On 06/04/2013 01:24 PM, Markus Armbruster wrote: > Paolo Bonzini <pbonz...@redhat.com> writes: > >> Il 04/06/2013 18:37, Markus Armbruster ha scritto: >>> I figure the bit that can't be resolved now is letting the user switch >>> off "stop on error" safely before a drive_del. Even if we had a command >>> for that, there'd still be a window between that command's execution and >>> drive_del's. Your patch solves the problem by having drive_del switch >>> it off unconditionally. Oookay, but please document it, because it's >>> not exactly obvious. >> >> It is not obvious, but it is not surprising either when you see it (i.e. >> you won't really be surprised by the errors in the guest and won't need >> to know that, under the hood, rerror has been changed from the value you >> specified). >>
> This is drive_add's documentation in hmp-commands.hx: > > Remove host block device. The result is that guest generated IO is > no longer submitted against the host device underlying the disk. > Once a drive has been deleted, the QEMU Block layer returns -EIO > which results in IO errors in the guest for applications that are > reading/writing to the device. > > Suggest to add: > > These errors are always reported to the guest, regardless of the > drive's error actions (drive options rerror, werror). > > Independently, libvirt needs fixing. Total agreement that libvirt needs to use a saner disk hot-unplug sequence when it is known that qemu provides one. I've filed https://bugzilla.redhat.com/show_bug.cgi?id=970761 to remind us to fix libvirt. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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