* Michael S. Tsirkin (m...@redhat.com) wrote: > On Tue, Mar 25, 2014 at 08:17:11PM +0000, Dr. David Alan Gilbert (git) wrote:
<snip> > > 5) At the moment you select BER output format by setting an environment > > variable ( export QEMUMIGFORMAT=BER ) , I need to put more thought > > in to the right way to do this, there are some harder questions like > > what happens to devices that are still using pre-vmstate encodings > > (that are currently sent as blobs) when they eventually convert over > > and thus how to keep compatibility with earlier BER output versions > > where they were blobs. > > A simple way is the way we always changed migration > format - trying this to the machine type. > Old machine type gets you binary, newer one BER with blobs, > then we can add more flags gradually. Right, that should work; it gets a little messy to tie machine type to formats for individual devices, but no big issue. > With BER we'll actually be able to do smarter things in the future, > such as send out multiple formats and have destination select > the one it understands, but this isn't mandatory as a first step. > > > 6) At the moment for blobs (i.e. pre-vmstate) the whole blob gets loaded > > into memory and then processed; that's not necessary and can be done > > with a QEMUFile shim. > > 7) I need to sort out my Error** handling (probably in a lot of places) > > That's mostly broken in migration as it is. > > > 8) The visitors should be able to share much more code. > > > > The not-yet-done: > > a) XBZRLE > > b) block-migration > > c) SPAPR (it's an iterative migration like RAM and block) > > d) RDMA (I'm guessing I've broken it, but haven't tried) > > e) Floats are currently sent as blobs. > > So at least a,b and c need to be done. Yep, agreed; iterative migration stuff has direct byte/word putting all over so is rather manual, so I just did enough to get it going first. > Not sure about RDMA - it was never supported and no one > seems to work on it. > Maybe, somehow, it can use the old format when enabled? I think Michael still throws bug fixes in from time to time, however my worry is actually more about the Visitor conversion than the actual format change that might break it; anyway needs testing and then we'll see. > > What I've done: > > There are separate output visitors (binary compatible, debug and BER) and > > they're selected by setting QEMUMIGFORMAT to one of 'debug', 'BER' or just > > leaving it unset. > > > > The Input visitor is selected automatically from the first 4 bytes of the > > file. > > Not really necessary if you use machine type. It's easy anyway. > > In general most types are BER sequences of indefinite length, with some > > types that I've allocated an Application specific type tag to. There is a > > hook > > to give any VMState it's own type tag (which I've shown using one example > > for cpu-common). Integers and strings are standard 'universal' types. > > > > Objects with .get/.put methods or register_savevm are saved as an 'octet > > string'. > > There are a few places where a device registered with .get/.put calls back > > into > > vmstate_save_state for part of their state (typically for devices built on > > PCI) > > and when they do that, even when in BER mode, those components get stored > > inside > > the octet string in the old format. > > > > I've used the 'asn1c' tool to validate the schema (which is > > in docs/specs/migration.schema) and also to verify streams that I've > > produced > > match the schema. > > > > I've tested it with virt-test (hacked to have different source/dest > > qemu's) > > and tried bin-bin, ber-ber, and pre-visitor-qemu -> this and > > this -> pre-visitor-qemu just on the standard migration.default.tcp > > migration > > test, but I've not tried a large combination of configurations. > > > > My fix for qemu_peek_buffer that's on the list is needed to stabilise > > the binary format input visitor. > > > > I'll keep chipping away at that list, and would expect to pop another > > version out in a month or so. > > > > Dave > > > > Dr. David Alan Gilbert (16): > > Visitor: Add methods for migration format use > > QEMUSizedBuffer/QEMUFile > > qemu-file: Add set/get tmp_visitor > > Header/constant/types fixes for visitors > > Visitor: Binary compatible output visitor > > Visitor: Debug output visitor > > Visitor: Binary compatible input visitor > > Visitor: Output path > > Visitor: Load path > > Visitor: Common types to use visitors > > Choose output visitor based on env variable > > BER Visitor: Create output visitor > > BER Visitor: Create input visitor > > Start some BER format docs > > ASN.1 schema for new migration format > > Wire in BER visitors > > One nifty feature of Stefan's patches was that a > set of unit tests for parser was included. > Worth reusing? Yes, unit tests are one thing I missed off my list but know need doing. Dave -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
