Re: [PATCH] esp: fix migration version check in esp_is_version_5()

From: Paolo Bonzini <pbonzini@redhat.com>
To: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>,
	qemu-devel@nongnu.org, laurent@vivier.eu, hpoussin@reactos.org
Subject: Re: [PATCH] esp: fix migration version check in esp_is_version_5()
Date: Mon, 14 Jun 2021 10:15:22 +0200	[thread overview]
Message-ID: <7c83e6b3-4230-b700-15fc-5462c84df3f9@redhat.com> (raw)
In-Reply-To: <20210613102614.5438-1-mark.cave-ayland@ilande.co.uk>

On 13/06/21 12:26, Mark Cave-Ayland wrote:
> Commit 4e78f3bf35 "esp: defer command completion interrupt on incoming data
> transfers" added a version check for use with VMSTATE_*_TEST macros to allow
> migration from older QEMU versions. Unfortunately the version check fails to
> work in its current form since if the VMStateDescription version_id is
> incremented, the test returns false and so the fields are not included in the
> outgoing migration stream.
> 
> Change the version check to use >= rather == to ensure that migration works
> correctly when the ESPState VMStateDescription has version_id > 5.
> 
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> Fixes: 4e78f3bf35 ("esp: defer command completion interrupt on incoming data transfers")
> ---
>   hw/scsi/esp.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
> index bfdb94292b..39756ddd99 100644
> --- a/hw/scsi/esp.c
> +++ b/hw/scsi/esp.c
> @@ -1120,7 +1120,7 @@ static bool esp_is_version_5(void *opaque, int version_id)
>       ESPState *s = ESP(opaque);
>   
>       version_id = MIN(version_id, s->mig_version_id);
> -    return version_id == 5;
> +    return version_id >= 5;
>   }
>   
>   int esp_pre_save(void *opaque)
> 

You can use the _V version of the macros and get rid of this function 
altogether.  VMSTATE_FIFO8_TEST is not used outside esp.c so it can also 
be replaced with VMSTATE_FIFO8_V, just initializing .version_id in place 
of .field_exists.

Paolo