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libbpf: Use BPF perf link when supported by kernel 

Detect kernel support for BPF perf link and prefer it when attaching to
perf_event, tracepoint, kprobe/uprobe. Underlying perf_event FD will be kept
open until BPF link is destroyed, at which point both perf_event FD and BPF
link FD will be closed.

This preserves current behavior in which perf_event FD is open for the
duration of bpf_link's lifetime and user is able to "disconnect" bpf_link from
underlying FD (with bpf_link__disconnect()), so that bpf_link__destroy()
doesn't close underlying perf_event FD.When BPF perf link is used, disconnect
will keep both perf_event and bpf_link FDs open, so it will be up to
(advanced) user to close them. This approach is demonstrated in bpf_cookie.c
selftests, added in this patch set.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210815070609.987780-10-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2021-08-15 00:06:02 -07:00 committed by Daniel Borkmann
parent d88b71d4a9
commit 668ace0ea5
1 changed files with 91 additions and 22 deletions
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113
tools/lib/bpf/libbpf.c
View File

@ -193,6 +193,8 @@ enum kern_feature_id {
FEAT_MODULE_BTF,
/* BTF_KIND_FLOAT support */
FEAT_BTF_FLOAT,
/* BPF perf link support */
FEAT_PERF_LINK,
__FEAT_CNT,
};
@ -4337,6 +4339,37 @@ static int probe_module_btf(void)
return !err;
}
static int probe_perf_link(void)
{
struct bpf_load_program_attr attr;
struct bpf_insn insns[] = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
};
int prog_fd, link_fd, err;
memset(&attr, 0, sizeof(attr));
attr.prog_type = BPF_PROG_TYPE_TRACEPOINT;
attr.insns = insns;
attr.insns_cnt = ARRAY_SIZE(insns);
attr.license = "GPL";
prog_fd = bpf_load_program_xattr(&attr, NULL, 0);
if (prog_fd < 0)
return -errno;
/* use invalid perf_event FD to get EBADF, if link is supported;
* otherwise EINVAL should be returned
*/
link_fd = bpf_link_create(prog_fd, -1, BPF_PERF_EVENT, NULL);
err = -errno; /* close() can clobber errno */
if (link_fd >= 0)
close(link_fd);
close(prog_fd);
return link_fd < 0 && err == -EBADF;
}
enum kern_feature_result {
FEAT_UNKNOWN = 0,
FEAT_SUPPORTED = 1,
@ -4387,6 +4420,9 @@ static struct kern_feature_desc {
[FEAT_BTF_FLOAT] = {
"BTF_KIND_FLOAT support", probe_kern_btf_float,
},
[FEAT_PERF_LINK] = {
"BPF perf link support", probe_perf_link,
},
};
static bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id)
@ -8951,23 +8987,38 @@ int bpf_link__unpin(struct bpf_link *link)
return 0;
}
static int bpf_link__detach_perf_event(struct bpf_link *link)
{
int err;
struct bpf_link_perf {
struct bpf_link link;
int perf_event_fd;
};
err = ioctl(link->fd, PERF_EVENT_IOC_DISABLE, 0);
if (err)
static int bpf_link_perf_detach(struct bpf_link *link)
{
struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);
int err = 0;
if (ioctl(perf_link->perf_event_fd, PERF_EVENT_IOC_DISABLE, 0) < 0)
err = -errno;
if (perf_link->perf_event_fd != link->fd)
close(perf_link->perf_event_fd);
close(link->fd);
return libbpf_err(err);
}
static void bpf_link_perf_dealloc(struct bpf_link *link)
{
struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);
free(perf_link);
}
struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog, int pfd)
{
char errmsg[STRERR_BUFSIZE];
struct bpf_link *link;
int prog_fd, err;
struct bpf_link_perf *link;
int prog_fd, link_fd = -1, err;
if (pfd < 0) {
pr_warn("prog '%s': invalid perf event FD %d\n",
@ -8984,27 +9035,45 @@ struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog, int pf
link = calloc(1, sizeof(*link));
if (!link)
return libbpf_err_ptr(-ENOMEM);
link->detach = &bpf_link__detach_perf_event;
link->fd = pfd;
link->link.detach = &bpf_link_perf_detach;
link->link.dealloc = &bpf_link_perf_dealloc;
link->perf_event_fd = pfd;
if (ioctl(pfd, PERF_EVENT_IOC_SET_BPF, prog_fd) < 0) {
err = -errno;
free(link);
pr_warn("prog '%s': failed to attach to pfd %d: %s\n",
prog->name, pfd, libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
if (err == -EPROTO)
pr_warn("prog '%s': try add PERF_SAMPLE_CALLCHAIN to or remove exclude_callchain_[kernel|user] from pfd %d\n",
prog->name, pfd);
return libbpf_err_ptr(err);
if (kernel_supports(prog->obj, FEAT_PERF_LINK)) {
link_fd = bpf_link_create(prog_fd, pfd, BPF_PERF_EVENT, NULL);
if (link_fd < 0) {
err = -errno;
pr_warn("prog '%s': failed to create BPF link for perf_event FD %d: %d (%s)\n",
prog->name, pfd,
err, libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
goto err_out;
}
link->link.fd = link_fd;
} else {
if (ioctl(pfd, PERF_EVENT_IOC_SET_BPF, prog_fd) < 0) {
err = -errno;
pr_warn("prog '%s': failed to attach to perf_event FD %d: %s\n",
prog->name, pfd, libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
if (err == -EPROTO)
pr_warn("prog '%s': try add PERF_SAMPLE_CALLCHAIN to or remove exclude_callchain_[kernel|user] from pfd %d\n",
prog->name, pfd);
goto err_out;
}
link->link.fd = pfd;
}
if (ioctl(pfd, PERF_EVENT_IOC_ENABLE, 0) < 0) {
err = -errno;
free(link);
pr_warn("prog '%s': failed to enable pfd %d: %s\n",
pr_warn("prog '%s': failed to enable perf_event FD %d: %s\n",
prog->name, pfd, libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
return libbpf_err_ptr(err);
goto err_out;
}
return link;
return &link->link;
err_out:
if (link_fd >= 0)
close(link_fd);
free(link);
return libbpf_err_ptr(err);
}
/*