* Yury Kotov (yury-ko...@yandex-team.ru) wrote: > 15.04.2019, 14:30, "Dr. David Alan Gilbert" <dgilb...@redhat.com>: > > * Daniel P. Berrangé (berra...@redhat.com) wrote: > >> On Mon, Apr 15, 2019 at 12:15:12PM +0100, Dr. David Alan Gilbert wrote: > >> > * Daniel P. Berrangé (berra...@redhat.com) wrote: > >> > > On Mon, Apr 15, 2019 at 01:33:21PM +0300, Yury Kotov wrote: > >> > > > 15.04.2019, 13:25, "Daniel P. Berrangé" <berra...@redhat.com>: > >> > > > > On Mon, Apr 15, 2019 at 01:17:06PM +0300, Yury Kotov wrote: > >> > > > >> 15.04.2019, 13:11, "Daniel P. Berrangé" <berra...@redhat.com>: > >> > > > >> > 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. > > > > Oh, I'm sorry again. I think my suggestion about monitor_fd_param wasn't > relevant to this issue. If migrate-incoming + "fd:" + add-fd is an invalid use > case, should we disallow this? > I may add a check to fd_start_incoming_migration if fd is in mon fds list. > But I'm afraid there are users like me who are already using this wrong use > case. > Because currently nothing in QEMU's docs disallow this. > > So which solution is better in your opinion? > 1) Disallow fd's from mon fds list in fd_start_incoming_migration
I'm surprised anything could be doing that - how would a user know what the correct fd index was? > 2) Allow these fds, but dup them or close them correctly I think I'd leave the current (confusing) fd: as it is, maybe put a note in the manual. > And how to migrate-incoming defer through fd correctly? > 1) Add "mon-fd:" protocol to work with fds passed by "add-fd/remove-fd" > commands > as suggested by Dave That's my preference; it's explicitly named and consistent, and it doesn't touch the existing fd code. Dave > 2) My suggestion about monitor_fd_param and make "fd:" for > migrate/migrate-incoming consistent. So user will be able to use > getfd + migrate-incoming > 3) Both of them or something else > > Regards, > Yury Kotov -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
