Re: [PATCHSET cgroup/for-5.5] kernfs,cgroup: support 64bit inos and unify cgroup IDs

Namhyung Kim
2019-11-06T13:50:30Z

Hi Tejun,

On Tue, Nov 5, 2019 at 8:59 AM Tejun Heo <tj@kernel.org> wrote:
>
> Hello,
>
> Currently, there are three IDs which are being used to identify a
> cgroup.
>
> 1. cgroup->id
> 2. cgroupfs 32bit ino
> 3. cgroupfs 32bit ino + 32bit gen
>
> All three IDs are visible to userland through different interfaces.
> This is very confusing and #1 can't even be resolved to cgroups from
> userland.
>
> A 64bit number is sufficient to identify a cgroup instance uniquely
> and ino_t is 64bit on all archs except for alpha. There's no reason
> for three different IDs at all. This patchset updates kernfs so that
> it supports 64bit ino and associated exportfs operations and unifies
> the cgroup IDs.
>
> * On 64bit ino archs, ino is kernfs node ID which is also the cgroup
> ID. The ino can be passed directly into open_by_handle_at(2) w/ the
> new key type FILEID_KERNFS. Backward compatibility is maintained
> for FILEID_INO32_GEN keys.
>
> * On 32bit ino archs, kernfs node ID is still 64bit and the cgroup ID.
> ino is the low 32bits and gen is the high 32bits. If the high
> 32bits is zero, open_by_handle_at(2) only matches the ino part of
> the ID allowing userland to resolve inos to cgroups as long as
> distinguishing recycled inos isn't necessary.
>
> This patchset contains the following 10 patches.
>
> 0001-kernfs-fix-ino-wrap-around-detection.patch
> 0002-writeback-use-ino_t-for-inodes-in-tracepoints.patch
> 0003-netprio-use-css-ID-instead-of-cgroup-ID.patch
> 0004-kernfs-use-dumber-locking-for-kernfs_find_and_get_no.patch
> 0005-kernfs-kernfs_find_and_get_node_by_ino-should-only-l.patch
> 0006-kernfs-convert-kernfs_node-id-from-union-kernfs_node.patch
> 0007-kernfs-combine-ino-id-lookup-functions-into-kernfs_f.patch
> 0008-kernfs-implement-custom-exportfs-ops-and-fid-type.patch
> 0009-kernfs-use-64bit-inos-if-ino_t-is-64bit.patch
> 0010-cgroup-use-cgrp-kn-id-as-the-cgroup-ID.patch
>
> 0001 is a fix which should be backported through -stable. 0002 and
> 0003 are prep patches. 0004-0009 make kernfs_node->id a u64 and use
> it as ino on 64bit ino archs. 0010 replaces cgroup->id with the
> kernfs node ID.
>
> Greg, how do you want to route the patches? We can route 0001-0009
> through your tree and the last one through cgroup after pulling in.
> I'd be happy to route them all too.
>
> This patchset is also available in the following git branch.
>
> git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-unified-cgid
>
> diffstat follows. Thanks.

Thanks a lot for doing this! I've tested it with my perf cgroup patchset
based on top of this series and it looks good. You can add my

Tested-by: Namhyung Kim <namhyung@kernel.org>

Thanks
Namhyung