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

Demi Marie Obenour
2023-02-02T18:43:55Z

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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@invisiblethingslab.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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