Messages in this thread | | | Subject | Re: [PATCH v3 4/9] s390: ap: tools to find a queue with a specific APQN | From | Tony Krowiak <> | Date | Fri, 22 Feb 2019 10:04:55 -0500 |
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On 2/18/19 7:21 AM, Cornelia Huck wrote: > On Fri, 15 Feb 2019 17:13:21 -0500 > Tony Krowiak <akrowiak@linux.ibm.com> wrote: > >> On 2/14/19 8:51 AM, Pierre Morel wrote: >>> We need to find the queue with a specific APQN during the >>> handling of the interception of the PQAP/AQIC instruction. >>> >>> To handle the AP associated device reference count we keep >>> track of it in the vfio_ap_queue until we put the device. >>> >>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com> >>> --- >>> drivers/s390/crypto/vfio_ap_ops.c | 54 +++++++++++++++++++++++++++++++++++ >>> drivers/s390/crypto/vfio_ap_private.h | 1 + >>> 2 files changed, 55 insertions(+) > >>> +/** >>> + * vfio_ap_get_queue: Retrieve a queue with a specific APQN >>> + * @apqn: The queue APQN >>> + * >>> + * Retrieve a queue with a specific APQN from the list of the >>> + * devices associated to the vfio_ap_driver. >>> + * >>> + * The vfio_ap_queue has been already associated with the device >>> + * during the probe. >>> + * Store the associated device for reference counting >>> + * >>> + * Returns the pointer to the associated vfio_ap_queue >>> + */ >>> +static __attribute__((unused)) >>> + struct vfio_ap_queue *vfio_ap_get_queue(int apqn) >> >> I think you should change this signature for the reasons I stated >> below: >> >> struct device *vfio_ap_get_queue_dev(int apqn) >> >>> +{ >>> + struct device *dev; >>> + struct vfio_ap_queue *q; >>> + >>> + dev = driver_find_device(&matrix_dev->vfio_ap_drv->driver, NULL, &apqn, >>> + vfio_ap_check_apqn); >>> + if (!dev) >>> + return NULL; >>> + q = dev_get_drvdata(dev); >>> + q->dev = dev; >> >> Why store the device with the vfio_ap_queue object? Why not just return >> the device. The caller can get the vfio_ap_queue from the device's >> driver data. It seems the only reason for the 'dev' field is to >> temporarily hold a ref to the device so it can be put later. Why not >> just put the device.
After thinking about this further, I question whether we even need this function if it is going to return 'struct device *'. In that case, why not just call driver_find_device() when the device is needed? If you want to keep the function, then the function needs only one statement:
return driver_find_device(...).
> > Having looked at the remainder of the patches, I tend to agree that we > don't really need the backlink; we walk the driver's list of devices in > any case IIUC. > > We *might* want a mechanism to grab the queue quickly (i.e. without > walking the list) if there's anything performance sensitive in there; > but from the patch descriptions, I don't think anything is done in a > hot path, so it should be fine. >
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