Re: [PATCH v8 3/7] block: add block layer APIs resembling Linux ZonedBlockDevice ioctls

[Markus Armbruster]

Sam Li <faithilikerun@gmail.com> writes:

> Markus Armbruster <armbru@redhat.com> 于2022年8月31日周三 16:35写道：
>>
>> Sam Li <faithilikerun@gmail.com> writes:
>>
>> > Markus Armbruster <armbru@redhat.com> 于2022年8月30日周二 19:57写道：
>> >>
>> >> Sam Li <faithilikerun@gmail.com> writes:
>> >>
>> >> > By adding zone management operations in BlockDriver, storage controller
>> >> > emulation can use the new block layer APIs including Report Zone and
>> >> > four zone management operations (open, close, finish, reset).
>> >> >
>> >> > Add zoned storage commands of the device: zone_report(zrp), 
>> >> > zone_open(zo),
>> >> > zone_close(zc), zone_reset(zrs), zone_finish(zf).
>> >> >
>> >> > For example, to test zone_report, use following command:
>> >> > $ ./build/qemu-io --image-opts driver=zoned_host_device, 
>> >> > filename=/dev/nullb0
>> >> > -c "zrp offset nr_zones"
>> >> >
>> >> > Signed-off-by: Sam Li <faithilikerun@gmail.com>
>> >> > Reviewed-by: Hannes Reinecke <hare@suse.de>
>> >>
>> >> [...]
>> >>
>> >> > diff --git a/block/file-posix.c b/block/file-posix.c
>> >> > index 0a8b4b426e..e3efba6db7 100644
>> >> > --- a/block/file-posix.c
>> >> > +++ b/block/file-posix.c
>> >>
>> >> [...]
>> >>
>> >> > @@ -3752,6 +4025,54 @@ static BlockDriver bdrv_host_device = {
>> >> >  #endif
>> >> >  };
>> >> >
>> >> > +#if defined(CONFIG_BLKZONED)
>> >> > +static BlockDriver bdrv_zoned_host_device = {
>> >> > +        .format_name = "zoned_host_device",
>> >>
>> >> Indentation should be 4, not 8.
>> >>
>> >> > +        .protocol_name = "zoned_host_device",
>> >> > +        .instance_size = sizeof(BDRVRawState),
>> >> > +        .bdrv_needs_filename = true,
>> >> > +        .bdrv_probe_device  = hdev_probe_device,
>> >> > +        .bdrv_file_open     = hdev_open,
>> >> > +        .bdrv_close         = raw_close,
>> >> > +        .bdrv_reopen_prepare = raw_reopen_prepare,
>> >> > +        .bdrv_reopen_commit  = raw_reopen_commit,
>> >> > +        .bdrv_reopen_abort   = raw_reopen_abort,
>> >> > +        .bdrv_co_create_opts = bdrv_co_create_opts_simple,
>> >> > +        .create_opts         = &bdrv_create_opts_simple,
>> >> > +        .mutable_opts        = mutable_opts,
>> >> > +        .bdrv_co_invalidate_cache = raw_co_invalidate_cache,
>> >> > +        .bdrv_co_pwrite_zeroes = hdev_co_pwrite_zeroes,
>> >> > +
>> >> > +        .bdrv_co_preadv         = raw_co_preadv,
>> >> > +        .bdrv_co_pwritev        = raw_co_pwritev,
>> >> > +        .bdrv_co_flush_to_disk  = raw_co_flush_to_disk,
>> >> > +        .bdrv_co_pdiscard       = hdev_co_pdiscard,
>> >> > +        .bdrv_co_copy_range_from = raw_co_copy_range_from,
>> >> > +        .bdrv_co_copy_range_to  = raw_co_copy_range_to,
>> >> > +        .bdrv_refresh_limits = raw_refresh_limits,
>> >> > +        .bdrv_io_plug = raw_aio_plug,
>> >> > +        .bdrv_io_unplug = raw_aio_unplug,
>> >> > +        .bdrv_attach_aio_context = raw_aio_attach_aio_context,
>> >> > +
>> >> > +        .bdrv_co_truncate       = raw_co_truncate,
>> >> > +        .bdrv_getlength = raw_getlength,
>> >> > +        .bdrv_get_info = raw_get_info,
>> >> > +        .bdrv_get_allocated_file_size
>> >> > +                            = raw_get_allocated_file_size,
>> >> > +        .bdrv_get_specific_stats = hdev_get_specific_stats,
>> >> > +        .bdrv_check_perm = raw_check_perm,
>> >> > +        .bdrv_set_perm   = raw_set_perm,
>> >> > +        .bdrv_abort_perm_update = raw_abort_perm_update,
>> >> > +        .bdrv_probe_blocksizes = hdev_probe_blocksizes,
>> >> > +        .bdrv_probe_geometry = hdev_probe_geometry,
>> >> > +        .bdrv_co_ioctl = hdev_co_ioctl,
>> >> > +
>> >> > +        /* zone management operations */
>> >> > +        .bdrv_co_zone_report = raw_co_zone_report,
>> >> > +        .bdrv_co_zone_mgmt = raw_co_zone_mgmt,
>> >> > +};
>> >>
>> >> Differences to bdrv_host_device:
>> >>
>> >> * .bdrv_parse_filename is not set
>> >>
>> >> * .bdrv_co_ioctl is not set
>> >>
>> >> * .bdrv_co_zone_report and .bdrv_co_zone_mgmt are set
>> >
>> > As Stefan mentioned, zoned_host_device is a new driver that doesn't
>> > work with string filenames. .bdrv_parse_filename() helps legacy
>> > drivers strip the optional protocol prefix off the filename and no use
>> > here. Therefore it can be dropped.
>>
>> Makes sense.
>>
>> > .bdrv_co_ioctl is set actually.
>>
>> You're right; I diffed the two and misread the result.
>>
>> > Zoned_host_device is basically host_device + zone operations. It
>> > serves for a simple purpose: if the host device is zoned, register
>> > zoned_host_device driver; else, register host_device.
>>
>> Why would I ever want to use host_device instead of zoned_host_device?
>>
>> To answer this question, we need to understand how their behavior
>> differs.
>>
>> We can ignore the legacy protocol prefix / string filename part.
>>
>> All that's left seems to be "if the host device is zoned, then using the
>> zoned_host_device driver gets you the zoned features, whereas using the
>> host_device driver doesn't".  What am I missing?
>
> I think that's basically what users need to know about.

Now answer my previous question, please: why would I ever want to use
host_device instead of zoned_host_device?

Or in other words, why would I ever want to present a zoned host device
to a guest as non-zoned device?

>> >> Notably common is .bdrv_file_open = hdev_open.  What happens when you
>> >> try to create a zoned_host_device where the @filename argument is not in
>> >> fact a zoned device?
>> >
>> > If the device is a regular block device, QEMU will still open the
>> > device. For instance, I use a loopback device to test zone_report in
>> > qemu-io. It returns ENOTTY which indicates Inappropriate ioctl for the
>> > device. Meanwhile, if using a regular block device when emulation a
>> > zoned device on a guest os, the best case is that the guest can boot
>> > but has no emulated block device. In some cases, QEMU just terminates
>> > because the block device has not met the alignment requirements.
>>
>> I'm not sure I understand all of this.  I'm also not sure I have to :)
>
> Maybe I didn't explain it very well. Which part would you like to know
> more about?

Let's try more specific questions.  Say I configure a zoned_host_device
backed by a host device that isn't zoned.

1. Is this configuration accepted?

2. Would a guest work as long as it doesn't touch this device?

3. Would a guest using this device work as long as it uses no zoned
   features?

4. What happens when a guest tries to use zoned features?

[...]