SEQUENCE OF VMStateEntries
-- Restrict to unsigned?
SectionID ::= INTEGER
SecFull ::= [ APPLICATION 2003 ] SEQUENCE {
name QemuString,
sectionid SectionID,
instanceid INTEGER,
versionid INTEGER,
contents CHOICE {
ramsec RAMSecList,
-- TODO other iterator initial stuff --
vmstate VMState
}
}
SecMin ::= [ APPLICATION 211 ] SEQUENCE {
sectionid SectionID,
contents CHOICE {
ramsec SEQUENCE OF RAMSecEntry
-- TODO other iterator general/end stuff --
}
}
Sections ::= CHOICE {
full SecFull,
min SecMin
}
-- The whole file --
-- Application tag used to get first 32bits of file
-- to come out as 7f cd c5 51 - the 51 is Q
-- the c5 and cd being E,M but with the top bit set
-- which BER requires
QemuFile ::= [ APPLICATION 1270481 ] SEQUENCE {
version INTEGER (3),
top SEQUENCE OF Sections
}
END
--------------------------------------------------------------------------------
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
