On Tue, Aug 04, 2020 at 02:09:13AM +0100, Al Viro wrote: > On Mon, Aug 03, 2020 at 11:28:31PM +0100, Al Viro wrote: > > > IOW, what the hell is that horror for? You do realize, for example, that > > there's > > such thing as dup(), right? And dup2() as well. And while we are at it, > > how > > do you keep track of removals, considering the fact that you can stick a > > file > > reference into SCM_RIGHTS datagram sent to yourself, close descriptors and > > an hour > > later pick that datagram, suddenly getting descriptor back? > > > > Besides, "I have no descriptors left" != "I can't be currently sitting in > > the middle > > of syscall on that sucker"; close() does *NOT* terminate ongoing operations. > > > > You are looking at the drastically wrong abstraction level. Please, > > describe what > > it is that you are trying to achieve.
Hi Al. Thank you for the comments. Ultimately what we need is to identify processes that hold a file reference to the dma-buf. Unfortunately we can't use only explicit dma_buf_get/dma_buf_put to track them because when an FD is being shared between processes the file references are taken implicitly. For example, on the sender side: unix_dgram_sendmsg -> send_scm -> __send_scm -> scm_fp_copy -> fget_raw and on the receiver side: unix_dgram_recvmsg -> scm_recv -> scm_detach_fds -> __scm_install_fd -> get_file I understand now that fd_install is not an appropriate abstraction level to track these. Is there a more appropriate alternative where we could use to track these implicit file references? > _IF_ it's "who keeps a particularly long-lived sucker pinned", I would suggest > fuser(1) run when you detect that kind of long-lived dmabuf. With events > generated > by their constructors and destructors, and detection of longevity done based > on > that. > > But that's only a semi-blind guess at the things you are trying to achieve; > please, > describe what it really is.
