Re: [PATCH 1/4] scsi: core: constify pointer to scsi_host_template

[John Garry]

On 08/04/2022 20:31, Ewan D. Milne wrote:
> On Fri, 2022-04-08 at 13:57 +0100, John Garry wrote:
> > On 08/04/2022 13:32, Krzysztof Kozlowski wrote:
> > > On 08/04/2022 14:14, John Garry wrote:
> > > > On 08/04/2022 11:30, Krzysztof Kozlowski wrote:
> > > > > Several pointers to 'struct scsi_host_template' do not modify it, so
> > > > > made them const for safety.
> > > > Is this standard practice? What is so special here?
> > > This is standard practice and there is nothing special here. Pointers to
> > > const are preferred because:
> > > 1. They add safety if data is actually const. This is not yet the case,
> > > but scsi_host_template allocation could be made const with some effort.
>
> This seems unlikely, because some drivers, e.g. vmw_pvscsi and scsi_debug,
> modify the scsi_host_template based on things like module parameters.

The standard flow is:

shost = scsi_host_alloc(sht, )

// modify shost, like
shost->cmd_per_lun = 5;

scsi_add_host(shost)

Is there some reason for which those two drivers can't follow that?

> > To me this seems better, but I think that some drivers might modify
> > their scsi_host_template (so not possible)
>
> Several drivers modify scsi_host_template, e.g. .can_queue, .cmd_per_lun
>
> There is also code in lpfc_create_port() that initializes a scsi_host_template
> that is embedded in the lpfc_hba struct.  I don't think it gets modified after
> scsi_add_host() but it seems like driver maintainers might expect to be able
> to do so, in general.

Even so, I don't see why other drivers cannot declare their 
scsi_host_template as const. C would have no problem with sht not be 
being const for this:

struct Scsi_Host *scsi_host_alloc(const struct scsi_host_template *sht, )

thanks,
John