2020-06-17 09:18 UTC-0700 ~ Andrii Nakryiko <andriin@xxxxxx>
> Add bpf_iter-based way to find all the processes that hold open FDs against
> BPF object (map, prog, link, btf). bpftool always attempts to discover this,
> but will silently give up if kernel doesn't yet support bpf_iter BPF programs.
> Process name and PID are emitted for each process (task group).
>
> Sample output for each of 4 BPF objects:
>
> $ sudo ./bpftool prog show
> 2694: cgroup_device tag 8c42dee26e8cd4c2 gpl
> loaded_at 2020-06-16T15:34:32-0700 uid 0
> xlated 648B jited 409B memlock 4096B
> pids systemd(1)
> 2907: cgroup_skb name egress tag 9ad187367cf2b9e8 gpl
> loaded_at 2020-06-16T18:06:54-0700 uid 0
> xlated 48B jited 59B memlock 4096B map_ids 2436
> btf_id 1202
> pids test_progs(2238417), test_progs(2238445)
>
> $ sudo ./bpftool map show
> 2436: array name test_cgr.bss flags 0x400
> key 4B value 8B max_entries 1 memlock 8192B
> btf_id 1202
> pids test_progs(2238417), test_progs(2238445)
> 2445: array name pid_iter.rodata flags 0x480
> key 4B value 4B max_entries 1 memlock 8192B
> btf_id 1214 frozen
> pids bpftool(2239612)
>
> $ sudo ./bpftool link show
> 61: cgroup prog 2908
> cgroup_id 375301 attach_type egress
> pids test_progs(2238417), test_progs(2238445)
> 62: cgroup prog 2908
> cgroup_id 375344 attach_type egress
> pids test_progs(2238417), test_progs(2238445)
>
> $ sudo ./bpftool btf show
> 1202: size 1527B prog_ids 2908,2907 map_ids 2436
> pids test_progs(2238417), test_progs(2238445)
> 1242: size 34684B
> pids bpftool(2258892)
>
> Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
> ---
[...]
> diff --git a/tools/bpf/bpftool/pids.c b/tools/bpf/bpftool/pids.c
> new file mode 100644
> index 000000000000..3474a91743ff
> --- /dev/null
> +++ b/tools/bpf/bpftool/pids.c
> @@ -0,0 +1,229 @@
[...]
> +int build_obj_refs_table(struct obj_refs_table *table, enum bpf_obj_type type)
> +{
> + char buf[4096];
> + struct pid_iter_bpf *skel;
> + struct pid_iter_entry *e;
> + int err, ret, fd = -1, i;
> + libbpf_print_fn_t default_print;
> +
> + hash_init(table->table);
> + set_max_rlimit();
> +
> + skel = pid_iter_bpf__open();
> + if (!skel) {
> + p_err("failed to open PID iterator skeleton");
> + return -1;
> + }
> +
> + skel->rodata->obj_type = type;
> +
> + /* we don't want output polluted with libbpf errors if bpf_iter is not
> + * supported
> + */
> + default_print = libbpf_set_print(libbpf_print_none);
> + err = pid_iter_bpf__load(skel);
> + libbpf_set_print(default_print);
> + if (err) {
> + /* too bad, kernel doesn't support BPF iterators yet */
> + err = 0;
> + goto out;
> + }
> + err = pid_iter_bpf__attach(skel);
> + if (err) {
> + /* if we loaded above successfully, attach has to succeed */
> + p_err("failed to attach PID iterator: %d", err);
Nit: What about using strerror(err) for the error messages, here and
below? It's easier to read than an integer value.
> + goto out;
> + }
> +
> + fd = bpf_iter_create(bpf_link__fd(skel->links.iter));
> + if (fd < 0) {
> + err = -errno;
> + p_err("failed to create PID iterator session: %d", err);
> + goto out;
> + }
> +
> + while (true) {
> + ret = read(fd, buf, sizeof(buf));
> + if (ret < 0) {
> + err = -errno;
> + p_err("failed to read PID iterator output: %d", err);
> + goto out;
> + }
> + if (ret == 0)
> + break;
> + if (ret % sizeof(*e)) {
> + err = -EINVAL;
> + p_err("invalid PID iterator output format");
> + goto out;
> + }
> + ret /= sizeof(*e);
> +
> + e = (void *)buf;
> + for (i = 0; i < ret; i++, e++) {
> + add_ref(table, e);
> + }
> + }
> + err = 0;
> +out:
> + if (fd >= 0)
> + close(fd);
> + pid_iter_bpf__destroy(skel);
> + return err;
> +}
[...]
> diff --git a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
> new file mode 100644
> index 000000000000..f560e48add07
> --- /dev/null
> +++ b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
> @@ -0,0 +1,80 @@
> +// SPDX-License-Identifier: GPL-2.0
This would make it the only file not dual-licensed GPL/BSD in bpftool.
We've had issues with that before [0], although linking to libbfd is no
more a hard requirement. But I see you used a dual-license in the
corresponding header file pid_iter.h, so is the single license
intentional here? Or would you consider GPL/BSD?
[0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=896165#38
> +// Copyright (c) 2020 Facebook
> +#include <vmlinux.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_core_read.h>
> +#include <bpf/bpf_tracing.h>
> +#include "pid_iter.h"
[...]
> +
> +char LICENSE[] SEC("license") = "GPL";
> diff --git a/tools/bpf/bpftool/skeleton/pid_iter.h b/tools/bpf/bpftool/skeleton/pid_iter.h
> new file mode 100644
> index 000000000000..5692cf257adb
> --- /dev/null
> +++ b/tools/bpf/bpftool/skeleton/pid_iter.h
> @@ -0,0 +1,12 @@
> +/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) */
[...]
