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SubjectRe: strace of io_uring events?
On Wed, Jul 15, 2020 at 07:35:50AM -0700, Andy Lutomirski wrote:
> > On Jul 15, 2020, at 4:12 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> >
> > <feff>Hi,

feff? Are we doing WTF-16 in email now? ;-)

> >
> > This thread is to discuss the possibility of stracing requests
> > submitted through io_uring. I'm not directly involved in io_uring
> > development, so I'm posting this out of interest in using strace on
> > processes utilizing io_uring.
> >
> > io_uring gives the developer a way to bypass the syscall interface,
> > which results in loss of information when tracing. This is a strace
> > fragment on "io_uring-cp" from liburing:
> >
> > io_uring_enter(5, 40, 0, 0, NULL, 8) = 40
> > io_uring_enter(5, 1, 0, 0, NULL, 8) = 1
> > io_uring_enter(5, 1, 0, 0, NULL, 8) = 1
> > ...
> >
> > What really happens are read + write requests. Without that
> > information the strace output is mostly useless.
> >
> > This loss of information is not new, e.g. calls through the vdso or
> > futext fast paths are also invisible to strace. But losing filesystem
> > I/O calls are a major blow, imo.
> >
> > What do people think?
> >
> > From what I can tell, listing the submitted requests on
> > io_uring_enter() would not be hard. Request completion is
> > asynchronous, however, and may not require io_uring_enter() syscall.
> > Am I correct?
> >
> > Is there some existing tracing infrastructure that strace could use to
> > get async completion events? Should we be introducing one?
> >
> >
>
> Let’s add some seccomp folks. We probably also want to be able to run seccomp-like filters on io_uring requests. So maybe io_uring should call into seccomp-and-tracing code for each action.

Adding Stefano since he had a complementary proposal for iouring
restrictions that weren't exactly seccomp.

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