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. >
May be it's better to use monitor_fd_param for both incoming/outgoing? So, "migrate" will know fd:<int> semantics and "migrate-incoming" will know fd:<fd_name> semantics. And also modify monitor_get_fd to remove fd from list before return. This is a backwards compatible change. Regards, Yury
