bpf: add new BPF_BTF_GET_NEXT_ID syscall command

Add a new command for the bpf() system call: BPF_BTF_GET_NEXT_ID is used
to cycle through all BTF objects loaded on the system.

The motivation is to be able to inspect (list) all BTF objects presents
on the system.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

4 files changed, 10 insertions, 2 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 15ae49862b82..5b9d22338606 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -24,6 +24,9 @@ struct seq_file;
 struct btf;
 struct btf_type;
 
+extern struct idr btf_idr;
+extern spinlock_t btf_idr_lock;
+
 /* map is generic key/value storage optionally accesible by eBPF programs */
 struct bpf_map_ops {
         /* funcs callable from userspace (via syscall) */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 0ef594ac3899..8aa6126f0b6e 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -106,6 +106,7 @@ enum bpf_cmd {
         BPF_TASK_FD_QUERY,
         BPF_MAP_LOOKUP_AND_DELETE_ELEM,
         BPF_MAP_FREEZE,
+        BPF_BTF_GET_NEXT_ID,
 };
 
 enum bpf_map_type {
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 6b403dc18486..adb3adcebe3c 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -195,8 +195,8 @@
              i < btf_type_vlen(struct_type);                                    \
              i++, member++)
 
-static DEFINE_IDR(btf_idr);
-static DEFINE_SPINLOCK(btf_idr_lock);
+DEFINE_IDR(btf_idr);
+DEFINE_SPINLOCK(btf_idr_lock);
 
 struct btf {
         void *data;
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index cf8052b016e7..c0f62fd67c6b 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2884,6 +2884,10 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
                 err = bpf_obj_get_next_id(&attr, uattr,
                                           &map_idr, &map_idr_lock);
                 break;
+        case BPF_BTF_GET_NEXT_ID:
+                err = bpf_obj_get_next_id(&attr, uattr,
+                                          &btf_idr, &btf_idr_lock);
+                break;
         case BPF_PROG_GET_FD_BY_ID:
                 err = bpf_prog_get_fd_by_id(&attr);
                 break;