Messages in this thread | | | From | Suren Baghdasaryan <> | Date | Mon, 3 Aug 2020 19:10:59 -0700 | Subject | Re: [PATCH 2/2] dmabuf/tracing: Add dma-buf trace events |
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On Mon, Aug 3, 2020 at 6:09 PM Al Viro <viro@zeniv.linux.org.uk> 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.
Thanks for your feedback, Al. I see your points and sorry for not realizing these shortcomings.
> > > > You are looking at the drastically wrong abstraction level. Please, describe what > > it is that you are trying to achieve. > > _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.
That is the intention here. IIUC fuser(1) would require root access to collect this information from a process other than the caller. Ideally what we would like to have is a non-root process with specific capabilities (in our case a process that can access BPF maps) to be able to obtain the information on dma-buf users. However, it might make more sense to track dma-buf usage from dma_buf_getfile, dma_buf_get and dma_buf_put since these calls are the ones that affect file refcount. Will dig some more into this. Thanks for your time and sorry for not thinking it through beforehand.
> > But that's only a semi-blind guess at the things you are trying to achieve; please, > describe what it really is.
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