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From:   "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Date:   Wed, 22 Apr 2020 08:06:30 +0200
Message-ID: <CAKgNAki3uoai+FWTQv6+DdQjCF3nc+7HoUZrLSC5dEf3ob9uRA@mail.gmail.com>
Subject: Re: [PATCH v5 3/3] fs: pipe2: Support O_SPECIFIC_FD
To:     Josh Triplett <josh@joshtriplett.org>
Cc:     io-uring@vger.kernel.org,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Arnd Bergmann <arnd@arndb.de>, Jens Axboe <axboe@kernel.dk>,
        Aleksa Sarai <cyphar@cyphar.com>,
        linux-man <linux-man@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>
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[CC += linux-api]

On Wed, 22 Apr 2020 at 07:20, Josh Triplett <josh@joshtriplett.org> wrote:
>
> This allows the caller of pipe2 to specify one or both file descriptors
> rather than having them automatically use the lowest available file
> descriptor. The caller can specify either file descriptor as -1 to
> allow that file descriptor to use the lowest available.
>
> Signed-off-by: Josh Triplett <josh@joshtriplett.org>
> ---
>  fs/pipe.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 16fb72e9abf7..4681a0d1d587 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -936,19 +936,19 @@ static int __do_pipe_flags(int *fd, struct file **files, int flags)
>         int error;
>         int fdw, fdr;
>
> -       if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT))
> +       if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT | O_SPECIFIC_FD))
>                 return -EINVAL;
>
>         error = create_pipe_files(files, flags);
>         if (error)
>                 return error;
>
> -       error = get_unused_fd_flags(flags);
> +       error = get_specific_unused_fd_flags(fd[0], flags);
>         if (error < 0)
>                 goto err_read_pipe;
>         fdr = error;
>
> -       error = get_unused_fd_flags(flags);
> +       error = get_specific_unused_fd_flags(fd[1], flags);
>         if (error < 0)
>                 goto err_fdr;
>         fdw = error;
> @@ -969,7 +969,11 @@ static int __do_pipe_flags(int *fd, struct file **files, int flags)
>  int do_pipe_flags(int *fd, int flags)
>  {
>         struct file *files[2];
> -       int error = __do_pipe_flags(fd, files, flags);
> +       int error;
> +
> +       if (flags & O_SPECIFIC_FD)
> +               return -EINVAL;
> +       error = __do_pipe_flags(fd, files, flags);
>         if (!error) {
>                 fd_install(fd[0], files[0]);
>                 fd_install(fd[1], files[1]);
> @@ -987,6 +991,10 @@ static int do_pipe2(int __user *fildes, int flags)
>         int fd[2];
>         int error;
>
> +       if (flags & O_SPECIFIC_FD)
> +               if (copy_from_user(fd, fildes, sizeof(fd)))
> +                       return -EFAULT;
> +
>         error = __do_pipe_flags(fd, files, flags);
>         if (!error) {
>                 if (unlikely(copy_to_user(fildes, fd, sizeof(fd)))) {
> --
> 2.26.2
>


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/