Re: [PATCH v6 09/11] fs/pipe.c: export create_pipe_files() and replace_fd()

[Jarkko Sakkinen]

On Thu, Nov 30, 2017 at 10:38:30AM -0800, James Bottomley wrote:
> 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.

Thank you. I'll take a peek.

/Jarkko