[libvirt] [PATCH 00/11] Avoid numerous calls of virQEMUCapsCacheLookup

[Bjoern Walk]

Daniel P. Berrangé <berrange at redhat.com> [2018-10-25, 06:32PM +0100]:
> On Thu, Oct 25, 2018 at 01:47:26PM +0200, Bjoern Walk wrote:
> > Daniel P. Berrangé <berrange at redhat.com> [2018-10-24, 10:43PM +0100]:
> > > We could optimize this by jcalling virFileAccessibleAs
> > > once and storing the result in a global. Then just do a
> > > plain stat() call in process to check the st_ctime field
> > > for changes. We only need re-run the heavy virFileAccessibleAs
> > > check if st_ctime has changed (indicating a owner/group/acl
> > > change).
> > 
> > But can't access permission change outside of changing the actual device
> > file (e.g. cgroups or other OS capabilities)? Isn't that the whole
> > purpose of the virFileAccessibleAs gymnastics?
> 
> Yes, cgroups could restrict access to /dev/kvm, but virFileAccessibleAs
> does not use cgroups, it only cares about using the correct user + group
> membership. 

Sorry, but then I don't understand the purpose of this function at all.
Why would you EVER check permissions like that? A simple stat(2) call
should give you the exact same information, no?

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