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Date:   Fri, 14 Jul 2023 17:47:45 +0200
From:   Christian Brauner <brauner@kernel.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Arnd Bergmann <arnd@arndb.de>, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/5] io_uring: add IORING_OP_WAITID support
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On Tue, Jul 11, 2023 at 04:18:13PM -0600, Jens Axboe wrote:
> On 7/11/23 3:22 PM, Jens Axboe wrote:
> > On 7/11/23 3:11?PM, Arnd Bergmann wrote:
> >> On Tue, Jul 11, 2023, at 22:43, Jens Axboe wrote:
> >>> This adds support for an async version of waitid(2), in a fully async
> >>> version. If an event isn't immediately available, wait for a callback
> >>> to trigger a retry.
> >>>
> >>> The format of the sqe is as follows:
> >>>
> >>> sqe->len		The 'which', the idtype being queried/waited for.
> >>> sqe->fd			The 'pid' (or id) being waited for.
> >>> sqe->file_index		The 'options' being set.
> >>> sqe->addr2		A pointer to siginfo_t, if any, being filled in.
> >>>
> >>> buf_index, add3, and waitid_flags are reserved/unused for now.
> >>> waitid_flags will be used for options for this request type. One
> >>> interesting use case may be to add multi-shot support, so that the
> >>> request stays armed and posts a notification every time a monitored
> >>> process state change occurs.
> >>>
> >>> Note that this does not support rusage, on Arnd's recommendation.
> >>>
> >>> See the waitid(2) man page for details on the arguments.
> >>>
> >>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> >>
> >> Does this require argument conversion for compat tasks?
> >>
> >> Even without the rusage argument, I think the siginfo
> >> remains incompatible with 32-bit tasks, unfortunately.
> > 
> > Hmm yes good point, if compat_siginfo and siginfo are different, then it
> > does need handling for that. Would be a trivial addition, I'll make that
> > change. Thanks Arnd!
> 
> Should be fixed in the current version:
> 
> https://git.kernel.dk/cgit/linux/commit/?h=io_uring-waitid&id=08f3dc9b7cedbd20c0f215f25c9a7814c6c601cc

In kernel/signal.c in pidfd_send_signal() we have
copy_siginfo_from_user_any() it seems that a similar version
copy_siginfo_to_user_any() might be something to consider. We do have
copy_siginfo_to_user32() and copy_siginfo_to_user(). But I may lack
context why this wouldn't work here.