Hey, /* v2 summary */ Move put_user() into copy process before clone's point of no return so that we can handle put_user() errors as suggested by Oleg. The good news is that this again allows us to make the patch smaller. /* v1 summary */ As suggested by Oleg, have pidfds returned in the fourth argument of clone allowing us to return a pidfd and its pid to the caller at the same time. This has various advantages: - callers get the associated pid for the pidfd without additional parsing This makes it easier for userspce to get metadata access through procfs. - the type of the return value for clone() remains unchanged (was changed to return an fd in the previous iteration) - pid file descriptor numbering can start at 0 as is customary for file descriptors (was changed to start at 1 in the previous patchset to not break fork()-like error checking when returning pidfds) - finally, the patchset has gotten smaller The patchset makes it possible to retrieve pid file descriptors at process creation time by introducing the new flag CLONE_PIDFD to the clone() system call as previously discussed. As decided last week [1] Jann and I have refined the implementation of pidfds as anonymous inodes. Based on last weeks RFC we have only tweaked documentation and naming, as well as making the sample program how to get easy metadata access from a pidfd a little cleaner and more paranoid when checking for errors. The sample program can also serve as a test for the patchset. When clone is called with CLONE_PIDFD a pidfd will be returned in the fourth argument of clone. This is based on an idea from Oleg. It allows us to return a pidfd and the associated pid to the caller at the same time. We have taken care that pidfds are created *after* the fd table has been unshared to not leak pidfds into child processes. The actual code for CLONE_PIDFD in patch 2 is completely confined to fork.c (apart from the CLONE_PIDFD definition of course) and is rather small and hopefully good to review. The additional changes listed under David's name in the diffstat below are here to make anon_inodes available unconditionally. They are needed for the new mount api and thus for core vfs code in addition to pidfds. David knows this and he has informed Al that this patch is sent out here. The changes themselves are rather automatic. As promised I have also contacted Joel who has sent a patchset to make pidfds pollable. He has been informed and is happy to port his patchset once we have moved forward [2]. Jann and I currently plan to target this patchset for inclusion in the 5.2 merge window. Thanks! Jann & Christian [1]: https://lore.kernel.org/lkml/CAHk-=wifyY+XGNW=ZC4MyTHD14w81F8JjQNH-GaGAm2RxZ_S8Q@xxxxxxxxxxxxxx/ [2]: https://lore.kernel.org/lkml/20190411200059.GA75190@xxxxxxxxxx/ Christian Brauner (4): clone: add CLONE_PIDFD signal: use fdget() since we don't allow O_PATH signal: support CLONE_PIDFD with pidfd_send_signal samples: show race-free pidfd metadata access David Howells (1): Make anon_inodes unconditional arch/arm/kvm/Kconfig | 1 - arch/arm64/kvm/Kconfig | 1 - arch/mips/kvm/Kconfig | 1 - arch/powerpc/kvm/Kconfig | 1 - arch/s390/kvm/Kconfig | 1 - arch/x86/Kconfig | 1 - arch/x86/kvm/Kconfig | 1 - drivers/base/Kconfig | 1 - drivers/char/tpm/Kconfig | 1 - drivers/dma-buf/Kconfig | 1 - drivers/gpio/Kconfig | 1 - drivers/iio/Kconfig | 1 - drivers/infiniband/Kconfig | 1 - drivers/vfio/Kconfig | 1 - fs/Makefile | 2 +- fs/notify/fanotify/Kconfig | 1 - fs/notify/inotify/Kconfig | 1 - include/linux/pid.h | 2 + include/uapi/linux/sched.h | 1 + init/Kconfig | 10 --- kernel/fork.c | 96 ++++++++++++++++++++++++++-- kernel/signal.c | 14 +++-- kernel/sys_ni.c | 3 - samples/Makefile | 2 +- samples/pidfd/Makefile | 6 ++ samples/pidfd/pidfd-metadata.c | 112 +++++++++++++++++++++++++++++++++ 26 files changed, 225 insertions(+), 39 deletions(-) create mode 100644 samples/pidfd/Makefile create mode 100644 samples/pidfd/pidfd-metadata.c -- 2.21.0
