From: Ian Jackson <iwj@xenproject.org>
To: Manuel Bouyer <bouyer@antioche.eu.org>
Cc: "Roger Pau Monné" <roger.pau@citrix.com>, xen-devel@lists.xenproject.org
Subject: Re: [PATCH 05/24] Introduce locking functions for block device setup on NetBSD
Date: Wed, 20 Jan 2021 15:13:22 +0000 [thread overview]
Message-ID: <24584.18578.623201.789017@mariner.uk.xensource.com> (raw)
In-Reply-To: <20210104102037.GA2005@antioche.eu.org>
Manuel Bouyer writes ("Re: [PATCH 05/24] Introduce locking functions for block device setup on NetBSD"):
> On Tue, Dec 29, 2020 at 12:29:09PM +0100, Roger Pau Monné wrote:
> > I think you want tot CC the tools dev on this one, specially Ian who
> > knows how the Linux one is implemented and can likely give valuable
> > input.
...
> > Seeing the file itself, I don't think there's any NetBSD specific
> > stuff, so we might want to consider putting it in BSD/ instead, so it
> > can be used by FreeBSD also?
>
> I'm not sure if FreeBSD needs the locking stuff.
> Also, there are certainly differences in block device handling between
> FreeBSD and NetBSD. Both OSes have diverged in this area.
I think most operating systems will want some kind of locking here.
I loooked at the code in the new tools/hotplug/NetBSD/locking.sh.
Unfortunately this area is complex and the available APIs and tools
are awkard, and the field is troubled by broken "traditional"
approaches involving O_EXCL or the moral equivalent, which cannot be
made reliable (if you think reliability implies never being broken due
to stale lock).
I doubt that the code in this patch is correct. It uses shlock(1)
which is based on link(2) and kill(2) and so on, which I think is
basically an O_EXCL-based approach as I discuss above. (I don't have
a formal proof of this contention.) The presence of an invocation of
the "trap" shell builtin in the new NetBSD script is a bad sign - a
reliable locking protocol would need that.
I see from https://man.netbsd.org that NetBSD has flock(1) and
stat(1). I think this means we could reuse the code in
tools/hotplug/Linux/locking.sh. Maybe it will need to be lightly
adapted, to NetBSD's flock(1) and stat(1). Perhaps via some kind of
substitution to avoid all the clone-and-hack.
Regards,
Ian.
next prev parent reply other threads:[~2021-01-20 15:13 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-14 16:35 [PATCH 00/24] NetBSD fixes Manuel Bouyer
2020-12-14 16:36 ` [PATCH 01/24] Fix lock directory path for NetBSD Manuel Bouyer
2020-12-14 16:36 ` [PATCH 02/24] NetBSD doens't need xenbackendd with xl toolstack Manuel Bouyer
2020-12-29 11:17 ` Roger Pau Monné
2020-12-14 16:36 ` [PATCH 03/24] Fix lock directory path for NetBSD Manuel Bouyer
2020-12-14 16:36 ` [PATCH 04/24] Make xg_main.c build on NetBSD Manuel Bouyer
2020-12-29 11:24 ` Roger Pau Monné
2020-12-14 16:36 ` [PATCH 05/24] Introduce locking functions for block device setup " Manuel Bouyer
2020-12-29 11:29 ` Roger Pau Monné
2021-01-04 10:20 ` Manuel Bouyer
2021-01-20 15:13 ` Ian Jackson [this message]
2021-01-20 15:59 ` Manuel Bouyer
2021-01-20 16:12 ` Ian Jackson
2021-01-20 16:59 ` Manuel Bouyer
2021-01-20 17:03 ` Ian Jackson
2021-01-20 17:19 ` Ian Jackson
2020-12-14 16:36 ` [PATCH 06/24] Handle the case where vifname is not present in xenstore Manuel Bouyer
2020-12-29 11:43 ` Roger Pau Monné
2021-01-04 10:22 ` Manuel Bouyer
2020-12-14 16:36 ` [PATCH 07/24] Remove NetBSD's system headers. We'll use the system-provided ones, which are up to date Manuel Bouyer
2020-12-29 11:46 ` Roger Pau Monné
2021-01-04 10:25 ` Manuel Bouyer
2021-01-04 17:09 ` Roger Pau Monné
2021-01-04 17:20 ` Manuel Bouyer
2020-12-14 16:36 ` [PATCH 08/24] Make libs/call build on NetBSD Manuel Bouyer
2020-12-29 11:49 ` Roger Pau Monné
2020-12-14 16:36 ` [PATCH 09/24] Use xen/xenio.h " Manuel Bouyer
2020-12-14 16:36 ` [PATCH 10/24] Make libs/evtchn build " Manuel Bouyer
2020-12-29 11:52 ` Roger Pau Monné
2021-01-04 10:26 ` Manuel Bouyer
2021-01-04 17:15 ` Roger Pau Monné
2021-01-10 12:22 ` Manuel Bouyer
2021-01-11 17:22 ` Roger Pau Monné
2020-12-14 16:36 ` [PATCH 11/24] Implement foreignmemory " Manuel Bouyer
2020-12-29 12:46 ` Roger Pau Monné
2021-01-04 11:30 ` Manuel Bouyer
2021-01-04 18:24 ` Roger Pau Monné
2020-12-14 16:36 ` [PATCH 12/24] Implement gnttab " Manuel Bouyer
2020-12-29 11:16 ` Roger Pau Monné
2021-01-04 10:29 ` Manuel Bouyer
2021-01-04 17:24 ` Roger Pau Monné
2021-01-10 12:40 ` Manuel Bouyer
2021-01-11 17:04 ` Roger Pau Monné
2020-12-14 16:36 ` [PATCH 13/24] Don't assume tv_sec is a unsigned long (for NetBSD) Manuel Bouyer
2020-12-29 14:02 ` Roger Pau Monné
2021-01-04 10:31 ` Manuel Bouyer
2021-01-04 18:17 ` Roger Pau Monné
2020-12-14 16:36 ` [PATCH 14/24] Pass bridge name to qemu and set XEN_DOMAIN_ID Manuel Bouyer
2020-12-15 8:44 ` Manuel Bouyer
2020-12-29 15:19 ` Roger Pau Monné
2021-01-04 10:36 ` Manuel Bouyer
2020-12-14 16:36 ` [PATCH 15/24] Make libs/light build on NetBSD Manuel Bouyer
2020-12-29 14:15 ` Roger Pau Monné
2020-12-14 16:36 ` [PATCH 16/24] Switch NetBSD to QEMU_XEN (!traditional) Manuel Bouyer
2020-12-29 14:19 ` Roger Pau Monné
2021-01-04 10:47 ` Manuel Bouyer
2020-12-14 16:36 ` [PATCH 17/24] Make libs/light build on NetBSD Manuel Bouyer
2020-12-29 14:28 ` Roger Pau Monné
2020-12-14 16:36 ` [PATCH 18/24] xeneventchn_stubs.c doens't need xen/sys/evtchn.h (NetBSD fix) Manuel Bouyer
2020-12-29 14:30 ` Roger Pau Monné
2020-12-14 16:36 ` [PATCH 19/24] errno may not be a gobal R/W variable, use a local variable instead (fix build on NetBSD) Manuel Bouyer
2020-12-29 14:38 ` Roger Pau Monné
2021-01-04 10:56 ` Manuel Bouyer
2021-01-04 13:30 ` Manuel Bouyer
2020-12-14 16:36 ` [PATCH 20/24] If FILENAME_MAX is defined, use it instead of arbitrary value (fix format-truncation errors with GCC >= 7) Manuel Bouyer
2020-12-29 14:51 ` Roger Pau Monné
2021-01-04 11:03 ` Manuel Bouyer
2020-12-14 16:36 ` [PATCH 21/24] Fix unused functions/variables error Manuel Bouyer
2020-12-14 16:36 ` [PATCH 22/24] If PTHREAD_STACK_MIN is not defined, use DEFAULT_THREAD_STACKSIZE Manuel Bouyer
2020-12-29 14:57 ` Roger Pau Monné
2020-12-14 16:36 ` [PATCH 23/24] Use xen/xenio.h on NetBSD Manuel Bouyer
2020-12-14 16:36 ` [PATCH 24/24] Fix error: array subscript has type 'char' [-Werror=char-subscripts] Manuel Bouyer
2020-12-29 15:23 ` [PATCH 00/24] NetBSD fixes Roger Pau Monné
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