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

[Markus Armbruster]

Markus Armbruster <armbru@redhat.com> writes:

> 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?

2.5. Does the device look like a zoned device to the guest?

> 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?
>
> [...]