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From:   Jeff Moyer <jmoyer@redhat.com>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     "linux-block\@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: Re: [PATCH] io_uring: add support for IORING_REGISTER_FILES_UPDATE
References: <a7bc8d7f-2379-7492-93af-6ca0353c5eab@kernel.dk>
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Date:   Fri, 04 Oct 2019 11:34:19 -0400
In-Reply-To: <a7bc8d7f-2379-7492-93af-6ca0353c5eab@kernel.dk> (Jens Axboe's
        message of "Fri, 4 Oct 2019 08:52:52 -0600")
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Jens Axboe <axboe@kernel.dk> writes:

> Allows the application to remove/replace/add files to/from a file set.
> Passes in a struct:
>
> struct io_uring_files_update {
>         __u32 offset;
>         __s32 *fds;
> };
>
> that holds an array of fds, size of array passed in through the usual
> nr_args part of the io_uring_register() system call. The logic is as
> follows:
>
> 1) If ->fds[i] is -1, the existing file at i + ->offset is removed from
>    the set.
> 2) If ->fds[i] is a valid fd, the existing file at i + ->offset is
>    replaced with ->fds[i].
>
> For case #2, is the existing file is currently empty (fd == -1), the
> new fd is simply added to the array.

If I'm reading this (and the code) right, that means you can't add files
to a set.  Wouldn't that be a useful thing to do, instead of just
replacing existing ones?

Can you post the man page update along with this?

Thanks,
Jeff