On 05/19/2015 08:06 AM, Dr. David Alan Gilbert wrote: >> Does it let us detect a corrupted >> stream earlier in the process? Or is the main benefit that it gives >> better error messages at the point corruption is first detected? > > Both; there are two cases that often happen; both triggered by a section > reading too little or too much, and it gets back to the main loop and > we read the next byte: > 1) the next byte on the stream is a 0x00 - that's read as an > end-of-migration > marker, we start the VM and you get a hung VM with no errors. > > 2) the next byte is between 0x01..0x04 - and it looks like a section > header, > then we try and read the next few bytes to figure out which section; > this could a) result in an error saying it's an unknown section or > b) Happen to match a section ID and then get an error about a problem > in that section. In either case you don't get an error pointing to > the previous section which was the actual problem.
Probably worth incorporating into the commit body then :) > >>> >>> The footers are tied to new machine types (on both pc types). >> >> Good that you tied it to machine type, but is it enough? When we added >> the optional section for giving the json representation of the stream, >> we ended up having to add a knob to turn off that section, so that >> backwards migration from a new qemu to an older one did not send it. >> I'm wondering if we'll need to expose a knob to turn off footers, again >> for the sake of backwards migration in downstream distros. > > That knob is already the knob that I've created and tied to the machine > type; the downstream distros will just turn the same knob in their old > machine types. I'm not asking about the machine type defaults, but a command line override: -machine suppress-vmdesc=on, commit 9850c604 [uggh - why'd we give that option an inverted name? Just so we could have a default of off? It might have been nicer as -machine send-vmdesc=off with a default of on for new machine types] -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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