Re: [libvirt] [PATCH v2 6/7] domain_lock: Implement metadata locking

On 08/20/2018 05:07 PM, Daniel P. Berrangé wrote: > On Tue, Aug 14, 2018 at 01:19:42PM +0200, Michal Privoznik wrote: >> In order for our drivers to lock resources for metadata change we >> need set of new APIs. Fortunately, we don't have to care about >> every possible device a domain can have. We care only about those >> which can live on a network filesystem and hence can be accessed >> by multiple daemons at the same time. These devices are covered >> in virDomainLockMetadataLock() and only a small fraction of >> those can be hotplugged (covered in the rest of the introduced >> APIs). > > I'm not sure I understand the rationale behind saying we only care > about resources on network filesystems. > > If I have 2 locally running guests, and both have a serial port > backed by a physical serial port, eg > > <serial type="dev"> > <source path="/dev/ttyS0"/> > <target port="1"/> > </serial> > > we *do* care about locking /dev/ttyS0, as libvirtd isn't doing > mutual exclusion checks anywhere else for the /dev/ttyS0 device > node. Ah you mean that the system wide daemon and session daemon could clash when relabeling /dev/ttyS0? Well, we don't do relabeling for session daemons and running two system daemons is not supported (you're gonna hit more serious problems when trying that anyway).