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    SubjectRe: [PATCH v6 09/11] fs/pipe.c: export create_pipe_files() and replace_fd()
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    On Thu, 2017-11-30 at 18:43 +0200, Jarkko Sakkinen wrote:
    > On Wed, Nov 29, 2017 at 03:13:57PM -0800, Christoph Hellwig wrote:
    > >
    > > On Tue, Nov 28, 2017 at 11:57:53PM +0200, Jarkko Sakkinen wrote:
    > > >
    > > > >
    > > > > Yes.  You still shall not play nasty games with file
    > > > > descriptors.
    > > >
    > > > I need to put something to file descriptors in order to have a IO
    > > > channels for the launch enclave hosting process.
    > >
    > > Just do it like any other program - open it from your userspace
    > > program using open() and related syscalls.
    >
    > In this case it would not work as the launch enclave is still part of
    > the kernel and it would create a dependency how the user space
    > defines paths. If using pipe specifically is an issue, I could easily
    > use shmem file as a mean for communiation.

    Can't you simply use 

    sys_pipe2()
    sys_close()
    sys_dup2()

    To achieve the same effect as replace_fd()/create_pipe_files()?

    The point Christoph is making is that you can call sys_ interfaces from
    within the kernel (carefully) and have them operate like direct
    invocations.  Look at main.c:kernel_init_freeable() it's doing
    something similar to what you want, except with the console, not a pipe
    and it begins with the file table empty.

    James

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