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Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol |
Date: |
Mon, 15 Apr 2019 12:15:12 +0100 |
User-agent: |
Mutt/1.11.4 (2019-03-13) |
* Daniel P. Berrangé (address@hidden) wrote:
> On Mon, Apr 15, 2019 at 01:33:21PM +0300, Yury Kotov wrote:
> > 15.04.2019, 13:25, "Daniel P. Berrangé" <address@hidden>:
> > > On Mon, Apr 15, 2019 at 01:17:06PM +0300, Yury Kotov wrote:
> > >> 15.04.2019, 13:11, "Daniel P. Berrangé" <address@hidden>:
> > >> > On Mon, Apr 15, 2019 at 12:50:08PM +0300, Yury Kotov wrote:
> > >> >> Hi,
> > >> >>
> > >> >> Just to clarify. I see two possible solutions:
> > >> >>
> > >> >> 1) Since the migration code doesn't receive fd, it isn't
> > >> responsible for
> > >> >> closing it. So, it may be better to use migrate_fd_param for both
> > >> >> incoming/outgoing and add dupping for migrate_fd_param. Thus,
> > >> clients must
> > >> >> close the fd themselves. But existing clients will have a leak.
> > >> >
> > >> > We can't break existing clients in this way as they are correctly
> > >> > using the monitor with its current semantics.
> > >> >
> > >> >> 2) If we don't duplicate fd, then at least we should remove fd from
> > >> >> the corresponding list. Therefore, the solution is to fix
> > >> qemu_close to find
> > >> >> the list and remove fd from it. But qemu_close is currently
> > >> consistent with
> > >> >> qemu_open (which opens/dups fd), so adding additional logic might
> > >> not be
> > >> >> a very good idea.
> > >> >
> > >> > qemu_close is not appropriate place to deal with something speciifc
> > >> > to the montor.
> > >> >
> > >> >> I don't see any other solution, but I might miss something.
> > >> >> What do you think?
> > >> >
> > >> > All callers of monitor_get_fd() will close() the FD they get back.
> > >> > Thus monitor_get_fd() should remove it from the list when it returns
> > >> > it, and we should add API docs to monitor_get_fd() to explain this.
> > >> >
> > >> Ok, it sounds reasonable. But monitor_get_fd is only about outgoing
> > >> migration.
> > >> But what about the incoming migration? It doesn't use monitor_get_fd
> > >> but just
> > >> converts input string to int and use it as fd.
> > >
> > > The incoming migration expects the FD to be passed into QEMU by the mgmt
> > > app when it is exec'ing the QEMU binary. It doesn't interact with the
> > > monitor at all AFAIR.
> > >
> >
> > Oh, sorry. This use case is not obvious. We used add-fd to pass fd for
> > migrate-incoming and such way has described problems.
>
> That's a bug in your usage of QEMU IMHO, as the incoming code is not
> designed to use add-fd.
Hmm, that's true - although:
a) It's very non-obvious
b) Unfortunate, since it would go well with -incoming defer
Dave
> Regards,
> Daniel
> --
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--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, (continued)
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Yury Kotov, 2019/04/11
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Daniel P . Berrangé, 2019/04/11
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Yury Kotov, 2019/04/11
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Yury Kotov, 2019/04/15
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Daniel P . Berrangé, 2019/04/15
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Yury Kotov, 2019/04/15
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Yury Kotov, 2019/04/15
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Daniel P . Berrangé, 2019/04/15
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Yury Kotov, 2019/04/15
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Daniel P . Berrangé, 2019/04/15
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol,
Dr. David Alan Gilbert <=
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Daniel P . Berrangé, 2019/04/15
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Dr. David Alan Gilbert, 2019/04/15
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Yury Kotov, 2019/04/15
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Yury Kotov, 2019/04/16
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Yury Kotov, 2019/04/16
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Dr. David Alan Gilbert, 2019/04/18
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Yury Kotov, 2019/04/18
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Dr. David Alan Gilbert, 2019/04/18
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Yury Kotov, 2019/04/18
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Dr. David Alan Gilbert, 2019/04/18