2019-08-20 15:36 UTC+0200 ~ Daniel Borkmann [off-list ref]

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

quoted

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 <redacted>
Reviewed-by: Jakub Kicinski <redacted>
---
  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.

No, I don't have one for data_size to be honest. I'll respin with btf_id
only then.

Thanks,
Quentin