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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 12:30:46 +0100 |
User-agent: |
Mutt/1.11.4 (2019-03-13) |
* Daniel P. Berrangé (address@hidden) wrote:
> On Mon, Apr 15, 2019 at 12:15:12PM +0100, Dr. David Alan Gilbert wrote:
> > * 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
>
> Yeah I think this is a screw up on QMEU's part when introducing 'defer'.
>
> We should have mandated use of 'add-fd' when using 'defer', since FD
> inheritance-over-execve() should only be used for command line args,
> not monitor commands.
>
> Not sure how to best fix this is QEMU though without breaking back
> compat for apps using 'defer' already.
We could add mon-fd: transports that has the same behaviour as now for
outgoing, and for incoming uses the add-fd stash.
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, 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, 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, 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
- Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol, Yury Kotov, 2019/04/18