linux-kernel - Re: [PATCH 3/3] block: add back command filter modification via sysfs

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Date:   Fri, 16 Nov 2018 06:42:45 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-scsi@...r.kernel.org, Hannes Reinecke <hare@...e.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>
Subject: Re: [PATCH 3/3] block: add back command filter modification via
 sysfs

On Fri, 2018-11-16 at 08:00 +0100, Paolo Bonzini wrote:
> On 16/11/18 06:46, Bart Van Assche wrote:
> > I do not know any application for which it would be useful to allow some but
> > not all of these commands. With the proposed interface however users will
> > have to examine all SCSI opcodes and for each opcode they will have to decide
> > whether or not it should be allowed. Additionally, for opcodes like 7fh that
> > represent multiple commands, users will have to decide whether they want to
> > allow all these commands or none. That's why I think that filtering SCSI
> > commands based on their CDB is an unfortunate choice. Would it be sufficient
> > for the use cases you are looking at to group SCSI commands as follows and to
> > enable/disable these commands per group:
> > * SCSI command that read information from the medium (e.g. READ) or from the
> >   controller (e.g. READ CAPACITY).
> > * SCSI commands that modify information on the medium (e.g. WRITE).
> > * SCSI commands that modify controller settings (e.g. MODE SELECT or SET
> >   TARGET PORT GROUPS).
> 
> And also:
> 
> * all SCSI commands (e.g. write microcode, vendor specific commands).
> 
> It would.  However, it would be impossible to do this without making the
> filter depend on the SCSI device type.  This has been rejected in 2012.

Do you have a link available to that discussion? Since the meaning of several
SCSI opcodes depends on the SCSI device type, I don't see how we can avoid
making filtering dependent on the SCSI device type.

Bart.