linux-kernel - Re: [PATCH v1] scsi: Don't select SCSI_PROC

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Message-ID: <fb2d2e74-6725-4bf2-cf6c-63c0a2a10f4f@interlog.com>
Date:   Mon, 17 Jun 2019 20:35:50 -0400
From:   Douglas Gilbert <dgilbert@...erlog.com>
To:     Bart Van Assche <bvanassche@....org>,
        Marc Gonzalez <marc.w.gonzalez@...e.fr>,
        James Bottomley <jejb@...ux.ibm.com>,
        Martin Petersen <martin.petersen@...cle.com>
Cc:     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 2019-06-17 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 superseded for ~15 years.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  In Linux 2.6 this has been superseded by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.

Doug Gilbert