linux-kernel - Re: [PATCH RFC v3 03/22] scsi: core: Implement reserved command handling

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Date:   Thu, 27 Oct 2022 09:16:37 +0100
From:   John Garry <john.garry@...wei.com>
To:     Hannes Reinecke <hare@...e.de>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        <axboe@...nel.dk>, <jejb@...ux.ibm.com>,
        <martin.petersen@...cle.com>, <jinpu.wang@...ud.ionos.com>,
        <bvanassche@....org>, <hch@....de>, <ming.lei@...hat.com>,
        <niklas.cassel@....com>
CC:     <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-ide@...r.kernel.org>, <linux-scsi@...r.kernel.org>,
        <linuxarm@...wei.com>
Subject: Re: [PATCH RFC v3 03/22] scsi: core: Implement reserved command
 handling

On 27/10/2022 08:51, Hannes Reinecke wrote:
>>>
>>> Signed-off-by: Hannes Reinecke <hare@...e.de>
>>> #jpg: Set tag_set->queue_depth = shost->can_queue, and not
>>> = shost->can_queue + shost->nr_reserved_cmds;
>>> Signed-off-by: John Garry <john.garry@...wei.com>
>>> ---
>>>   drivers/scsi/hosts.c     |  3 +++
>>>   drivers/scsi/scsi_lib.c  |  2 ++
>>>   include/scsi/scsi_host.h | 15 ++++++++++++++-
>>>   3 files changed, 19 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
>>> index 12346e2297fd..db89afc37bc9 100644
>>> --- a/drivers/scsi/hosts.c
>>> +++ b/drivers/scsi/hosts.c
>>> @@ -489,6 +489,9 @@ struct Scsi_Host *scsi_host_alloc(struct 
>>> scsi_host_template *sht, int privsize)
>>>       if (sht->virt_boundary_mask)
>>>           shost->virt_boundary_mask = sht->virt_boundary_mask;
>>> +    if (sht->nr_reserved_cmds)
>>> +        shost->nr_reserved_cmds = sht->nr_reserved_cmds;
>>> +
>>
>> Nit: the if is not really necessary I think. But it does not hurt.
>>
> Yes, we do.
> Not all HBAs are able to figure out the number of reserved commands 
> upfront; some modify that based on the PCI device used etc.
> So I'd keep it for now.

I think logically Damien is right as in the shost alloc 
shost->nr_reserved_cmds is initially zero, so:

if (sht->nr_reserved_cmds)
        shost->nr_reserved_cmds = sht->nr_reserved_cmds;

is same as simply:

	shost->nr_reserved_cmds = sht->nr_reserved_cmds;

However I am just copying the coding style.

Thanks,
John