linux-kernel - Re: [PATCH 1/4] scsi: core: constify pointer to scsi_host

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Date:   Mon, 25 Apr 2022 14:04:54 +0100
From:   John Garry <john.garry@...wei.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Christoph Hellwig <hch@...radead.org>
CC:     "Ewan D. Milne" <emilne@...hat.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Alim Akhtar" <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "Doug Gilbert" <dgilbert@...erlog.com>,
        <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <james.smart@...adcom.com>
Subject: Re: [PATCH 1/4] scsi: core: constify pointer to scsi_host_template

On 25/04/2022 10:22, Krzysztof Kozlowski wrote:
> On 25/04/2022 10:58, John Garry wrote:
>> On 20/04/2022 08:03, Christoph Hellwig wrote:
>>>> 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?
>>> I think they should.  Method tables should not be mutable data.
>>> .
>>
>> Hi Krzysztof,
>>
>> Do you have any interest in going further with your work and trying to
>> change all SCSI driver instances of scsi_host_template to be const? I am
>> not sure if it has been attempted before...
> 
> I can work on this, but what about the SCSI core modifying the template?

I hope that this isn't a can of worms...

> For example scsi_proc_hostdir_rm(): 'present' and 'proc_dir' members.
> Where should they be stored? Should they be moved to the Scsi_Host?
> 

I don't think scsi_Host is appropriate as this is per-scsi host 
template, unless you see a way to do it that way. Alternatively we could 
keep a separate list of registered sht, like this:

struct sht_proc_dir {
	int cnt;
	struct list_head list;
	struct proc_dir_entry *proc_dir;
	struct scsi_host_template *sht;
};
static LIST_HEAD(sht_proc_dir_list);

void scsi_proc_hostdir_add(struct scsi_host_template *sht)
{
	struct sht_proc_dir *dir;

	if (!sht->show_info)
		return;

	mutex_lock(&global_host_template_mutex);
	list_for_each_entry(dir, &sht_proc_dir_list, list) {
		if (dir->sht == sht) {
			dir->cnt++;
			goto out;
		}
	}
	dir = kzalloc(sizeof(*dir), GFP_KERNEL);
	if (!dir)
		goto out;

	dir->proc_dir = proc_mkdir(sht->proc_name, proc_scsi);
	if (!dir->proc_dir) {
		printk(KERN_ERR "%s: proc_mkdir failed for %s\n",
			       __func__, sht->proc_name);
		kfree(dir);
		goto out;
	}

	dir->cnt++;
	list_add_tail(&dir->list, &sht_proc_dir_list);
out:
	mutex_unlock(&global_host_template_mutex);
}

and so on..

--->8---

Thanks,
John