bpf: Implement link_query for bpf iterators

This patch implemented bpf_link callback functions
show_fdinfo and fill_link_info to support link_query
interface.

The general interface for show_fdinfo and fill_link_info
will print/fill the target_name. Each targets can
register show_fdinfo and fill_link_info callbacks
to print/fill more target specific information.

For example, the below is a fdinfo result for a bpf
task iterator.
  $ cat /proc/1749/fdinfo/7
  pos:    0
  flags:  02000000
  mnt_id: 14
  link_type:      iter
  link_id:        11
  prog_tag:       990e1f8152f7e54f
  prog_id:        59
  target_name:    task

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200821184418.574122-1-yhs@fb.com

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a9b7185..529e9b1 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1218,12 +1218,18 @@ typedef int (*bpf_iter_attach_target_t)(struct bpf_prog *prog,
                                        union bpf_iter_link_info *linfo,
                                        struct bpf_iter_aux_info *aux);
 typedef void (*bpf_iter_detach_target_t)(struct bpf_iter_aux_info *aux);
+typedef void (*bpf_iter_show_fdinfo_t) (const struct bpf_iter_aux_info *aux,
+                                       struct seq_file *seq);
+typedef int (*bpf_iter_fill_link_info_t)(const struct bpf_iter_aux_info *aux,
+                                        struct bpf_link_info *info);
 
 #define BPF_ITER_CTX_ARG_MAX 2
 struct bpf_iter_reg {
        const char *target;
        bpf_iter_attach_target_t attach_target;
        bpf_iter_detach_target_t detach_target;
+       bpf_iter_show_fdinfo_t show_fdinfo;
+       bpf_iter_fill_link_info_t fill_link_info;
        u32 ctx_arg_info_size;
        struct bpf_ctx_arg_aux ctx_arg_info[BPF_ITER_CTX_ARG_MAX];
        const struct bpf_iter_seq_info *seq_info;

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 0480f89..a1bbaff 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4071,6 +4071,13 @@ struct bpf_link_info {
                        __u64 cgroup_id;
                        __u32 attach_type;
                } cgroup;
+               struct {
+                       __aligned_u64 target_name; /* in/out: target_name buffer ptr */
+                       __u32 target_name_len;     /* in/out: target_name buffer len */
+                       union {
+                               __u32 map_id;
+                       } map;
+               } iter;
                struct  {
                        __u32 netns_ino;
                        __u32 attach_type;

diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index b671596..aeec7e1 100644 (file)
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -377,10 +377,68 @@ out_unlock:
        return ret;
 }
 
+static void bpf_iter_link_show_fdinfo(const struct bpf_link *link,
+                                     struct seq_file *seq)
+{
+       struct bpf_iter_link *iter_link =
+               container_of(link, struct bpf_iter_link, link);
+       bpf_iter_show_fdinfo_t show_fdinfo;
+
+       seq_printf(seq,
+                  "target_name:\t%s\n",
+                  iter_link->tinfo->reg_info->target);
+
+       show_fdinfo = iter_link->tinfo->reg_info->show_fdinfo;
+       if (show_fdinfo)
+               show_fdinfo(&iter_link->aux, seq);
+}
+
+static int bpf_iter_link_fill_link_info(const struct bpf_link *link,
+                                       struct bpf_link_info *info)
+{
+       struct bpf_iter_link *iter_link =
+               container_of(link, struct bpf_iter_link, link);
+       char __user *ubuf = u64_to_user_ptr(info->iter.target_name);
+       bpf_iter_fill_link_info_t fill_link_info;
+       u32 ulen = info->iter.target_name_len;
+       const char *target_name;
+       u32 target_len;
+
+       if (!ulen ^ !ubuf)
+               return -EINVAL;
+
+       target_name = iter_link->tinfo->reg_info->target;
+       target_len =  strlen(target_name);
+       info->iter.target_name_len = target_len + 1;
+
+       if (ubuf) {
+               if (ulen >= target_len + 1) {
+                       if (copy_to_user(ubuf, target_name, target_len + 1))
+                               return -EFAULT;
+               } else {
+                       char zero = '\0';
+
+                       if (copy_to_user(ubuf, target_name, ulen - 1))
+                               return -EFAULT;
+                       if (put_user(zero, ubuf + ulen - 1))
+                               return -EFAULT;
+                       return -ENOSPC;
+               }
+       }
+
+       fill_link_info = iter_link->tinfo->reg_info->fill_link_info;
+       if (fill_link_info)
+               return fill_link_info(&iter_link->aux, info);
+
+       return 0;
+}
+
 static const struct bpf_link_ops bpf_iter_link_lops = {
        .release = bpf_iter_link_release,
        .dealloc = bpf_iter_link_dealloc,
        .update_prog = bpf_iter_link_replace,
+       .show_fdinfo = bpf_iter_link_show_fdinfo,
+       .fill_link_info = bpf_iter_link_fill_link_info,
 };
 
 bool bpf_link_is_iter(struct bpf_link *link)

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 0480f89..a1bbaff 100644 (file)
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4071,6 +4071,13 @@ struct bpf_link_info {
                        __u64 cgroup_id;
                        __u32 attach_type;
                } cgroup;
+               struct {
+                       __aligned_u64 target_name; /* in/out: target_name buffer ptr */
+                       __u32 target_name_len;     /* in/out: target_name buffer len */
+                       union {
+                               __u32 map_id;
+                       } map;
+               } iter;
                struct  {
                        __u32 netns_ino;
                        __u32 attach_type;