On Tue, Sep 23, 2014 at 11:12:52AM -0600, Eric Blake wrote: > On 09/23/2014 04:09 AM, Stefan Hajnoczi wrote: > > +Rules support the following attributes: > > + > > + event - which type of operation to match (e.g. read_aio, write_aio, > > + flush_to_os, flush_to_disk). See the "Events" section for > > + information on events. > > TAB vs space damage?
Yes, thanks for spotting it. Fixed in v3. > > +Events > > +------ > > +Block drivers provide information about the type of I/O request they are > > about > > +to make so rules can match specific types of requests. For example, the > > qcow2 > > +block driver tells blkdebug when it accesses the L1 table so rules can > > match > > +only L1 table accesses and not other metadata or guest data requests. > > + > > +The core events are: > > + > > + read_aio - guest data read > > + > > + write_aio - guest data write > > + > > + flush_to_os - write out unwritten block driver state (e.g. cached > > metadata) > > + > > + flush_to_disk - flush the host block device's disk cache > > + > > +See block/blkdebug.c:event_names[] for the list of available events. You > > may > > s/available events/additional available events/ ? I'll say "for the full list of events" since event_names[] includes everything. > > +State transitions > > +----------------- > > +There are cases where more power is needed to match a particular I/O > > request in > > +a longer sequence of requests. For example: > > + > > + write_aio > > + flush_to_disk > > + write_aio > > + > > +How do we match the 2nd write_aio but not the first? This is where state > > +transitions come in. > > + > > +The error injection engine has an integer called the "state" that always > > starts > > +initialized to 1. Rules can be conditional on the state and they can > > +transition to a new state. > > Is the current state of the engine in a running guest introspectible, > such as through 'query-block'? No. > > + > > +For example, to match the 2nd write_aio: > > + > > + [set-state] > > + event = "write_aio" > > + state = "1" > > + new_state = "2" > > + > > + [inject-error] > > + event = "write_aio" > > + state = "2" > > + errno = "5" > > + > > +The first write_aio request matches the set-state rule and transitions from > > +state 0 to state 1. Once state 1 has been entered, the set-state rule no > > +longer matches since it required state 0. But the inject-error rule now > > state 0/1 or state 1/2 ? Thanks for catching this, I should explain the difference between state 0 and 1. This was a mistake because I original used "0" but it actually has to be "1".
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