On Thu, Apr 23, 2020 at 2:48 AM Josh Triplett <josh@xxxxxxxxxxxxxxxx> wrote: > > On Wed, Apr 22, 2020 at 09:55:56AM +0200, Miklos Szeredi wrote: > > On Wed, Apr 22, 2020 at 8:06 AM Michael Kerrisk (man-pages) > > <mtk.manpages@xxxxxxxxx> wrote: > > > > > > [CC += linux-api] > > > > > > On Wed, 22 Apr 2020 at 07:20, Josh Triplett <josh@xxxxxxxxxxxxxxxx> wrote: > > > > > > > > Inspired by the X protocol's handling of XIDs, allow userspace to select > > > > the file descriptor opened by openat2, so that it can use the resulting > > > > file descriptor in subsequent system calls without waiting for the > > > > response to openat2. > > > > > > > > In io_uring, this allows sequences like openat2/read/close without > > > > waiting for the openat2 to complete. Multiple such sequences can > > > > overlap, as long as each uses a distinct file descriptor. > > > > If this is primarily an io_uring feature, then why burden the normal > > openat2 API with this? > > This feature was inspired by io_uring; it isn't exclusively of value > with io_uring. (And io_uring doesn't normally change the semantics of > syscalls.) What's the use case of O_SPECIFIC_FD beyond io_uring? > > > This would also allow Implementing a private fd table for io_uring. > > I.e. add a flag interpreted by file ops (IORING_PRIVATE_FD), including > > openat2 and freely use the private fd space without having to worry > > about interactions with other parts of the system. > > I definitely don't want to add a special kind of file descriptor that > doesn't work in normal syscalls taking file descriptors. A file > descriptor allocated via O_SPECIFIC_FD is an entirely normal file > descriptor, and works anywhere a file descriptor normally works. What's the use case of allocating a file descriptor within io_uring and using it outside of io_uring? Thanks, Miklos
