Dropped/disabled NVME support in qemu

[Guenter Roeck]

Hi all,

since qemu v5.1, nvme support has been dropped from several architectures.
Well, it was not exactly dropped, but disabled.

On those architectures, trying to boot from an nvme drive now results
in the following or a similar error message.

qemu-system-alpha: -device nvme,serial=foo,drive=d0: MSI-X is not supported by 
interrupt controller

This is the result of the following two commits.

fbf2e5375e ("hw/block/nvme: Verify msix_vector_use() returned value")
1c0c2163aa ("hw/block/nvme: verify msix_init_exclusive_bar() return value")

Affected architectures are alpha, parisc, ppc, sh, and sparc, and every other
architecture/platform where the interrupt controller does not support MSI-X.
After reverting above patches, I can boot from nvme again.

This does not really matter for me - I run my own versions of qemu anyway,
and don't mind carrying reverts if I have to. However, for my education,
I would like to understand why nvme support was disabled, especially since
it seemed to work for me just fine for years. Can someone please explain ?

Thanks,
Guenter