On 06/13/2012 02:25 PM, Corey Bryant wrote:
Also, getfd automatically closes a fd if an existing fdname is passed again. I don't think this is a good behavior, I think pass-fd should fail instead (note that we can't fix getfd though).
I agree. It makes sense to fail rather than blindly closing the existing fd. It can be closed explicitly with closefd if the user wants it closed.
Hmm - what happens if I do 'pass-fd name', learn that qemu is using fd 42, then do 'getfd name'? I silently wipe out fd 42 and replace it with the new fd passed in by getfd. Which means my use of /dev/fd/42 will now be broken. Obviously that means that 'getfd' should NOT be used by any application using 'pass-fd', and that libvirt should NOT be reusing names (I think the latter is already true). But I agree that for back-compat we can't get rid of the current (evil) semantics of a duplicated 'getfd'. You may also want to mention that when using 'getfd' or 'pass-fd', there are some commands (like migrate) that use the fd:name protocol, and that a successful use of one of these commands implicitly closes the named fd; but that all new uses of /dev/fd/nnn leave the fd open and an explicit closefd must be used to avoid leaking indefinitely-opened fds in qemu. -- Eric Blake eblake@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org