2017-09-07 Al Viro <viro@xxxxxxxxxxxxxxxxxx>: > On Thu, Sep 07, 2017 at 03:42:25PM -0300, Gustavo Padovan wrote: > > From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx> > > > > Rename __close_fd() to close_fd() and export it to be able close files > > in modules using file descriptors. > > > > The usecase that motivates this change happens in V4L2 where we send > > events to userspace with a fd that has file installed in it. But if for > > some reason we have to cancel the video stream we need to close the files > > that haven't been shared with userspace yet. Thus the export of > > close_fd() becomes necessary. > > > > fd_install() happens when we call an ioctl to queue a buffer, but we only > > share the fd with userspace later, and that may happen in a kernel thread > > instead. > > NAK. As soon as the reference is in descriptor table, you *can't* do anything > to it. This "sharing" part is complete BS - being _told_ that descriptor is > there does not matter at all. That descriptor might be hit with dup2() as > soon as fd_install() has happened. Or be closed, or any number of other things. > > You can not take it back. Once fd_install() is done, it's fucking done, period. > If V4L2 requires removing it from descriptor table, it's a shitty API and needs > to be fixed. Sorry for my lack of knowledge here and thank you for the explanation, things are a lot clear to me. For some reasons I were trying to delay the sharing of the fd to a event later. I can delay the install of it but that my require __fd_install() to be available and exportedi as it may happen in a thread, but I believe you wouldn't be okay with that either, is that so? Gustavo
