Re: [PATCH RFC v2 02/18] scsi: core: Resurrect scsi_{get,free}_host_dev()

[John Garry]

On 14/06/2022 20:33, Bart Van Assche wrote:

Hi Bart,

> On 6/9/22 03:29, John Garry wrote:
> > +/**
> > + * scsi_get_host_dev - Create a scsi_device that points to the host 
> > adapter itself
>                                                 
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> What does this mean? That part of the function description is not
> clear to me.

Agreed, this text is just as it was before (it was originally deleted) 
but I can fix it up to make sense.

> > + * @shost: Host that needs a scsi_device
>                                ^^^^^^^^^^^^^
> This is not detailed enough. Consider changing "a scsi_device" into
> "a scsi device for allocating reserved commands from".
>
> > + *
> > + * Lock status: None assumed.
> > + *
> > + * Returns:     The scsi_device or NULL
> > + *
> > + * Notes:
> > + *    Attach a single scsi_device to the Scsi_Host - this should
> > + *    be made to look like a "pseudo-device" that points to the
> > + *    HA itself.
> > + *
> > + *    Note - this device is not accessible from any high-level
> > + *    drivers (including generics), which is probably not
> > + *    optimal.  We can add hooks later to attach.
>
> The "which is probably not optimal. We can add hooks later to attach."
> part probably should be moved to the patch description.

ok

> > + */
> > +struct scsi_device *scsi_get_host_dev(struct Scsi_Host *shost)
> > +{
> > +    struct scsi_device *sdev = NULL;
> > +    struct scsi_target *starget;
> > +
> > +    mutex_lock(&shost->scan_mutex);
> > +    if (!scsi_host_scan_allowed(shost))
> > +        goto out;
> > +    starget = scsi_alloc_target(&shost->shost_gendev, 0, 
> > shost->this_id);
>                                                            
> ^^^^^^^^^^^^^^^^^^
> Is it guaranteed that this channel / id combination will not be used for
> any other SCSI device?

Does it matter if the parent device is different?

> What if shost->this_id == -1?
>
> > +    if (!starget)
> > +        goto out;
> > +
> > +    sdev = scsi_alloc_sdev(starget, 0, NULL);
> > +    if (sdev)
> > +        sdev->borken = 0;
> > +    else
> > +        scsi_target_reap(starget);
> > +    put_device(&starget->dev);
> > + out:
> > +    mutex_unlock(&shost->scan_mutex);
> > +    return sdev;
> > +}
> > +EXPORT_SYMBOL(scsi_get_host_dev);
>
> Elsewhere in the SCSI core "get..dev" means increment the reference 
> count of
> a SCSI device. Maybe scsi_alloc_host_dev() is a better name?

I think that the intention is to only use this once for a shost, i.e. 
get or allocate that scsi_device once and use it for the lifetime of the 
shost. But I can rename if you think it's better.

> > +/*
> > + * These two functions are used to allocate and free a pseudo device
> > + * which will connect to the host adapter itself rather than any
> > + * physical device.  You must deallocate when you are done with the
> > + * thing.  This physical pseudo-device isn't real and won't be available
> > + * from any high-level drivers.
> > + */
>
> Please keep function comments in .c files because that makes it more likely
> that the comment and the implementation will remain in sync.

fine, I can relocate this.

Thanks,
John