linux-kernel - Re: [RFC PATCH 0/7] Allow race-free block device handling

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Date:   Thu, 2 Feb 2023 13:41:29 -0500
From:   Demi Marie Obenour <demi@...isiblethingslab.com>
To:     Mike Snitzer <snitzer@...nel.org>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Roger Pau Monné <roger.pau@...rix.com>,
        Alasdair Kergon <agk@...hat.com>,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>, Juergen Gross <jgross@...e.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org, dm-devel@...hat.com
Subject: Re: [RFC PATCH 0/7] Allow race-free block device handling

On Thu, Feb 02, 2023 at 11:50:37AM -0500, Mike Snitzer wrote:
> On Wed, Jan 25 2023 at 10:33P -0500,
> Demi Marie Obenour <demi@...isiblethingslab.com> wrote:
> 
> > This work aims to allow userspace to create and destroy block devices
> > in a race-free and leak-free way,
> 
> "race-free and leak-free way" implies there both races and leaks in
> existing code. You're making claims that are likely very specific to
> your Xen use-case.  Please explain more carefully.

Will do in v2.

> > and to allow them to be exposed to
> > other Xen VMs via blkback without leaks or races.  It’s marked as RFC
> > for a few reasons:
> > 
> > - The code has been only lightly tested.  It might be unstable or
> >   insecure.
> > 
> > - The DM_DEV_CREATE ioctl gains a new flag.  Unknown flags were
> >   previously ignored, so this could theoretically break buggy userspace
> >   tools.
> 
> Not seeing a reason that type of DM change is needed. If you feel
> strongly about it send a separate patch and we can discuss it.

Patch 2/7 is the diskseq change.  v2 will contain a revised and tested
version with a greatly expanded commit message.

> > - I have no idea if I got the block device reference counting and
> >   locking correct.
> 
> Your headers and justifcation for this line of work are really way too
> terse. Please take the time to clearly make the case for your changes
> in both the patch headers and code.

I will expand the commit message in v2, but I am not sure what you want
me to add to the code comments.  Would you mind explaining?
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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