Re: [PATCH v1] scsi: Don't select SCSI_PROC_FS by default

[Douglas Gilbert]

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 superseded for ~15 years.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@xxxxxxx>
> > > > > ---
> > > > >    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  In Linux 2.6 this has been superseded by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.