linux-kernel - Re: [PATCH 2/2] virt: vmgenid: add support for generation counter

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Date:   Wed, 3 Aug 2022 19:58:58 +0200
From:   "Chalios, Babis" <bchalios@...zon.es>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     <linux-kernel@...r.kernel.org>, <tytso@....edu>, <Jason@...c4.com>,
        <dwmw@...zon.co.uk>, <graf@...zon.de>, <xmarcalx@...zon.co.uk>,
        "Michael S. Tsirkin" <mst@...hat.com>, <ani@...sinha.ca>,
        <imammedo@...hat.com>
Subject: Re: [PATCH 2/2] virt: vmgenid: add support for generation counter



On 3/8/22 17:31, Greg KH wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
>
>
>
> On Wed, Aug 03, 2022 at 05:21:27PM +0200, bchalios@...zon.es wrote:
>> +     /* Backwards compatibility. If CTRA is not there we just don't expose
>> +      * the char device
> Backwards compatibility with what?
With hypervisor versions that do not support the generation counter, but 
do support
the VM generation ID. In this case the hypervisor would expose ADDR but 
not CTRA.
>
>> +      */
>> +     ret = parse_vmgenid_address(device, "CTRA", &state->gen_cntr_addr);
>> +     if (ret)
>> +             return 0;
>> +
>> +     state->next_counter = devm_memremap(&device->dev, state->gen_cntr_addr,
>> +                     sizeof(u32), MEMREMAP_WB);
>> +     if (IS_ERR(state->next_counter))
>> +             return 0;
> This too is an error, you can not return with "all is good", right?
> Once you try to create this device because the address is present, you
> can't just give up and succeed no matter what went wrong, that seems
> incorrect.
Same intention as in the response in your other comment. I thought that 
it doesn't make sense
to fail the whole ACPI device if registering the misc device fails.

However, seeing that again (even if my thinking is right) if this 
devm_memremap fails we should
probably fail because there might be something wrong with the address 
the device gave us.
>
> thanks,
>
> greg k-h


Cheers,
Babis
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