Re: [libvirt] [Qemu-devel] [PATCH v2 3/3] qemu-config: Add new -add-fd command line option

On 10/11/2012 08:45 AM, Corey Bryant wrote: >> Another missing validation check is for duplicate use. With the monitor >> command, you ALWAYS have a unique fd (thanks to SCM_RIGHTS). But with >> the command line, I can type 'qemu -add-fd fd=4,set=1 -add-fd >> fd=4,set=2'. Oops - I've now corrupted your set layout, unless you >> validate that every fd requested in -add-fd does not already reside in >> any existing set. >> > > I don't see this validation check for duplicate use of fd's being > necessary. Like you say below, in the QMP add-fd case we can add the > same fd multiple times. So we should be able to add the same fd > multiple times via the command line. The only difference between QMP > and command line in this case is that the QMP fd is a dup and therefore > a different number and the command line fd will be the same fd. I'd > prefer to leave this alone unless there's a compelling reason to block > adding of the same fd. There is a compelling reason to prevent duplicates among your sets: qemu_close(). Suppose I add fd 4 into set 1 and 2, and then discard set 2 via monitor commands. Then, when qemu_close() drops the last reference to set 2, it steps through and calls close() on all fds in that set, including fd 4. Oops - now set 1 is invalid, because it is tracking a closed fd. And worse, if qemu then does something else to open a new fd, it will get fd 4 again, and now set 1 will be tracking the WRONG fd.