linux-kernel - Re: [PATCH v3 5/6] blktrace: break out of blktrace setup on concurrent calls

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Date:   Fri, 1 May 2020 09:50:17 -0600
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>,
        Christof Schmitt <christof.schmitt@...ibm.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, Jens Axboe <axboe@...nel.dk>,
        Al Viro <viro@...iv.linux.org.uk>,
        Bart Van Assche <bvanassche@....org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, Jan Kara <jack@...e.cz>,
        Ming Lei <ming.lei@...hat.com>,
        Nicolai Stange <nstange@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, yu kuai <yukuai3@...wei.com>,
        linux-block@...r.kernel.org,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 5/6] blktrace: break out of blktrace setup on
 concurrent calls

On Fri, May 1, 2020 at 9:40 AM Luis Chamberlain <mcgrof@...nel.org> wrote:
>
> On Fri, May 01, 2020 at 08:34:23AM -0700, Christoph Hellwig wrote:
> > On Fri, May 01, 2020 at 03:06:26PM +0000, Luis Chamberlain wrote:
> > > > You have access to a block device here, please use dev_warn() instead
> > > > here for that, that makes it obvious as to what device a "concurrent
> > > > blktrace" was attempted for.
> > >
> > > The block device may be empty, one example is for scsi-generic, but I'll
> > > use buts->name.
> >
> > Is blktrace on /dev/sg something we intentionally support, or just by
> > some accident of history?  Given all the pains it causes I'd be tempted
> > to just remove the support and see if anyone screams.
>
> From what I can tell I think it was a historic and brutal mistake. I am
> more than happy to remove it.

I take that back:

commit 6da127ad0918f93ea93678dad62ce15ffed18797
Author: Christof Schmitt <christof.schmitt@...ibm.com>
Date:   Fri Jan 11 10:09:43 2008 +0100

    blktrace: Add blktrace ioctls to SCSI generic devices

    Since the SCSI layer uses the request queues from the block layer,
blktrace can
    also be used to trace the requests to all SCSI devices (like SCSI
tape drives),
    not only disks. The only missing part is the ioctl interface to
start and stop
    tracing.

    This patch adds the SETUP, START, STOP and TEARDOWN ioctls from
blktrace to the
    sg device files. With this change, blktrace can be used for SCSI
devices like
    for disks, e.g.: blktrace -d /dev/sg1 -o - | blkparse -i -

    Signed-off-by: Christof Schmitt <christof.schmitt@...ibm.com>
    Signed-off-by: Jens Axboe <jens.axboe@...cle.com>

Christof, any thoughts on removing this support?

 Luis