Re: [PATCH v2 2/2] scsi: core: Introduce a new list for SCSI proc directory entries

[Mike Christie <michael.christie@oracle.com>]

On 8/30/22 4:05 PM, Bart Van Assche wrote:
> Instead of using scsi_host_template members to track the SCSI proc
> directory entries, track these entries in a list. This patch changes the
> time needed for looking up the proc dir pointer from O(1) into O(n). I
> think this is acceptable since the number of SCSI host adapter types per
> host is usually small (less than ten).
> 
> This patch has been tested by attaching two USB storage devices to a
> qemu host:
> 


>  }
> @@ -149,15 +214,17 @@ void scsi_proc_hostdir_rm(struct scsi_host_template *sht)
>  void scsi_proc_host_add(struct Scsi_Host *shost)
>  {
>  	struct scsi_host_template *sht = shost->hostt;
> +	struct scsi_proc_entry *e;
>  	struct proc_dir_entry *p;
>  	char name[10];
>  
> -	if (!sht->proc_dir)


>   */
>  void scsi_proc_host_rm(struct Scsi_Host *shost)
>  {
> +	struct scsi_proc_entry *e;
>  	char name[10];
>  
> -	if (!shost->hostt->proc_dir)


Hey Bart, Would it better to replace those two checks with a

if (!sht->show_info)
	return;

like is done in scsi_proc_hostdir_add/scsi_proc_hostdir_rm? In those
hostdir functions if show_info is not set, you will not add an entry to
scsi_proc_list. So in the above functions if that callout is not set
you know there is no entry on &scsi_proc_list and don't need to grab the
global_host_template_mutex for those cases.

I can't really test but someone did say they had 1000s of scsi_hosts for
iscsi. I'm not really sure how big a deal it is since we wouldn't be
doing a lot of work with that mutex hold, but it seems like a simple and
nice change just in case.