Re: [PATCH v3 09/15] vfio/ap: Use vfio_[attach/detach]_device

[Matthew Rosato]

On 10/4/23 5:58 AM, Eric Auger wrote:
> Hi Cédric,
> 
> On 10/3/23 17:25, Cédric Le Goater wrote:
>> On 10/3/23 12:14, Eric Auger wrote:
>>> Let the vfio-ap device use vfio_attach_device() and
>>> vfio_detach_device(), hence hiding the details of the used
>>> IOMMU backend.
>>>
>>> We take the opportunity to use g_path_get_basename() which
>>> is prefered, as suggested by
>>> 3e015d815b ("use g_path_get_basename instead of basename")
>>>
>>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
>>>
>>> ---
>>>
>>> v2 -> v3:
>>> - Mention g_path_get_basename in commit message and properly free
>>>    vbasedev->name, call vfio_detach_device
>>> ---
>>>   hw/vfio/ap.c | 70 ++++++++++------------------------------------------
>>>   1 file changed, 13 insertions(+), 57 deletions(-)
>>>
>>> diff --git a/hw/vfio/ap.c b/hw/vfio/ap.c
>>> index 6e21d1da5a..d0b587b3b1 100644
>>> --- a/hw/vfio/ap.c
>>> +++ b/hw/vfio/ap.c
>>> @@ -53,40 +53,6 @@ struct VFIODeviceOps vfio_ap_ops = {
>>>       .vfio_compute_needs_reset = vfio_ap_compute_needs_reset,
>>>   };
>>>   -static void vfio_ap_put_device(VFIOAPDevice *vapdev)
>>> -{
>>> -    g_free(vapdev->vdev.name);
>>> -    vfio_put_base_device(&vapdev->vdev);
>>> -}
>>> -
>>> -static VFIOGroup *vfio_ap_get_group(VFIOAPDevice *vapdev, Error **errp)
>>> -{
>>> -    GError *gerror = NULL;
>>> -    char *symlink, *group_path;
>>> -    int groupid;
>>> -
>>> -    symlink = g_strdup_printf("%s/iommu_group", vapdev->vdev.sysfsdev);
>>> -    group_path = g_file_read_link(symlink, &gerror);
>>> -    g_free(symlink);
>>> -
>>> -    if (!group_path) {
>>> -        error_setg(errp, "%s: no iommu_group found for %s: %s",
>>> -                   TYPE_VFIO_AP_DEVICE, vapdev->vdev.sysfsdev,
>>> gerror->message);
>>> -        g_error_free(gerror);
>>> -        return NULL;
>>> -    }
>>> -
>>> -    if (sscanf(basename(group_path), "%d", &groupid) != 1) {
>>> -        error_setg(errp, "vfio: failed to read %s", group_path);
>>> -        g_free(group_path);
>>> -        return NULL;
>>> -    }
>>> -
>>> -    g_free(group_path);
>>> -
>>> -    return vfio_get_group(groupid, &address_space_memory, errp);
>>> -}
>>> -
>>>   static void vfio_ap_req_notifier_handler(void *opaque)
>>>   {
>>>       VFIOAPDevice *vapdev = opaque;
>>> @@ -189,22 +155,15 @@ static void
>>> vfio_ap_unregister_irq_notifier(VFIOAPDevice *vapdev,
>>>   static void vfio_ap_realize(DeviceState *dev, Error **errp)
>>>   {
>>>       int ret;
>>> -    char *mdevid;
>>>       Error *err = NULL;
>>> -    VFIOGroup *vfio_group;
>>>       APDevice *apdev = AP_DEVICE(dev);
>>>       VFIOAPDevice *vapdev = VFIO_AP_DEVICE(apdev);
>>> +    VFIODevice *vbasedev = &vapdev->vdev;
>>>   -    vfio_group = vfio_ap_get_group(vapdev, errp);
>>> -    if (!vfio_group) {
>>> -        return;
>>> -    }
>>> -
>>> -    vapdev->vdev.ops = &vfio_ap_ops;
>>> -    vapdev->vdev.type = VFIO_DEVICE_TYPE_AP;
>>> -    mdevid = basename(vapdev->vdev.sysfsdev);
>>> -    vapdev->vdev.name = g_strdup_printf("%s", mdevid);
>>> -    vapdev->vdev.dev = dev;
>>> +    vbasedev->name = g_path_get_basename(vbasedev->sysfsdev);
>>> +    vbasedev->ops = &vfio_ap_ops;
>>> +    vbasedev->type = VFIO_DEVICE_TYPE_AP;
>>> +    vbasedev->dev = dev;
>>>         /*
>>>        * vfio-ap devices operate in a way compatible with discarding of
>>> @@ -214,9 +173,11 @@ static void vfio_ap_realize(DeviceState *dev,
>>> Error **errp)
>>>        */
>>>       vapdev->vdev.ram_block_discard_allowed = true;
>>>   -    ret = vfio_get_device(vfio_group, mdevid, &vapdev->vdev, errp);
>>> +    ret = vfio_attach_device(vbasedev->name, vbasedev,
>>> +                             &address_space_memory, errp);
>>>       if (ret) {
>>> -        goto out_get_dev_err;
>>> +        g_free(vbasedev->name);
>>> +        return;
>>>       }
>>>         vfio_ap_register_irq_notifier(vapdev, VFIO_AP_REQ_IRQ_INDEX,
>>> &err);
>>> @@ -225,25 +186,20 @@ static void vfio_ap_realize(DeviceState *dev,
>>> Error **errp)
>>>            * Report this error, but do not make it a failing condition.
>>>            * Lack of this IRQ in the host does not prevent normal
>>> operation.
>>>            */
>>> +        vfio_detach_device(vbasedev);
>>>           error_report_err(err);
>>> +        g_free(vbasedev->name);
>>>       }
>>> -
>>> -    return;
>>> -
>>> -out_get_dev_err:
>>> -    vfio_ap_put_device(vapdev);
>>> -    vfio_put_group(vfio_group);
>>>   }
>>
>>
>> To be consistent with vfio_(pci)_realize(), I would introduce the same
>> failure path at the end the routine :
>>
>>   out_detach:
>>       vfio_detach_device(vbasedev);
>>   error:
>>       error_prepend(errp, VFIO_MSG_PREFIX, vbasedev->name);
>>       g_free(vbasedev->name);
>>
>>
>> and add the VFIO_MSG_PREFIX while we are at it.
> 
> following Matthew's comment we do not have any need for error handling
> in vfio_ap_realize() anymore.
> 
> so just removing the improper additions:
> +        vfio_detach_device(vbasedev);
> +        g_free(vbasedev->name);
> 
> Thanks

Just to clarify, there is still a little error handling needed for the error 
case on vfio_attach_device(), in that case you are passing errp into 
vfio_attach_device and that should have an error propogated when ret!=0, 
meaning we won't get the dc->unrealize() later.  Device wasn't attached, but we 
did allocate memory for vbasedev->name already so we need to undo that part 
ourselves.  That could be inline (as you do already in this patch) or, if you 
choose to add the VFIO_MSG_PREFIX it might make sense to put it in an error: 
label as Cedric suggested for additional later use.  FWIW, I'm fine with either 
but here's a snippet of what I mean for the sake of clarity:


Approach 1 (w/ new prepend):

    ret = vfio_attach_device(vbasedev->name, vbasedev,
                             &address_space_memory, errp);
    if (ret) {
        goto error;
    }

    vfio_ap_register_irq_notifier(vapdev, VFIO_AP_REQ_IRQ_INDEX, &err);
    if (err) {
        /*
         * Report this error, but do not make it a failing condition.
         * Lack of this IRQ in the host does not prevent normal operation.
         */
        error_report_err(err);
    }

    return;

error:
    error_prepend(errp, VFIO_MSG_PREFIX, vbasedev->name);
    g_free(vbasedev->name);


Approach 2 (no prepend):

    ret = vfio_attach_device(vbasedev->name, vbasedev,
                             &address_space_memory, errp);
    if (ret) {
        g_free(vbasedev->name);
        return;
    }

    vfio_ap_register_irq_notifier(vapdev, VFIO_AP_REQ_IRQ_INDEX, &err);
    if (err) {
        /*
         * Report this error, but do not make it a failing condition.
         * Lack of this IRQ in the host does not prevent normal operation.
         */
        error_report_err(err);
    }

    return;


With either of these approaches:

Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>

Thanks,
Matt

> 
> Eric
>>
>> This is minor, so :
>>
>> Reviewed-by: Cédric Le Goater <clg@redhat.com>
>>
>> Thanks,
>>
>> C.
>>
>>
>>
>>>     static void vfio_ap_unrealize(DeviceState *dev)
>>>   {
>>>       APDevice *apdev = AP_DEVICE(dev);
>>>       VFIOAPDevice *vapdev = VFIO_AP_DEVICE(apdev);
>>> -    VFIOGroup *group = vapdev->vdev.group;
>>>         vfio_ap_unregister_irq_notifier(vapdev, VFIO_AP_REQ_IRQ_INDEX);
>>> -    vfio_ap_put_device(vapdev);
>>> -    vfio_put_group(group);
>>> +    vfio_detach_device(&vapdev->vdev);
>>> +    g_free(vapdev->vdev.name);
>>>   }
>>>     static Property vfio_ap_properties[] = {
>>
>