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Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol


From: Yury Kotov
Subject: Re: [Qemu-devel] [PATCH] migration: Fix handling fd protocol
Date: Mon, 15 Apr 2019 13:24:24 +0300

15.04.2019, 13:17, "Yury Kotov" <address@hidden>:
> 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.
>>

But qemu_close is already deal with monitor:
It uses monitor_fdset_dup_fd_find & monitor_fdset_dup_fd_remove to find and
remove fd from monitor's dup_fds list.

>>>   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.
>

Regards,
Yury



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