Re: [PATCH 2/9] perf/core: Add PERF_SAMPLE_CGROUP feature

[Tejun Heo]

On Fri, Dec 20, 2019 at 01:32:46PM +0900, Namhyung Kim wrote:
> The PERF_SAMPLE_CGROUP bit is to save (perf_event) cgroup information
> in the sample.  It will add a 64-bit id to identify current cgroup and
> it's the file handle in the cgroup file system.  Userspace should use
> this information with PERF_RECORD_CGROUP event to match which cgroup
> it belongs.

You don't need PERF_RECORD_CGROUP for that.  Something like the
following should work.

	struct {
		struct file_handle fh;
		char stor[MAX_HANDLE_SZ];
	} fh_store;
	struct file_handle *fh = &fh_store;

	fh->handle_type = 0xfe; // FILEID_KERNFS
	fh->handle_bytes = sizeof(u64);
	*(u64 *)fh->f_handle = cgrp_id;

	mnt_fd = open('/sys/fs/cgroup', O_RDONLY);
	fd = open_by_handle_at(mnt_fd, fh, O_RDONLY);

	snprintf(proc_path, PATH_MAX, "/proc/self/fd/%d", fd);
	readlink(proc_path, cgrp_path, PATH_MAX);

-- 
tejun