Re: [PATCH bpf-next 1/2] bpf: enable the "open" operator on a pinned path of a struct_osp link.

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On 4/16/24 5:25 PM, Kui-Feng Lee wrote:
+int bpffs_struct_ops_link_open(struct inode *inode, struct file *filp)
+{
+	struct bpf_struct_ops_link *link = inode->i_private;
+
+	/* Paired with bpf_link_put_direct() in bpf_link_release(). */
+	bpf_link_inc(&link->link);
+	filp->private_data = link;
+	return 0;
+}
diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index af5d2ffadd70..b020d761ab0a 100644
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -360,11 +360,16 @@ static int bpf_mkmap(struct dentry *dentry, umode_t mode, void *arg)
static int bpf_mklink(struct dentry *dentry, umode_t mode, void *arg)
  {
+	const struct file_operations *fops;
  	struct bpf_link *link = arg;
- return bpf_mkobj_ops(dentry, mode, arg, &bpf_link_iops,
-			     bpf_link_is_iter(link) ?
-			     &bpf_iter_fops : &bpffs_obj_fops);
+	if (bpf_link_is_iter(link))
+		fops = &bpf_iter_fops;
+	else if (link->type == BPF_LINK_TYPE_STRUCT_OPS)

Open a pinned link and then update should not be specific to struct_ops link. e.g. should be useful to the cgroup link also?

Andrii, wdyt about supporting other link types also?

+		fops = &bpf_link_fops;
+	else
+		fops = &bpffs_obj_fops;
+	return bpf_mkobj_ops(dentry, mode, arg, &bpf_link_iops, fops);
  }
static struct dentry *
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 7d392ec83655..f66bc6215faa 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3108,7 +3108,19 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp)
  }
  #endif
-static const struct file_operations bpf_link_fops = {
+/* Support opening pinned links */
+static int bpf_link_open(struct inode *inode, struct file *filp)
+{
+	struct bpf_link *link = inode->i_private;
+
+	if (link->type == BPF_LINK_TYPE_STRUCT_OPS)
+		return bpffs_struct_ops_link_open(inode, filp);
+
+	return -EOPNOTSUPP;
+}
+
+const struct file_operations bpf_link_fops = {
+	.open = bpf_link_open,
  #ifdef CONFIG_PROC_FS
  	.show_fdinfo	= bpf_link_show_fdinfo,
  #endif





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