bpf: Create file bpf iterator

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.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200509175906.2475893-1-yhs@fb.com

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 80b1b9d8a6389379a84ce8ed21e0b642bbe17389..b06653ab34769df0e4f26edd17d78b42e55a9a50 100644 (file)
--- 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 e7129b57865f330f7fbac9bcb2818dc7adb1d62f..090f09b0eacbdbf8894a96456552cc0ef80cbf41 100644 (file)
--- 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():
@@ -162,6 +164,13 @@ done:
        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;
@@ -183,7 +192,8 @@ 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,
@@ -310,6 +320,11 @@ 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 95087d9f4ed3eeef412a4b8aeeabcc93b5341348..fb878ba3f22f030efbbc9e1f3949443f6ad53337 100644 (file)
--- 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 *