From: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Date: Thu, 17 Mar 2022 17:29:43 +0530
Subject: bpf: Factor out fd returning from bpf_btf_find_by_name_kind
Patch-mainline: v5.18-rc1
Git-commit: edc3ec09ab706c45e955f7a52f0904b4ed649ca9
References: jsc#PED-1377

In next few patches, we need a helper that searches all kernel BTFs
(vmlinux and module BTFs), and finds the type denoted by 'name' and
'kind'. Turns out bpf_btf_find_by_name_kind already does the same thing,
but it instead returns a BTF ID and optionally fd (if module BTF). This
is used for relocating ksyms in BPF loader code (bpftool gen skel -L).

We extract the core code out into a new helper bpf_find_btf_id, which
returns the BTF ID in the return value, and BTF pointer in an out
parameter. The reference for the returned BTF pointer is always raised,
hence user must either transfer it (e.g. to a fd), or release it after
use.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220317115957.3193097-2-memxor@gmail.com
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 kernel/bpf/btf.c |   90 ++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 53 insertions(+), 37 deletions(-)

--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -525,6 +525,48 @@ s32 btf_find_by_name_kind(const struct b
 	return -ENOENT;
 }
 
+static s32 bpf_find_btf_id(const char *name, u32 kind, struct btf **btf_p)
+{
+	struct btf *btf;
+	s32 ret;
+	int id;
+
+	btf = bpf_get_btf_vmlinux();
+	if (IS_ERR(btf))
+		return PTR_ERR(btf);
+
+	ret = btf_find_by_name_kind(btf, name, kind);
+	/* ret is never zero, since btf_find_by_name_kind returns
+	 * positive btf_id or negative error.
+	 */
+	if (ret > 0) {
+		btf_get(btf);
+		*btf_p = btf;
+		return ret;
+	}
+
+	/* If name is not found in vmlinux's BTF then search in module's BTFs */
+	spin_lock_bh(&btf_idr_lock);
+	idr_for_each_entry(&btf_idr, btf, id) {
+		if (!btf_is_module(btf))
+			continue;
+		/* linear search could be slow hence unlock/lock
+		 * the IDR to avoiding holding it for too long
+		 */
+		btf_get(btf);
+		spin_unlock_bh(&btf_idr_lock);
+		ret = btf_find_by_name_kind(btf, name, kind);
+		if (ret > 0) {
+			*btf_p = btf;
+			return ret;
+		}
+		spin_lock_bh(&btf_idr_lock);
+		btf_put(btf);
+	}
+	spin_unlock_bh(&btf_idr_lock);
+	return ret;
+}
+
 const struct btf_type *btf_type_skip_modifiers(const struct btf *btf,
 					       u32 id, u32 *res_id)
 {
@@ -6562,7 +6604,8 @@ static struct btf *btf_get_module_btf(co
 
 BPF_CALL_4(bpf_btf_find_by_name_kind, char *, name, int, name_sz, u32, kind, int, flags)
 {
-	struct btf *btf;
+	struct btf *btf = NULL;
+	int btf_obj_fd = 0;
 	long ret;
 
 	if (flags)
@@ -6571,44 +6614,17 @@ BPF_CALL_4(bpf_btf_find_by_name_kind, ch
 	if (name_sz <= 1 || name[name_sz - 1])
 		return -EINVAL;
 
-	btf = bpf_get_btf_vmlinux();
-	if (IS_ERR(btf))
-		return PTR_ERR(btf);
-
-	ret = btf_find_by_name_kind(btf, name, kind);
-	/* ret is never zero, since btf_find_by_name_kind returns
-	 * positive btf_id or negative error.
-	 */
-	if (ret < 0) {
-		struct btf *mod_btf;
-		int id;
-
-		/* If name is not found in vmlinux's BTF then search in module's BTFs */
-		spin_lock_bh(&btf_idr_lock);
-		idr_for_each_entry(&btf_idr, mod_btf, id) {
-			if (!btf_is_module(mod_btf))
-				continue;
-			/* linear search could be slow hence unlock/lock
-			 * the IDR to avoiding holding it for too long
-			 */
-			btf_get(mod_btf);
-			spin_unlock_bh(&btf_idr_lock);
-			ret = btf_find_by_name_kind(mod_btf, name, kind);
-			if (ret > 0) {
-				int btf_obj_fd;
-
-				btf_obj_fd = __btf_new_fd(mod_btf);
-				if (btf_obj_fd < 0) {
-					btf_put(mod_btf);
-					return btf_obj_fd;
-				}
-				return ret | (((u64)btf_obj_fd) << 32);
-			}
-			spin_lock_bh(&btf_idr_lock);
-			btf_put(mod_btf);
+	ret = bpf_find_btf_id(name, kind, &btf);
+	if (ret > 0 && btf_is_module(btf)) {
+		btf_obj_fd = __btf_new_fd(btf);
+		if (btf_obj_fd < 0) {
+			btf_put(btf);
+			return btf_obj_fd;
 		}
-		spin_unlock_bh(&btf_idr_lock);
+		return ret | (((u64)btf_obj_fd) << 32);
 	}
+	if (ret > 0)
+		btf_put(btf);
 	return ret;
 }