On Wed, 13 Jun 2012 18:07:43 -0400 Corey Bryant <coreyb@linux.vnet.ibm.com> wrote:
On 06/13/2012 04:47 PM, Eric Blake wrote:
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'.
Yes, users need to be careful and understand how the commands work. I don't think it's a hard rule that 'getfd' can't be used by an application that uses 'pass-fd'. If it were, we could put the fds on separate lists:
struct Monitor { ... QLIST_HEAD(,mon_fd_t) fds; + QLIST_HEAD(,mon_fd_t) pass_fds; };
We'd a different closefd command if we do this.
But I don't think this is necessary, so I'll plan on documenting them well.
Agreed, I don't think this is necessary.