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

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