Re: [PATCH v4 00/14] hw/block/nvme: Support Namespace Types and Zoned Namespace Command Set

[Klaus Jensen]

On Sep 24 03:20, Dmitry Fomichev wrote:
> v3 -> v4
> 
>  - Fix bugs introduced in v2/v3 for QD > 1 operation. Now, all writes
>    to a zone happen at the new write pointer variable, zone->w_ptr,
>    that is advanced right after submitting the backend i/o. The existing
>    zone->d.wp variable is updated upon the successful write completion
>    and it is used for zone reporting. Some code has been split from
>    nvme_finalize_zoned_write() function to a new function,
>    nvme_advance_zone_wp().
> 

Same approach that I've used, +1.

>  - Make the code compile under mingw. Switch to using QEMU API for
>    mmap/msync, i.e. memory_region...(). Since mmap is not available in
>    mingw (even though there is mman-win32 library available on Github),
>    conditional compilation is added around these calls to avoid
>    undefined symbols under mingw. A better fix would be to add stub
>    functions to softmmu/memory.c for the case when CONFIG_POSIX is not
>    defined, but such change is beyond the scope of this patchset and it
>    can be made in a separate patch.
> 

Ewwww.

This feels like a hack or at the very least an abuse of the physical
memory management API.

If it really needs to be memory mapped, then I think a hostmem-based
approach similar to what Andrzej did for PMR is needed (I think that
will get rid of the CONFIG_POSIX ifdef at least, but still leave it
slightly tricky to get it to work on all platforms AFAIK). But really,
since we do not require memory semantics for this, then I think the
abstraction is fundamentally wrong.

I am, of course, blowing my own horn, since my implementation uses a
portable blockdev for this.

Another issue is the complete lack of endian conversions. Does it
matter? It depends. Will anyone ever use this on a big endian host and
move the meta data backing file to a little endian host? Probably not.
So does it really matter? Probably not, but it is cutting corners.

>  - Make the list of review comments addressed in v2 of the series
>    (see below).
> 

Very detailed! Thanks!

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