On Thu, Jun 21, 2018 at 2:34 PM Christoph Hellwig [off-list ref] wrote:

On Mon, Jun 18, 2018 at 09:37:01AM -0600, Jens Axboe wrote:

quoted

It was born with that mode, but I don't think anyone ever really used it.
So it might feasible to simply yank it. That said, just doing a prune
mode at ->release() time doesn't seem like such a hard task.

Let's try to kill it.  It is a significant amount of code, which does
fishy things and is probably entirely unused:

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From baec733be1b400d73d0fa2bfc07684598c4172e7 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Thu, 21 Jun 2018 14:31:32 +0200
Subject: bsg: remove read/write support

The code poses a security risk due to user memory access in ->release
and had an API that can't be used reliably.  As far as we know it was
never used for real, but if that turns out wrong we'll have to revert
this commit and come up with a band aid.

FWIW, I just had a look through Debian's codesearch (which AFAIK scans
through the source code of all software that Debian packages) for uses
of struct sg_io_v4: https://codesearch.debian.net/search?q=sg_io_v4

Hits that seem to be using read() or write() with struct sg_io_v4 on
bsg devices:

In the package https://packages.debian.org/stretch/tgt:
  https://sources.debian.org/src/tgt/1:1.0.73-1/usr/bs_sg.c/?hl=131#L131
  https://sources.debian.org/src/tgt/1:1.0.73-1/usr/bs_sg.c/?hl=236#L236
In the package https://packages.debian.org/stretch/sg3-utils:
  https://sources.debian.org/src/sg3-utils/1.42-2/examples/bsg_queue_tst.c/?hl=60#L60