[PATCH] [RFC] bpf: tracing: new helper bpf_get_current_cgroup_ino
Y Song
ys114321 at gmail.com
Fri May 25 16:28:22 UTC 2018
On Fri, May 25, 2018 at 8:21 AM, Alban Crequy <alban at kinvolk.io> wrote:
> On Wed, May 23, 2018 at 4:34 AM Y Song <ys114321 at gmail.com> wrote:
>
>> I did a quick prototyping and the above interface seems working fine.
>
> Thanks! I gave your kernel patch & userspace program a try and it works for
> me on cgroup-v2.
>
> Also, I found out how to get my containers to use both cgroup-v1 and
> cgroup-v2 (by enabling systemd's hybrid cgroup mode and docker's
> '--exec-opt native.cgroupdriver=systemd' option). So I should be able to
> use the BPF helper function without having to add support for all the
> cgroup-v1 hierarchies.
Great. Will submit a formal patch soon.
>
>> The kernel change:
>> ===============
>
>> [yhs at localhost bpf-next]$ git diff
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index 97446bbe2ca5..669b7383fddb 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -1976,7 +1976,8 @@ union bpf_attr {
>> FN(fib_lookup), \
>> FN(sock_hash_update), \
>> FN(msg_redirect_hash), \
>> - FN(sk_redirect_hash),
>> + FN(sk_redirect_hash), \
>> + FN(get_current_cgroup_id),
>
>> /* integer value in 'imm' field of BPF_CALL instruction selects which
> helper
>> * function eBPF program intends to call
>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
>> index ce2cbbff27e4..e11e3298f911 100644
>> --- a/kernel/trace/bpf_trace.c
>> +++ b/kernel/trace/bpf_trace.c
>> @@ -493,6 +493,21 @@ static const struct bpf_func_proto
>> bpf_current_task_under_cgroup_proto = {
>> .arg2_type = ARG_ANYTHING,
>> };
>
>> +BPF_CALL_0(bpf_get_current_cgroup_id)
>> +{
>> + struct cgroup *cgrp = task_dfl_cgroup(current);
>> + if (!cgrp)
>> + return -EINVAL;
>> +
>> + return cgrp->kn->id.id;
>> +}
>> +
>> +static const struct bpf_func_proto bpf_get_current_cgroup_id_proto = {
>> + .func = bpf_get_current_cgroup_id,
>> + .gpl_only = false,
>> + .ret_type = RET_INTEGER,
>> +};
>> +
>> BPF_CALL_3(bpf_probe_read_str, void *, dst, u32, size,
>> const void *, unsafe_ptr)
>> {
>> @@ -563,6 +578,8 @@ tracing_func_proto(enum bpf_func_id func_id, const
>> struct bpf_prog *prog)
>> return &bpf_get_prandom_u32_proto;
>> case BPF_FUNC_probe_read_str:
>> return &bpf_probe_read_str_proto;
>> + case BPF_FUNC_get_current_cgroup_id:
>> + return &bpf_get_current_cgroup_id_proto;
>> default:
>> return NULL;
>> }
>
>> The following program can be used to print out a cgroup id given a cgroup
> path.
>> [yhs at localhost cg]$ cat get_cgroup_id.c
>> #define _GNU_SOURCE
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <sys/types.h>
>> #include <sys/stat.h>
>> #include <fcntl.h>
>
>> int main(int argc, char **argv)
>> {
>> int dirfd, err, flags, mount_id, fhsize;
>> struct file_handle *fhp;
>> char *pathname;
>
>> if (argc != 2) {
>> printf("usage: %s <cgroup_path>\n", argv[0]);
>> return 1;
>> }
>
>> pathname = argv[1];
>> dirfd = AT_FDCWD;
>> flags = 0;
>
>> fhsize = sizeof(*fhp);
>> fhp = malloc(fhsize);
>> if (!fhp)
>> return 1;
>
>> err = name_to_handle_at(dirfd, pathname, fhp, &mount_id, flags);
>> if (err >= 0) {
>> printf("error\n");
>> return 1;
>> }
>
>> fhsize = sizeof(struct file_handle) + fhp->handle_bytes;
>> fhp = realloc(fhp, fhsize);
>> if (!fhp)
>> return 1;
>
>> err = name_to_handle_at(dirfd, pathname, fhp, &mount_id, flags);
>> if (err < 0)
>> perror("name_to_handle_at");
>> else {
>> int i;
>
>> printf("dir = %s, mount_id = %d\n", pathname, mount_id);
>> printf("handle_bytes = %d, handle_type = %d\n", fhp->handle_bytes,
>> fhp->handle_type);
>> if (fhp->handle_bytes != 8)
>> return 1;
>
>> printf("cgroup_id = 0x%llx\n", *(unsigned long long
> *)fhp->f_handle);
>> }
>
>> return 0;
>> }
>> [yhs at localhost cg]$
>
>> Given a cgroup path, the user can get cgroup_id and use it in their bpf
>> program for filtering purpose.
>
>> I run a simple program t.c
>> int main() { while(1) sleep(1); return 0; }
>> in the cgroup v2 directory /home/yhs/tmp/yhs
>> none on /home/yhs/tmp type cgroup2 (rw,relatime,seclabel)
>
>> $ ./get_cgroup_id /home/yhs/tmp/yhs
>> dir = /home/yhs/tmp/yhs, mount_id = 124
>> handle_bytes = 8, handle_type = 1
>> cgroup_id = 0x1000006b2
>
>> // the below command to get cgroup_id from the kernel for the
>> // process compiled with t.c and ran under /home/yhs/tmp/yhs:
>> $ sudo ./trace.py -p 4067 '__x64_sys_nanosleep "cgid = %llx", $cgid'
>> PID TID COMM FUNC -
>> 4067 4067 a.out __x64_sys_nanosleep cgid = 1000006b2
>> 4067 4067 a.out __x64_sys_nanosleep cgid = 1000006b2
>> 4067 4067 a.out __x64_sys_nanosleep cgid = 1000006b2
>> ^C[yhs at localhost tools]$
>
>> The kernel and user space cgid matches. Will provide a
>> formal patch later.
>
>
>
>
>> On Mon, May 21, 2018 at 5:24 PM, Y Song <ys114321 at gmail.com> wrote:
>> > On Mon, May 21, 2018 at 9:26 AM, Alexei Starovoitov
>> > <alexei.starovoitov at gmail.com> wrote:
>> >> On Sun, May 13, 2018 at 07:33:18PM +0200, Alban Crequy wrote:
>> >>>
>> >>> +BPF_CALL_2(bpf_get_current_cgroup_ino, u32, hierarchy, u64, flags)
>> >>> +{
>> >>> + // TODO: pick the correct hierarchy instead of the mem
> controller
>> >>> + struct cgroup *cgrp = task_cgroup(current, memory_cgrp_id);
>> >>> +
>> >>> + if (unlikely(!cgrp))
>> >>> + return -EINVAL;
>> >>> + if (unlikely(hierarchy))
>> >>> + return -EINVAL;
>> >>> + if (unlikely(flags))
>> >>> + return -EINVAL;
>> >>> +
>> >>> + return cgrp->kn->id.ino;
>> >>
>> >> ino only is not enough to identify cgroup. It needs generation number
> too.
>> >> I don't quite see how hierarchy and flags can be used in the future.
>> >> Also why limit it to memcg?
>> >>
>> >> How about something like this instead:
>> >>
>> >> BPF_CALL_2(bpf_get_current_cgroup_id)
>> >> {
>> >> struct cgroup *cgrp = task_dfl_cgroup(current);
>> >>
>> >> return cgrp->kn->id.id;
>> >> }
>> >> The user space can use fhandle api to get the same 64-bit id.
>> >
>> > I think this should work. This will also be useful to bcc as user
>> > space can encode desired id
>> > in the bpf program and compared that id to the current cgroup id, so we
> can have
>> > cgroup level tracing (esp. stat collection) support. To cope with
>> > cgroup hierarchy, user can use
>> > cgroup-array based approach or explicitly compare against multiple
> cgroup id's.
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