Re: [Qemu-devel] [PATCH 4/5] milkymist-softusb: Don't map RAM memory regions in the device itself

[Paolo Bonzini]

Il 15/02/2013 16:35, Peter Maydell ha scritto:
>> > I think it's best to avoid storing long-lived host pointers.  Ideally we
>> > should have no long-lived host pointers anytime the thread is quiescent
>> > (for CPUs that means kvm_cpu_exec or the end of qemu_tcg_wait_io_event;
>> > for I/O that means select/poll).
>> >
>> > Can you call memory_region_get_ram_ptr from the read/write functions?
> I could, but does it buy us anything in particular? (alternatively,
> what's the reason why we should avoid storing the host pointers?
> We do it in a number of other devices...)

I find it more complex to reason about finer-grained locking
(particularly regarding the lifetimes) when you have object A storing
something into object B.  In practice it should be handled just fine by
reference counting, but I still find it harder to wrap my head around it.

Paolo