[PATCH bpf-next v3 08/21] bpf: implement common macros/helpers for target iterators

Yonghong Song
2020-05-07T05:40:30Z

Macro DEFINE_BPF_ITER_FUNC is implemented so target
can define an init function to capture the BTF type
which represents the target.

The bpf_iter_meta is a structure holding meta data, common
to all targets in the bpf program.

Additional marker functions are called before or after
bpf_seq_read() show()/next()/stop() callback functions
to help calculate precise seq_num and whether call bpf_prog
inside stop().

Two functions, bpf_iter_get_info() and bpf_iter_run_prog(),
are implemented so target can get needed information from
bpf_iter infrastructure and can run the program.

Signed-off-by: Yonghong Song <yhs@fb.com>
---
include/linux/bpf.h | 11 ++++++
kernel/bpf/bpf_iter.c | 86 ++++++++++++++++++++++++++++++++++++++++---
2 files changed, 92 insertions(+), 5 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index b06653ab3476..ffe0b9b669bf 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1129,6 +1129,9 @@ int bpf_obj_pin_user(u32 ufd, const char __user *pathname);
int bpf_obj_get_user(const char __user *pathname, int flags);

#define BPF_ITER_FUNC_PREFIX "__bpf_iter__"
+#define DEFINE_BPF_ITER_FUNC(target, args...) \
+ extern int __bpf_iter__ ## target(args); \
+ int __init __bpf_iter__ ## target(args) { return 0; }

typedef int (*bpf_iter_init_seq_priv_t)(void *private_data);
typedef void (*bpf_iter_fini_seq_priv_t)(void *private_data);
@@ -1141,12 +1144,20 @@ struct bpf_iter_reg {
u32 seq_priv_size;
};

+struct bpf_iter_meta {
+ __bpf_md_ptr(struct seq_file *, seq);
+ u64 session_id;
+ u64 seq_num;
+};
+
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_iter_new_fd(struct bpf_link *link);
bool bpf_link_is_iter(struct bpf_link *link);
+struct bpf_prog *bpf_iter_get_info(struct bpf_iter_meta *meta, bool in_stop);
+int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx);

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/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index b0b8726c08f8..bf4fb7d7267b 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -41,6 +41,33 @@ static atomic64_t session_id;

static int prepare_seq_file(struct file *file, struct bpf_iter_link *link);

+static void bpf_iter_inc_seq_num(struct seq_file *seq)
+{
+ struct bpf_iter_priv_data *iter_priv;
+
+ iter_priv = container_of(seq->private, struct bpf_iter_priv_data,
+ target_private);
+ iter_priv->seq_num++;
+}
+
+static void bpf_iter_dec_seq_num(struct seq_file *seq)
+{
+ struct bpf_iter_priv_data *iter_priv;
+
+ iter_priv = container_of(seq->private, struct bpf_iter_priv_data,
+ target_private);
+ iter_priv->seq_num--;
+}
+
+static void bpf_iter_done_stop(struct seq_file *seq)
+{
+ struct bpf_iter_priv_data *iter_priv;
+
+ iter_priv = container_of(seq->private, struct bpf_iter_priv_data,
+ target_private);
+ iter_priv->done_stop = true;
+}
+
/* bpf_seq_read, a customized and simpler version for bpf iterator.
* no_llseek is assumed for this file.
* The following are differences from seq_read():
@@ -87,6 +114,10 @@ static ssize_t bpf_seq_read(struct file *file, char __user *buf, size_t size,

err = seq->op->show(seq, p);
if (err > 0) {
+ /* object is skipped, decrease seq_num, so next
+ * valid object can reuse the same seq_num.
+ */
+ bpf_iter_dec_seq_num(seq);
seq->count = 0;
} else if (err < 0 || seq_has_overflowed(seq)) {
if (!err)
@@ -112,11 +143,16 @@ static ssize_t bpf_seq_read(struct file *file, char __user *buf, size_t size,
err = PTR_ERR(p);
break;
}
+
+ /* get a valid next object, increase seq_num */
+ bpf_iter_inc_seq_num(seq);
+
if (seq->count >= size)
break;

err = seq->op->show(seq, p);
if (err > 0) {
+ bpf_iter_dec_seq_num(seq);
seq->count = offs;
} else if (err < 0 || seq_has_overflowed(seq)) {
seq->count = offs;
@@ -133,11 +169,15 @@ static ssize_t bpf_seq_read(struct file *file, char __user *buf, size_t size,
offs = seq->count;
/* bpf program called if !p */
seq->op->stop(seq, p);
- if (!p && seq_has_overflowed(seq)) {
- seq->count = offs;
- if (offs == 0) {
- err = -E2BIG;
- goto done;
+ if (!p) {
+ if (!seq_has_overflowed(seq)) {
+ bpf_iter_done_stop(seq);
+ } else {
+ seq->count = offs;
+ if (offs == 0) {
+ err = -E2BIG;
+ goto done;
+ }
}
}

@@ -448,3 +488,39 @@ int bpf_iter_new_fd(struct bpf_link *link)
put_unused_fd(fd);
return err;
}
+
+struct bpf_prog *bpf_iter_get_info(struct bpf_iter_meta *meta, bool in_stop)
+{
+ struct bpf_iter_priv_data *iter_priv;
+ struct seq_file *seq;
+ void *seq_priv;
+
+ seq = meta->seq;
+ if (seq->file->f_op != &bpf_iter_fops)
+ return NULL;
+
+ seq_priv = seq->private;
+ iter_priv = container_of(seq_priv, struct bpf_iter_priv_data,
+ target_private);
+
+ if (in_stop && iter_priv->done_stop)
+ return NULL;
+
+ meta->session_id = iter_priv->session_id;
+ meta->seq_num = iter_priv->seq_num;
+
+ return iter_priv->prog;
+}
+
+int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx)
+{
+ int ret;
+
+ rcu_read_lock();
+ migrate_disable();
+ ret = BPF_PROG_RUN(prog, ctx);
+ migrate_enable();
+ rcu_read_unlock();
+
+ return ret == 0 ? 0 : -EAGAIN;
+}
--
2.24.1