Igor Mammedov <imamm...@redhat.com> writes:
> On Wed, 27 Nov 2013 15:35:09 +0100
> Markus Armbruster <arm...@redhat.com> wrote:
>
>> Igor Mammedov <imamm...@redhat.com> writes:
>>
>> > On Tue, 26 Nov 2013 15:49:05 +0100
>> > Markus Armbruster <arm...@redhat.com> wrote:
>> >
>> >> Igor Mammedov <imamm...@redhat.com> writes:
>> >>
>> >> > On Thu, 21 Nov 2013 11:12:43 +0100
>> >> > Markus Armbruster <arm...@redhat.com> wrote:
>> >> >
>> >> >> Igor Mammedov <imamm...@redhat.com> writes:
>> >> >>
>> > [...]
>> >> Two separate issues here:
>> >>
>> >> 1. The "no qemu_mem_opts have been specified" case
>> >>
>> >> This is equivalent to "empty options". Therefore, the case can be
>> >> eliminated by pre-creating empty options. No objection.
>> >>
>> >> The three existing merge_lists users don't do that. Perhaps they
>> >> should.
>> >>
>> >> 2. How to provide default values
>> >>
>> >> Supplying defaults is left to the caller of qemu_opt_get_FOO() by
>> >> design.
>> >>
>> >> Pre-creating option parameters deviates from that pattern. You
>> >> justify it by saying it "eliminates need to pepper code with
>> >> DEFAULT_RAM_SIZE * 1024 * 1024". How many occurrences?
>> > beside of vl.c for:
>> > mem & maxmem 1 in hw/i386/pc.c
>> > slots - 6 in several files
>>
>> Could the common code be factored out the old-fashioned way?
> replacing one one-liner with another might help a little but
> won't change a thing in general. It will be essentially the same.
Need to review your latest to have an opinion here :)
>> Precedence: qemu_get_machine_opts() encapsulates some QemuOpts-related
>> details, so its many users don't have to deal with them.
>>
>> > see below for continuation:
>> >
>> >>
>> >> Drawback: you lose the ability to see whether the user gave a value.
>> >> See below.
>> >>
>> > [...]
>> >> >> Ugly.
>> >> >>
>> >> >> Why is the variable called 'end'?
>> >> > would be 'suffix' better?
>> >>
>> >> end points to the whole value string, not the end of anything, and
>> >> neither to a suffix of anything.
>> > Any suggestions?
>>
>> What about val?
> I've replaced it with "mem_str" see
> "[PATCH 04/28] vl: convert -m to QemuOpts"
Works for me.
>> > [...]
>> >> >> If you refrain from putting defaults into opts, you can distinguish the
>> >> >> cases "user didn't specify maxmem, so assume mem", and "user specified
>> >> >> maxmem, so check it's >= mem".
>> >> > So foar, there is no point in distinguishing above cases,
>> >> > since maxmem <= mem is invalid value and hotplug should be disabled.
>> >> > So setting default maxmem to mem or anything less effectively
>> >> > disables hotplug.
>> >>
>> >> Yes, setting maxmem < mem is invalid and should be rejected, but not
>> >> setting maxmem at all should be accepted even when you set mem.
>> >>
>> >> Your patch like this pseudo-code:
>> >>
>> >> mem = DEFAULT_RAM_SIZE * 1024 * 1024
>> >> maxmem = mem
>> >>
>> >> if user specifies mem:
>> >> mem = user's mem
>> >> if user specifes max-mem:
>> >> mem = user's max-mem
>> >>
>> >> if max-mem < mem
>> >> what now?
>> >> should error our if max-mem and mem were specified by the user
>> >> shouldn't if user didn't specify max-mem!
>> >> but can't say whether he did
>> >>
>> >> I'd do it this way:
>> >>
>> >> mem = unset
>> >> maxmem = unset
>> >>
>> >> if user specifies mem:
>> >> mem = user's mem
>> >> if user specifes max-mem:
>> >> mem = user's max-mem
>> >>
>> >> if mem != unset && max-mem != unset && max-mem < mem
>> >> error
>> >>
>> >> I'd use QemuOpts for the user's command line, and no more. For anything
>> >> beyond that, I'd use ordinary variables, such as ram_size.
>> > Ok, I'll revert to the old code where options users check for option
>> > availability, it's not that much code.
>> >
>> >
>> > As for using QemuOpts as global store for global variables:
>> >
>> > * using local variables would require changing of machine init or/and
>> > QEMUMachine and changing functions signature pass them down the stack to
>> > consumers.
>>
>> Extending QEMUMachineInitArgs should suffice. Once you're inside the
>> board code, passing stuff around as C parameters is probably an
>> improvement over passing around QemuOpts.
>>
>> > * adding "slots" readonly property to i440fx & q35 for consumption in
>> > ACPI hotplug code and building ACPI tables. It would be
>> > essentially another
>> > global lookup for i440fx & q35 object and pulling "slots" property,
>> > which is much longer way/complex way to get global value. That's a lot
>> > of
>> > boilerplate code for the same outcome.
>>
>> Can't say without seeing the code.
>>
>> > * about setting default for "mem" value: if default "mem" is not set and
>> > no -m is provided on CLI, we get case where
>> > ram_size = foo & "mem" unset
>> > And if I recall correctly there was an effort to provide interface for
>> > currently used QemuOpts to external users. So "mem" would get
>> > inconsistent
>> > with what QEMU uses.
>>
>> QemuOpts do not record what QEMU uses. They record what the user asked
>> for.
>>
>> > To sum up above said:
>> > * I'd like to continue using QemuOpts as global constant value store, it
>> > saves from adding a lot of boilerplate-code that would do the same.
>>
>> Keeping the user's configuration just in QemuOpts is fine. What I don't
>> like is messing with it there. This includes storing defaults.
>>
>> Here's another reason: -writeconfig should write out exactly the user's
>> configuration. If you mess with it, it may write out messed up
>> configuration, depending on *when* you mess with it.
>>
>> > Doing
>> > "git grep qemu_get_machine_opts"
>> > gets us several precedents that already use it that way.
>>
>> Note that it does *not* store defaults in QemuOpts, it only creates
>> empty opts. I'm not sure that was a good idea.
> I've dropped completely defaults setting in QemuOpts please see:
> "[PATCH 04/28] vl: convert -m to QemuOpts"
> "[PATCH 05/28] vl.c: extend -m option to support options for memory hotplug"
>
> As for ">it only creates empty opts." I'm confused.
> qemu_opt_get(qemu_get_machine_opts(), "foo") pattern showed by grep is
> the same
> as I use to get "slots/maxmem":
>
> exec.c: if (!qemu_opt_get_bool(qemu_get_machine_opts(), "mem-merge",
> true)) {
> hw/arm/boot.c: info->dtb_filename =
> qemu_opt_get(qemu_get_machine_opts(), "dtb");
> hw/ppc/spapr.c: const char *drivename =
> qemu_opt_get(qemu_get_machine_opts(), "nvram");
> hw/ppc/virtex_ml507.c: dtb_filename =
> qemu_opt_get(qemu_get_machine_opts(), "dtb");
> include/sysemu/sysemu.h:QemuOpts *qemu_get_machine_opts(void);
> kvm-all.c: if (!qemu_opt_get_bool(qemu_get_machine_opts(),
> "kernel_irqchip", true) ||
> target-i386/kvm.c: shadow_mem = qemu_opt_get_size(qemu_get_machine_opts(),
>
> probably it is there because passing them as C parameters is more
> intrusive than
> just using user supplied values directly.
qemu_get_machine_opts() is precedent for factoring out common
opts-querying code.
It has one aspect that may have been a bad idea: it creates empty
machine opts when the user didn't specify any option creating machine
opts.
Hope this unconfuses you. If not, I guess we should just move on to
discussing your revised patch :)
>> > * I believe that setting default in QemuOpts for "mem" is a good thing
>> > that
>> > leads to consistent meaning of "mem" with what QEMU actually uses.
>>
>> I'm not sure I got this argument.
> I can easily drop this hunk from "[PATCH 04/28] vl: convert -m to QemuOpts",
> I've posted tonight as reply to this thread,
> since ram_size is already passed to machine_init(), it's not worth arguing.
Okay.
