Re: [PATCH bpf-next] bpf: add BTF ids in procfs for file descriptors to BTF objects

[Daniel Borkmann]

On 8/20/19 11:52 AM, Quentin Monnet wrote:

Implement the show_fdinfo hook for BTF FDs file operations, and make it
print the id and the size of the BTF object. This allows for a quick
retrieval of the BTF id from its FD; or it can help understanding what
type of object (BTF) the file descriptor points to.

Signed-off-by: Quentin Monnet <quentin.mon...@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicin...@netronome.com>
---
  kernel/bpf/btf.c | 16 ++++++++++++++++
  1 file changed, 16 insertions(+)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 5fcc7a17eb5a..39e184f1b27c 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3376,6 +3376,19 @@ void btf_type_seq_show(const struct btf *btf, u32 
type_id, void *obj,
        btf_type_ops(t)->seq_show(btf, t, type_id, obj, 0, m);
  }

+#ifdef CONFIG_PROC_FS

+static void bpf_btf_show_fdinfo(struct seq_file *m, struct file *filp)
+{
+       const struct btf *btf = filp->private_data;
+
+       seq_printf(m,
+                  "btf_id:\t%u\n"
+                  "data_size:\t%u\n",
+                  btf->id,
+                  btf->data_size);

Looks good, exposing btf_id makes sense to me in order to correlate with 
applications.
Do you have a concrete use case for data_size to expose it this way as opposed 
to fetch
it via btf_get_info_by_fd()? If not, I'd say lets only add btf_id in there.

+}
+#endif
+
  static int btf_release(struct inode *inode, struct file *filp)
  {
        btf_put(filp->private_data);
@@ -3383,6 +3396,9 @@ static int btf_release(struct inode *inode, struct file 
*filp)
  }

const struct file_operations btf_fops = {

+#ifdef CONFIG_PROC_FS
+       .show_fdinfo    = bpf_btf_show_fdinfo,
+#endif
        .release        = btf_release,
  };

Thanks,
Daniel