Re: [PATCH v6 8/8] tests/qtest/nvme-test: add migration test with full CQ

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Apr 28, 2026 at 05:55:12PM +0200, Alexander Mikhalitsyn wrote:
> Am Mo., 27. Apr. 2026 um 22:00 Uhr schrieb Stefan Hajnoczi
> > On Sun, Apr 19, 2026 at 03:01:39PM +0200, Alexander Mikhalitsyn wrote:
> > > +
> > > +        #define GUEST_MEM_READB(field) \
> > > +                            qtest_readb(ctrl->pdev->bus->qts, (uint64_t)&(field))
> > > +
> > > +        g_assert_cmpint(GUEST_MEM_READB(reqs[i].phys_identify->ieee[0]), ==, 0x0);
> >
> > I was trying to figure out why phys_identify has a pointer type although
> > it is a guest memory address that cannot be dereferenced in C code. I
> > guess the reason is so that the GUEST_MEM_READB() macro can use the
> > address-of operator instead of explicitly calculating the offset of
> > ieee[0], ieee[1], etc? I found this confusing and potentially dangerous
> > (the compiler won't stop the pointer from being dereferenced if someone
> > does it by mistake).
> 
> Exactly, that was my intention, to be able to use address-of operation
> in conjunction
> with structure-dereference operator. To prevent accidental mistakes, I
> used "phys_"
> prefix in structure member names (like "cq->phys_cqe" or
> "reqs[i].phys_identify").
> 
> >
> > It took more time to review the pointer trick than the straightforward
> > approach would have taken. I'd avoid it, but it's a question of coding
> > style and up to you.
> 
> No problem, I think the fact that this code confused you means that my idea
> wasn't that good as I thought ;-) I think I should then change a type for
> phys_identify and phys_cqe to u64 and then add explicit address arithmetic
> or continue to use "arrow" operator but in a special macro like
> GUEST_MEM_READ_SOMETHING(...).
> WDYT?

Encapsulating the address-of operator trick inside a macro would be a
nice solution. By localizing the pointer type just within the macro,
it's more obvious what the intention is and the rest of the program uses
the uint64_t type.

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