linux-kernel - Re: Antw: [EXT] Re: [PATCH] scsi scsi_transport_iscsi.c: fix misuse of %llu in scsi_transport

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Date:   Tue, 12 Oct 2021 09:04:28 +0200
From:   "Ulrich Windl" <Ulrich.Windl@...uni-regensburg.de>
To:     <jejb@...ux.ibm.com>, <martin.petersen@...cle.com>,
        "Chris Leech" <cleech@...hat.com>, <qtxuning1999@...u.edu.cn>,
        "Lee Duncan" <lduncan@...e.com>
Cc:     "open-iscsi" <open-iscsi@...glegroups.com>,
        <linux-kernel@...r.kernel.org>, <linux-scsi@...r.kernel.org>
Subject: Re: Antw: [EXT] Re: [PATCH] scsi scsi_transport_iscsi.c: fix
 misuse of %llu in scsi_transport_iscsi.c

>>> Mike Christie <michael.christie@...cle.com> schrieb am 11.10.2021 um 17:29 in
Nachricht <ae7a82c2-5b19-493a-8d61-cdccb00cf46c@...cle.com>:
> On 10/11/21 1:35 AM, Ulrich Windl wrote:
>>>>> Joe Perches <joe@...ches.com> schrieb am 09.10.2021 um 05:14 in Nachricht
>> <5daf69b365e23ceecee911c4d0f2f66a0b9ec95c.camel@...ches.com>:
>>> On Sat, 2021-10-09 at 11:02 +0800, Guo Zhi wrote:
>>>> Pointers should be printed with %p or %px rather than
>>>> cast to (unsigned long long) and printed with %llu.
>>>> Change %llu to %p to print the pointer into sysfs.
>>> ][]
>>>> diff --git a/drivers/scsi/scsi_transport_iscsi.c 
>>> b/drivers/scsi/scsi_transport_iscsi.c
>>> []
>>>> @@ -129,8 +129,8 @@ show_transport_handle(struct device *dev, struct 
>>> device_attribute *attr,
>>>>  
>>>>
>>>>  	if (!capable(CAP_SYS_ADMIN))
>>>>  		return -EACCES;
>>>> -	return sysfs_emit(buf, "%llu\n",
>>>> -		  (unsigned long long)iscsi_handle(priv->iscsi_transport));
>>>> +	return sysfs_emit(buf, "%p\n",
>>>> +		iscsi_ptr(priv->iscsi_transport));
>>>
>>> iscsi_transport is a pointer isn't it?
>>>
>>> so why not just
>>>
>>> 	return sysfs_emit(buf, "%p\n", priv->iscsi_transport);
>> 
>> Isn't the difference that %p outputs hex, while %u outputs decimal?
>> 
> 
> Yeah, I think this patch will break userspace, because it doesn't know it's
> a pointer. It could be doing:
> 
> sscanf(str, "%llu", &val);
> 
> The value is just later passed back to the kernel to look up a driver in
> iscsi_if_transport_lookup:
> 
>         list_for_each_entry(priv, &iscsi_transports, list) {
>                 if (tt == priv->iscsi_transport) {
> 
> so we could just replace priv->transport with an int and use an ida to assign
> the value.

I'm not in the details, but if that value is used as an ID, shouldn't it have been something like "ID%llu" right from the start?
If so it would be rather easy to use "ID%p" instead (if the syntax of the ID is left unspecified). At least nobody would treat it as a number.

Regards,
Ulrich


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