[PATCH bpf-next v3 07/21] bpf: create file bpf iterator

[Yonghong Song <yhs@xxxxxx>]

To produce a file bpf iterator, the fd must be
corresponding to a link_fd assocciated with a
trace/iter program. When the pinned file is
opened, a seq_file will be generated.

Acked-by: Andrii Nakryiko <andriin@xxxxxx>
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
 include/linux/bpf.h   |  2 ++
 kernel/bpf/bpf_iter.c | 17 ++++++++++++++++-
 kernel/bpf/inode.c    |  5 ++++-
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 80b1b9d8a638..b06653ab3476 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1022,6 +1022,7 @@ static inline void bpf_enable_instrumentation(void)
 
 extern const struct file_operations bpf_map_fops;
 extern const struct file_operations bpf_prog_fops;
+extern const struct file_operations bpf_iter_fops;
 
 #define BPF_PROG_TYPE(_id, _name, prog_ctx_type, kern_ctx_type) \
 	extern const struct bpf_prog_ops _name ## _prog_ops; \
@@ -1145,6 +1146,7 @@ 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);
 
 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 917df4c69966..b0b8726c08f8 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -39,6 +39,8 @@ static DEFINE_MUTEX(link_mutex);
 /* incremented on every opened seq_file */
 static atomic64_t session_id;
 
+static int prepare_seq_file(struct file *file, struct bpf_iter_link *link);
+
 /* 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():
@@ -157,6 +159,13 @@ static ssize_t bpf_seq_read(struct file *file, char __user *buf, size_t size,
 	return copied;
 }
 
+static int iter_open(struct inode *inode, struct file *file)
+{
+	struct bpf_iter_link *link = inode->i_private;
+
+	return prepare_seq_file(file, link);
+}
+
 static int iter_release(struct inode *inode, struct file *file)
 {
 	struct bpf_iter_priv_data *iter_priv;
@@ -178,7 +187,8 @@ static int iter_release(struct inode *inode, struct file *file)
 	return seq_release_private(inode, file);
 }
 
-static const struct file_operations bpf_iter_fops = {
+const struct file_operations bpf_iter_fops = {
+	.open		= iter_open,
 	.llseek		= no_llseek,
 	.read		= bpf_seq_read,
 	.release	= iter_release,
@@ -305,6 +315,11 @@ static const struct bpf_link_ops bpf_iter_link_lops = {
 	.update_prog = bpf_iter_link_replace,
 };
 
+bool bpf_link_is_iter(struct bpf_link *link)
+{
+	return link->ops == &bpf_iter_link_lops;
+}
+
 int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 {
 	struct bpf_link_primer link_primer;
diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index 95087d9f4ed3..fb878ba3f22f 100644
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -358,8 +358,11 @@ static int bpf_mkmap(struct dentry *dentry, umode_t mode, void *arg)
 
 static int bpf_mklink(struct dentry *dentry, umode_t mode, void *arg)
 {
+	struct bpf_link *link = arg;
+
 	return bpf_mkobj_ops(dentry, mode, arg, &bpf_link_iops,
-			     &bpffs_obj_fops);
+			     bpf_link_is_iter(link) ?
+			     &bpf_iter_fops : &bpffs_obj_fops);
 }
 
 static struct dentry *
-- 
2.24.1