On Fri, 12 Feb 2021 at 13:14, Simon Ser <contact@xxxxxxxxxxx> wrote: > > On Friday, February 12th, 2021 at 1:57 PM, Emil Velikov <emil.l.velikov@xxxxxxxxx> wrote: > > > On Fri, 5 Feb 2021 at 22:01, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote: > > > > > > Userspace has discovered the functionality offered by SYS_kcmp and has > > > started to depend upon it. In particular, Mesa uses SYS_kcmp for > > > os_same_file_description() in order to identify when two fd (e.g. device > > > or dmabuf) > > > > As you rightfully point out, SYS_kcmp is a bit of a two edged sword. > > While you mention the CONFIG issue, there is also a portability aspect > > (mesa runs on more than just linux) and as well as sandbox filtering > > of the extra syscall. > > > > Last time I looked, the latter was still an issue and mesa was using > > SYS_kcmp to compare device node fds. > > A far shorter and more portable solution is possible, so let me > > prepare a Mesa patch. > > Comparing two DMA-BUFs can be done with their inode number, I think. > > Comparing two device FDs is more subtle, because of GEM handle > ref'counting. You sometimes really want to check whether two FDs are > backed by the same file *description*. See [1] for details. > Thanks for the correction and the reference. Seems like I've short circuited file description table vs file descriptor. Emil
