[PATCH bpf-next v3 03/21] bpf: support bpf tracing/iter programs for BPF_LINK_CREATE

Yonghong Song
2020-05-07T05:40:24Z

Given a bpf program, the step to create an anonymous bpf iterator is:
- create a bpf_iter_link, which combines bpf program and the target.
In the future, there could be more information recorded in the link.
A link_fd will be returned to the user space.
- create an anonymous bpf iterator with the given link_fd.

The bpf_iter_link can be pinned to bpffs mount file system to
create a file based bpf iterator as well.

The benefit to use of bpf_iter_link:
- using bpf link simplifies design and implementation as bpf link
is used for other tracing bpf programs.
- for file based bpf iterator, bpf_iter_link provides a standard
way to replace underlying bpf programs.
- for both anonymous and free based iterators, bpf link query
capability can be leveraged.

The patch added support of tracing/iter programs for BPF_LINK_CREATE.
A new link type BPF_LINK_TYPE_ITER is added to facilitate link
querying. Currently, only prog_id is needed, so there is no
additional in-kernel show_fdinfo() and fill_link_info() hook
is needed for BPF_LINK_TYPE_ITER link.

Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
include/linux/bpf.h | 1 +
include/linux/bpf_types.h | 1 +
include/uapi/linux/bpf.h | 1 +
kernel/bpf/bpf_iter.c | 62 ++++++++++++++++++++++++++++++++++
kernel/bpf/syscall.c | 14 ++++++++
tools/include/uapi/linux/bpf.h | 1 +
6 files changed, 80 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f28bdd714754..e93d2d33c82c 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1143,6 +1143,7 @@ struct bpf_iter_reg {
int bpf_iter_reg_target(struct bpf_iter_reg *reg_info);
void bpf_iter_unreg_target(const char *target);
bool bpf_iter_prog_supported(struct bpf_prog *prog);
+int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);

int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value);
int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value);
diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
index 8345cdf553b8..29d22752fc87 100644
--- a/include/linux/bpf_types.h
+++ b/include/linux/bpf_types.h
@@ -124,3 +124,4 @@ BPF_LINK_TYPE(BPF_LINK_TYPE_TRACING, tracing)
#ifdef CONFIG_CGROUP_BPF
BPF_LINK_TYPE(BPF_LINK_TYPE_CGROUP, cgroup)
#endif
+BPF_LINK_TYPE(BPF_LINK_TYPE_ITER, iter)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 047b19fe716e..2bf33979f9ae 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -229,6 +229,7 @@ enum bpf_link_type {
BPF_LINK_TYPE_RAW_TRACEPOINT = 1,
BPF_LINK_TYPE_TRACING = 2,
BPF_LINK_TYPE_CGROUP = 3,
+ BPF_LINK_TYPE_ITER = 4,

MAX_BPF_LINK_TYPE,
};
diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index dec182d8395a..03f5832909db 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -15,6 +15,11 @@ struct bpf_iter_target_info {
u32 btf_id; /* cached value */
};

+struct bpf_iter_link {
+ struct bpf_link link;
+ struct bpf_iter_target_info *tinfo;
+};
+
static struct list_head targets = LIST_HEAD_INIT(targets);
static DEFINE_MUTEX(targets_mutex);

@@ -93,3 +98,60 @@ bool bpf_iter_prog_supported(struct bpf_prog *prog)

return supported;
}
+
+static void bpf_iter_link_release(struct bpf_link *link)
+{
+}
+
+static void bpf_iter_link_dealloc(struct bpf_link *link)
+{
+ struct bpf_iter_link *iter_link =
+ container_of(link, struct bpf_iter_link, link);
+
+ kfree(iter_link);
+}
+
+static const struct bpf_link_ops bpf_iter_link_lops = {
+ .release = bpf_iter_link_release,
+ .dealloc = bpf_iter_link_dealloc,
+};
+
+int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
+{
+ struct bpf_link_primer link_primer;
+ struct bpf_iter_target_info *tinfo;
+ struct bpf_iter_link *link;
+ bool existed = false;
+ u32 prog_btf_id;
+ int err;
+
+ if (attr->link_create.target_fd || attr->link_create.flags)
+ return -EINVAL;
+
+ prog_btf_id = prog->aux->attach_btf_id;
+ mutex_lock(&targets_mutex);
+ list_for_each_entry(tinfo, &targets, list) {
+ if (tinfo->btf_id == prog_btf_id) {
+ existed = true;
+ break;
+ }
+ }
+ mutex_unlock(&targets_mutex);
+ if (!existed)
+ return -ENOENT;
+
+ link = kzalloc(sizeof(*link), GFP_USER | __GFP_NOWARN);
+ if (!link)
+ return -ENOMEM;
+
+ bpf_link_init(&link->link, BPF_LINK_TYPE_ITER, &bpf_iter_link_lops, prog);
+ link->tinfo = tinfo;
+
+ err = bpf_link_prime(&link->link, &link_primer);
+ if (err) {
+ kfree(link);
+ return err;
+ }
+
+ return bpf_link_settle(&link_primer);
+}
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index bb1ab7da6103..6ffe2d8fb6c7 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2729,6 +2729,8 @@ attach_type_to_prog_type(enum bpf_attach_type attach_type)
case BPF_CGROUP_GETSOCKOPT:
case BPF_CGROUP_SETSOCKOPT:
return BPF_PROG_TYPE_CGROUP_SOCKOPT;
+ case BPF_TRACE_ITER:
+ return BPF_PROG_TYPE_TRACING;
default:
return BPF_PROG_TYPE_UNSPEC;
}
@@ -3729,6 +3731,15 @@ static int bpf_map_do_batch(const union bpf_attr *attr,
return err;
}

+static int tracing_bpf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
+{
+ if (attr->link_create.attach_type == BPF_TRACE_ITER &&
+ prog->expected_attach_type == BPF_TRACE_ITER)
+ return bpf_iter_link_attach(attr, prog);
+
+ return -EINVAL;
+}
+
#define BPF_LINK_CREATE_LAST_FIELD link_create.flags
static int link_create(union bpf_attr *attr)
{
@@ -3765,6 +3776,9 @@ static int link_create(union bpf_attr *attr)
case BPF_PROG_TYPE_CGROUP_SOCKOPT:
ret = cgroup_bpf_link_attach(attr, prog);
break;
+ case BPF_PROG_TYPE_TRACING:
+ ret = tracing_bpf_link_attach(attr, prog);
+ break;
default:
ret = -EINVAL;
}
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 047b19fe716e..2bf33979f9ae 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -229,6 +229,7 @@ enum bpf_link_type {
BPF_LINK_TYPE_RAW_TRACEPOINT = 1,
BPF_LINK_TYPE_TRACING = 2,
BPF_LINK_TYPE_CGROUP = 3,
+ BPF_LINK_TYPE_ITER = 4,

MAX_BPF_LINK_TYPE,
};
--
2.24.1