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Date:   Tue, 18 Jun 2019 11:08:03 +1000 (AEST)
From:   Finn Thain <fthain@telegraphics.com.au>
To:     Douglas Gilbert <dgilbert@interlog.com>
cc:     Bart Van Assche <bvanassche@acm.org>,
        Marc Gonzalez <marc.w.gonzalez@free.fr>,
        James Bottomley <jejb@linux.ibm.com>,
        Martin Petersen <martin.petersen@oracle.com>,
        SCSI <linux-scsi@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v1] scsi: Don't select SCSI_PROC_FS by default
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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 superseded for ~15 years.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@free.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  In Linux 2.6 this has been superseded by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
> 

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.

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