[PATCH bpf-next v3 06/21] bpf: create anonymous bpf iterator

Yonghong Song
2020-05-07T05:39:29Z

A new bpf command BPF_ITER_CREATE is added.

The anonymous bpf iterator is seq_file based.
The seq_file private data are referenced by targets.
The bpf_iter infrastructure allocated additional space
at seq_file->private before the space used by targets
to store some meta data, e.g.,
prog: prog to run
session_id: an unique id for each opened seq_file
seq_num: how many times bpf programs are queried in this session
done_stop: an internal state to decide whether bpf program
should be called in seq_ops->stop() or not

The seq_num will start from 0 for valid objects.
The bpf program may see the same seq_num more than once if
- seq_file buffer overflow happens and the same object
is retried by bpf_seq_read(), or
- the bpf program explicitly requests a retry of the
same object

Since module is not supported for bpf_iter, all target
registeration happens at __init time, so there is no
need to change bpf_iter_unreg_target() as it is used
mostly in error path of the init function at which time
no bpf iterators have been created yet.

Signed-off-by: Yonghong Song <yhs@fb.com>
---
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 6 ++
kernel/bpf/bpf_iter.c | 129 +++++++++++++++++++++++++++++++++
kernel/bpf/syscall.c | 26 +++++++
tools/include/uapi/linux/bpf.h | 6 ++
5 files changed, 168 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index e93d2d33c82c..80b1b9d8a638 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1144,6 +1144,7 @@ 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);

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/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 2bf33979f9ae..97ceb0f2e539 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -116,6 +116,7 @@ enum bpf_cmd {
BPF_LINK_GET_FD_BY_ID,
BPF_LINK_GET_NEXT_ID,
BPF_ENABLE_STATS,
+ BPF_ITER_CREATE,
};

enum bpf_map_type {
@@ -614,6 +615,11 @@ union bpf_attr {
__u32 type;
} enable_stats;

+ struct { /* struct used by BPF_ITER_CREATE command */
+ __u32 link_fd;
+ __u32 flags;
+ } iter_create;
+
} __attribute__((aligned(8)));

/* The description below is an attempt at providing documentation to eBPF
diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index f198597b0ea4..917df4c69966 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -2,6 +2,7 @@
/* Copyright (c) 2020 Facebook */

#include <linux/fs.h>
+#include <linux/anon_inodes.h>
#include <linux/filter.h>
#include <linux/bpf.h>

@@ -20,12 +21,24 @@ struct bpf_iter_link {
struct bpf_iter_target_info *tinfo;
};

+struct bpf_iter_priv_data {
+ struct bpf_iter_target_info *tinfo;
+ struct bpf_prog *prog;
+ u64 session_id;
+ u64 seq_num;
+ bool done_stop;
+ u8 target_private[] __aligned(8);
+};
+
static struct list_head targets = LIST_HEAD_INIT(targets);
static DEFINE_MUTEX(targets_mutex);

/* protect bpf_iter_link changes */
static DEFINE_MUTEX(link_mutex);

+/* incremented on every opened seq_file */
+static atomic64_t session_id;
+
/* 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():
@@ -144,6 +157,33 @@ static ssize_t bpf_seq_read(struct file *file, char __user *buf, size_t size,
return copied;
}

+static int iter_release(struct inode *inode, struct file *file)
+{
+ struct bpf_iter_priv_data *iter_priv;
+ struct seq_file *seq;
+
+ seq = file->private_data;
+ if (!seq)
+ return 0;
+
+ iter_priv = container_of(seq->private, struct bpf_iter_priv_data,
+ target_private);
+
+ if (iter_priv->tinfo->fini_seq_private)
+ iter_priv->tinfo->fini_seq_private(seq->private);
+
+ bpf_prog_put(iter_priv->prog);
+ seq->private = iter_priv;
+
+ return seq_release_private(inode, file);
+}
+
+static const struct file_operations bpf_iter_fops = {
+ .llseek = no_llseek,
+ .read = bpf_seq_read,
+ .release = iter_release,
+};
+
int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
{
struct bpf_iter_target_info *tinfo;
@@ -304,3 +344,92 @@ int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)

return bpf_link_settle(&link_primer);
}
+
+static void init_seq_meta(struct bpf_iter_priv_data *priv_data,
+ struct bpf_iter_target_info *tinfo,
+ struct bpf_prog *prog)
+{
+ priv_data->tinfo = tinfo;
+ priv_data->prog = prog;
+ priv_data->session_id = atomic64_inc_return(&session_id);
+ priv_data->seq_num = 0;
+ priv_data->done_stop = false;
+}
+
+static int prepare_seq_file(struct file *file, struct bpf_iter_link *link)
+{
+ struct bpf_iter_priv_data *priv_data;
+ struct bpf_iter_target_info *tinfo;
+ struct bpf_prog *prog;
+ u32 total_priv_dsize;
+ struct seq_file *seq;
+ int err = 0;
+
+ mutex_lock(&link_mutex);
+ prog = link->link.prog;
+ bpf_prog_inc(prog);
+ mutex_unlock(&link_mutex);
+
+ tinfo = link->tinfo;
+ total_priv_dsize = offsetof(struct bpf_iter_priv_data, target_private) +
+ tinfo->seq_priv_size;
+ priv_data = __seq_open_private(file, tinfo->seq_ops, total_priv_dsize);
+ if (!priv_data) {
+ err = -ENOMEM;
+ goto release_prog;
+ }
+
+ if (tinfo->init_seq_private) {
+ err = tinfo->init_seq_private(priv_data->target_private);
+ if (err)
+ goto release_seq_file;
+ }
+
+ init_seq_meta(priv_data, tinfo, prog);
+ seq = file->private_data;
+ seq->private = priv_data->target_private;
+
+ return 0;
+
+release_seq_file:
+ seq_release_private(file->f_inode, file);
+ file->private_data = NULL;
+release_prog:
+ bpf_prog_put(prog);
+ return err;
+}
+
+int bpf_iter_new_fd(struct bpf_link *link)
+{
+ struct file *file;
+ unsigned int flags;
+ int err, fd;
+
+ if (link->ops != &bpf_iter_link_lops)
+ return -EINVAL;
+
+ flags = O_RDONLY | O_CLOEXEC;
+ fd = get_unused_fd_flags(flags);
+ if (fd < 0)
+ return fd;
+
+ file = anon_inode_getfile("bpf_iter", &bpf_iter_fops, NULL, flags);
+ if (IS_ERR(file)) {
+ err = PTR_ERR(file);
+ goto free_fd;
+ }
+
+ err = prepare_seq_file(file,
+ container_of(link, struct bpf_iter_link, link));
+ if (err)
+ goto free_file;
+
+ fd_install(fd, file);
+ return fd;
+
+free_file:
+ fput(file);
+free_fd:
+ put_unused_fd(fd);
+ return err;
+}
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6ffe2d8fb6c7..a293e88ee01a 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3941,6 +3941,29 @@ static int bpf_enable_stats(union bpf_attr *attr)
return -EINVAL;
}

+#define BPF_ITER_CREATE_LAST_FIELD iter_create.flags
+
+static int bpf_iter_create(union bpf_attr *attr)
+{
+ struct bpf_link *link;
+ int err;
+
+ if (CHECK_ATTR(BPF_ITER_CREATE))
+ return -EINVAL;
+
+ if (attr->iter_create.flags)
+ return -EINVAL;
+
+ link = bpf_link_get_from_fd(attr->iter_create.link_fd);
+ if (IS_ERR(link))
+ return PTR_ERR(link);
+
+ err = bpf_iter_new_fd(link);
+ bpf_link_put(link);
+
+ return err;
+}
+
SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
{
union bpf_attr attr;
@@ -4068,6 +4091,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
case BPF_ENABLE_STATS:
err = bpf_enable_stats(&attr);
break;
+ case BPF_ITER_CREATE:
+ err = bpf_iter_create(&attr);
+ break;
default:
err = -EINVAL;
break;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 2bf33979f9ae..97ceb0f2e539 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -116,6 +116,7 @@ enum bpf_cmd {
BPF_LINK_GET_FD_BY_ID,
BPF_LINK_GET_NEXT_ID,
BPF_ENABLE_STATS,
+ BPF_ITER_CREATE,
};

enum bpf_map_type {
@@ -614,6 +615,11 @@ union bpf_attr {
__u32 type;
} enable_stats;

+ struct { /* struct used by BPF_ITER_CREATE command */
+ __u32 link_fd;
+ __u32 flags;
+ } iter_create;
+
} __attribute__((aligned(8)));

/* The description below is an attempt at providing documentation to eBPF
--
2.24.1