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

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Message-ID: <5485f529-e99a-0bdd-07bd-b5b559da91e6@interlog.com>
Date:   Mon, 25 Apr 2022 21:54:31 -0400
From:   Douglas Gilbert <dgilbert@...erlog.com>
To:     Bart Van Assche <bvanassche@....org>,
        John Garry <john.garry@...wei.com>,
        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>, 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 2022-04-25 21:16, Bart Van Assche wrote:
> On 4/25/22 06:04, John Garry wrote:
>> On 25/04/2022 10:22, Krzysztof Kozlowski wrote:
>>> 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);
>> }
> 
> How about removing scsi_proc_hostdir_add(), scsi_proc_hostdir_rm() and all other 
> code that creates files or directories under /proc/scsi? There should be 
> corresponding entries in sysfs for all /proc/scsi entries. Some tools in 
> sg3_utils use that directory so sg3_utils will have to be updated.

... breaking this:

~$ cat /proc/scsi/scsi

Attached devices:

Host: scsi3 Channel: 00 Id: 00 Lun: 00

   Vendor: IBM-207x Model: HUSMM8020ASS20   Rev: J4B6

   Type:   Direct-Access                    ANSI  SCSI revision: 06

Host: scsi3 Channel: 00 Id: 01 Lun: 00

   Vendor: IBM-207x Model: HUSMM8020ASS20   Rev: J4B6

   Type:   Direct-Access                    ANSI  SCSI revision: 06

Host: scsi3 Channel: 00 Id: 02 Lun: 00

   Vendor: SEAGATE  Model: ST200FM0073      Rev: 0007

   Type:   Direct-Access                    ANSI  SCSI revision: 06
...

A deprecation notice would be helpful, then removal after a few kernel
cycles. Yes, lsscsi can give that output:

$ lsscsi -c

Attached devices:

Host: scsi2 Channel: 00 Target: 00 Lun: 00

   Vendor: SEAGATE  Model: ST200FM0073      Rev: 0007

   Type:   Direct-Access                    ANSI SCSI revision: 06

Host: scsi2 Channel: 00 Target: 01 Lun: 00

   Vendor: WDC      Model: WSH722020AL5204  Rev: C421

   Type:   Zoned Block                      ANSI SCSI revision: 07

Host: scsi2 Channel: 00 Target: 02 Lun: 00

   Vendor: Areca Te Model: ARC-802801.37.69 Rev: 0137

   Type:   Enclosure                        ANSI SCSI revision: 05
...

[Hmmm, in a different order.]

However no distribution that I'm aware of includes lsscsi in its installation.
[Most recent example: Ubuntu 22.04]
Linux is not alone ... in FreeBSD how do you list SCSI devices in your
system? Answer: as root you invoke 'camcontrol devlist', it's so obvious.

Perhaps the Linux kernel could have a deprecation process which uses inotify
or similar to notice accesses to /proc/scsi/scsi (say) and print out
a helpful response along the lines" "this is no longer supported, try using
the lsscsi utility".

Doug Gilbert