On 25/10/2019 19:05, Anthony PERARD wrote: > Patch series available in this git branch: > https://xenbits.xen.org/git-http/people/aperard/xen-unstable.git > br.fix-ev_qmp-multi-connect-v1 > > Hi, > > QEMU's QMP socket doesn't allow multiple concurrent connection. Also, it > listen() on the socket with a `backlog' of only 1. On Linux at least, once > that > backlog is filled connect() will return EAGAIN if the socket fd is > non-blocking. libxl may attempt many concurrent connect() attempt if for > example a guest is started with several PCI passthrough devices, and a > connect() failure lead to a failure to start the guest.
Hi Anthony, Just tested with the patch series and it fixes my issue with starting a guest with several PCI passthrough devices. Thanks, Sander > Since we can't change the listen()'s `backlog' that QEMU use, we need other > ways to workaround the issue. This patch series introduce a lock to acquire > before attempting to connect() to the QMP socket. Since the lock might be held > for to long, the series also introduce a way to cancel the acquisition of the > lock, this means killing the process that tries to get the lock. > > Alternatively to this craziness, it might be possible to increase the > `backlog' > value by having libxl opening the QMP socket on behalf of QEMU. But this is > only possible with a recent version of QEMU (2.12 or newer, released in Apr > 2018, or qemu-xen-4.12 or newer). It would involve to discover QEMU's > capability before we start the DM, which libxl isn't capable yet. > > Cheers, > > Anthony PERARD (4): > libxl: Introduce libxl__ev_child_kill > libxl: Introduce libxl__ev_qmplock > libxl: libxl__ev_qmp_send now takes an egc > libxl_qmp: Have a lock for QMP socket access > > tools/libxl/libxl_disk.c | 6 +-- > tools/libxl/libxl_dm.c | 8 ++-- > tools/libxl/libxl_dom_save.c | 2 +- > tools/libxl/libxl_dom_suspend.c | 2 +- > tools/libxl/libxl_domain.c | 8 ++-- > tools/libxl/libxl_event.c | 3 +- > tools/libxl/libxl_fork.c | 55 ++++++++++++++++++++++++ > tools/libxl/libxl_internal.c | 31 +++++++++++++- > tools/libxl/libxl_internal.h | 53 +++++++++++++++++------ > tools/libxl/libxl_pci.c | 8 ++-- > tools/libxl/libxl_qmp.c | 75 +++++++++++++++++++++++++-------- > tools/libxl/libxl_usb.c | 28 ++++++------ > 12 files changed, 219 insertions(+), 60 deletions(-) > -- Met vriendelijke groet, Sander Eikelenboom mailto:san...@eikelenboom.it Eikelenboom IT Services Kaapseweg 70 5642 HK Eindhoven M: 06-14387484 PGP public key for san...@eikelenboom.it: key id: 0xC4B99EEDECF2AE69 fingerprint: 07BB B819 FF93 E54D 5F5C 0BDE C4B9 9EED ECF2 AE69 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
