Re: [PATCH v9 0/4] Add pidfd_getfd syscall

On Tue, Jan 07, 2020 at 09:54:49PM +0100, Christian Brauner wrote:

On Tue, Jan 07, 2020 at 09:59:23AM -0800, Sargun Dhillon wrote:

quoted

This patchset introduces a mechanism (pidfd_getfd syscall) to get file
descriptors from other processes via pidfd. Although this can be achieved
using SCM_RIGHTS, and parasitic code injection, this offers a more
straightforward mechanism, with less overhead and complexity. The process
under manipulation's fd still remains valid, and unmodified by the
copy operation.

It introduces a flags field. The flags field is reserved a the moment,
but the intent is to extend it with the following capabilities:
 * Close the remote FD when copying it
 * Drop the cgroup data if it's a fd pointing a socket when copying it

The syscall numbers were chosen to be one greater than openat2.

Summary of history:
This initially started as a ptrace command. It did not require the process
to be stopped, and felt like kind of an awkward fit for ptrace. After that,
it moved to an ioctl on the pidfd. Given the core functionality, it made
sense to make it a syscall which did not require the process to be stopped.

Previous versions:
 V8: https://lore.kernel.org/lkml/20200103162928.5271-1-sargun@sargun.me/ (local)
 V7: https://lore.kernel.org/lkml/20191226180227.GA29389@ircssh-2.c.rugged-nimbus-611.internal/ (local)
 V6: https://lore.kernel.org/lkml/20191223210823.GA25083@ircssh-2.c.rugged-nimbus-611.internal/ (local)
 V5: https://lore.kernel.org/lkml/20191220232746.GA20215@ircssh-2.c.rugged-nimbus-611.internal/ (local)
 V4: https://lore.kernel.org/lkml/20191218235310.GA17259@ircssh-2.c.rugged-nimbus-611.internal/ (local)
 V3: https://lore.kernel.org/lkml/20191217005842.GA14379@ircssh-2.c.rugged-nimbus-611.internal/ (local)
 V2: https://lore.kernel.org/lkml/20191209070446.GA32336@ircssh-2.c.rugged-nimbus-611.internal/ (local)
 RFC V1: https://lore.kernel.org/lkml/20191205234450.GA26369@ircssh-2.c.rugged-nimbus-611.internal/ (local)

I don't see anything wrong with this series anymore:

Acked-by: Christian Brauner <redacted>

Other Acked-bys/Reviewed-bys and reviews of course strongly encouraged!
Christian

Fyi, I'm waiting a few days on a reply from Al.
Depending on his input the intent rn is to move this into my for-next
early next week.

Christian