Date:   Tue, 18 Jun 2019 11:31:42 -0400
From:   Douglas Gilbert <dgilbert@...erlog.com>
To:     Marc Gonzalez <marc.w.gonzalez@...e.fr>,
        Finn Thain <fthain@...egraphics.com.au>
Cc:     Bart Van Assche <bvanassche@....org>,
        James Bottomley <jejb@...ux.ibm.com>,
        Martin Petersen <martin.petersen@...cle.com>,
        SCSI <linux-scsi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v1] scsi: Don't select SCSI_PROC_FS by default

On 2019-06-18 3:29 a.m., Marc Gonzalez wrote:
> On 18/06/2019 03:08, Finn Thain wrote:
> 
>> On Mon, 17 Jun 2019, Douglas Gilbert wrote:
>>
>>> On 2019-06-17 5:11 p.m., Bart Van Assche wrote:
>>>
>>>> On 6/12/19 6:59 AM, Marc Gonzalez wrote:
>>>>
>>>>> According to the option's help message, SCSI_PROC_FS has been
>>>>> superseded for ~15 years. Don't select it by default anymore.
>>>>>
>>>>> Signed-off-by: Marc Gonzalez <marc.w.gonzalez@...e.fr>
>>>>> ---
>>>>>    drivers/scsi/Kconfig | 3 ---
>>>>>    1 file changed, 3 deletions(-)
>>>>>
>>>>> diff --git a/drivers/scsi/Kconfig b/drivers/scsi/Kconfig
>>>>> index 73bce9b6d037..8c95e9ad6470 100644
>>>>> --- a/drivers/scsi/Kconfig
>>>>> +++ b/drivers/scsi/Kconfig
>>>>> @@ -54,14 +54,11 @@ config SCSI_NETLINK
>>>>>    config SCSI_PROC_FS
>>>>>        bool "legacy /proc/scsi/ support"
>>>>>        depends on SCSI && PROC_FS
>>>>> -    default y
>>>>>        ---help---
>>>>>          This option enables support for the various files in
>>>>>          /proc/scsi.  In Linux 2.6 this has been superseded by
>>>>>          files in sysfs but many legacy applications rely on this.
>>>>> -      If unsure say Y.
>>>>> -
>>>>>    comment "SCSI support type (disk, tape, CD-ROM)"
>>>>>        depends on SCSI
>>>>
>>>> Hi Doug,
>>>>
>>>> If I run grep "/proc/scsi" over the sg3_utils source code then grep reports
>>>> 38 matches for that string. Does sg3_utils break with SCSI_PROC_FS=n?
>>>
>>> First, the sg driver. If placing
>>> #undef CONFIG_SCSI_PROC_FS
>>>
>>> prior to the includes in sg.c is a valid way to test that then the
>>> answer is no. Ah, but you are talking about sg3_utils .
>>>
>>> Or are you? For sg3_utils:
>>>
>>> $ find . -name '*.c' -exec grep "/proc/scsi" {} \; -print
>>> static const char * proc_allow_dio = "/proc/scsi/sg/allow_dio";
>>> ./src/sg_read.c
>>> static const char * proc_allow_dio = "/proc/scsi/sg/allow_dio";
>>> ./src/sgp_dd.c
>>> static const char * proc_allow_dio = "/proc/scsi/sg/allow_dio";
>>> ./src/sgm_dd.c
>>> static const char * proc_allow_dio = "/proc/scsi/sg/allow_dio";
>>> ./src/sg_dd.c
>>>                  "'echo 1 > /proc/scsi/sg/allow_dio'\n", q_len, dirio_count);
>>> ./testing/sg_tst_bidi.c
>>> static const char * proc_allow_dio = "/proc/scsi/sg/allow_dio";
>>> ./examples/sgq_dd.c
>>>
>>>
>>> That is 6 (not 38) by my count. Those 6 are all for direct IO
>>> (see below) which is off by default. I suspect old scanning
>>> utilities like sg_scan and sg_map might also use /proc/scsi/* .
>>> That is one reason why I wrote lsscsi. However I can't force folks
>>> to use lsscsi. As a related example, I still get bug reports for
>>> sginfo which I inherited from Eric Youngdale.
>>>
>>> If I was asked to debug a problem with the sg driver in a
>>> system without CONFIG_SCSI_PROC_FS defined, I would decline.
>>>
>>> The absence of /proc/scsi/sg/debug would be my issue. Can this
>>> be set up to do the same thing:
>>>      cat /sys/class/scsi_generic/debug
>>>    Is that breaking any sysfs rules?
>>>
>>>
>>> Also folks who rely on this to work:
>>>     cat /proc/scsi/sg/devices
>>> 0	0	0	0	0	1	255	0	1
>>> 0	0	0	1	0	1	255	0	1
>>> 0	0	0	2	0	1	255	0	1
>>>
>>> would be disappointed. Further I note that setting allow_dio via
>>> /proc/scsi/sg/allow_dio can also be done via /sys/module/sg/allow_dio .
>>> So that would be an interface breakage, but with an alternative.
>>
>> You can grep for /proc/scsi/ across all Debian packages:
>> https://codesearch.debian.net/
>>
>> This reveals that /proc/scsi/sg/ appears in smartmontools and other
>> packages, for example.
> 
> Hello everyone,
> 
> Please note that I am _in no way_ suggesting that we remove any code.
> 
> I just think it might be time to stop forcing CONFIG_SCSI_PROC_FS into
> every config, and instead require one to explicitly request the aging
> feature (which makes CONFIG_SCSI_PROC_FS show up in a defconfig).
> 
> Maybe we could add CONFIG_SCSI_PROC_FS to arch/x86/configs/foo ?
> (For which foo? In a separate patch or squashed with this one?)

Marc,
Since current sg driver usage seems to depend more on SCSI_PROC_FS
being "y" than other parts of the SCSI subsystem then if
SCSI_PROC_FS is to default to "n" in the future then a new
CONFIG_SG_PROC_FS variable could be added.

If CONFIG_CHR_DEV_SG is "*" or "m" then default CONFIG_SG_PROC_FS
to "y"; if CONFIG_SCSI_PROC_FS is "y" then default CONFIG_SG_PROC_FS
to "y"; else default CONFIG_SG_PROC_FS to "n". Obviously the
sg driver would need to be changed to use CONFIG_SG_PROC_FS instead
of CONFIG_SCSI_PROC_FS .


Does that defeat the whole purpose of your proposal or could it be
seen as a partial step in that direction? What is the motivation
for this proposal?

Doug Gilbert


BTW We still have the non-sg related 'cat /proc/scsi/scsi' usage
and 'cat /proc/scsi/device_info'. And I believe the latter one is
writable even though its permissions say otherwise.

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