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

From: Douglas Gilbert
Date: Tue Jun 18 2019 - 11:37:00 EST

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superseded for ~15 years.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
bool "legacy /proc/scsi/ support"
depends on SCSI && PROC_FS
- default y
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 In Linux 2.6 this has been superseded by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

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";
static const char * proc_allow_dio = "/proc/scsi/sg/allow_dio";
static const char * proc_allow_dio = "/proc/scsi/sg/allow_dio";
static const char * proc_allow_dio = "/proc/scsi/sg/allow_dio";
"'echo 1 > /proc/scsi/sg/allow_dio'\n", q_len, dirio_count);
static const char * proc_allow_dio = "/proc/scsi/sg/allow_dio";

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:

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?)

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

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.