linux-kernel - [RFC PATCH v4 06/36] fuse-bpf: Don't support export

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Date: Thu, 28 Mar 2024 18:53:21 -0700
From: Daniel Rosenberg <drosen@...gle.com>
To: Miklos Szeredi <miklos@...redi.hu>, bpf@...r.kernel.org, 
	Alexei Starovoitov <ast@...nel.org>
Cc: Amir Goldstein <amir73il@...il.com>, linux-kernel@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-unionfs@...r.kernel.org, 
	Daniel Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Eduard Zingerman <eddyz87@...il.com>, Yonghong Song <yonghong.song@...ux.dev>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>, Jonathan Corbet <corbet@....net>, 
	Joanne Koong <joannelkoong@...il.com>, Mykola Lysenko <mykolal@...com>, 
	Christian Brauner <brauner@...nel.org>, kernel-team@...roid.com, 
	Daniel Rosenberg <drosen@...gle.com>
Subject: [RFC PATCH v4 06/36] fuse-bpf: Don't support export_operations

In the future, we may choose to support these, but it poses some
challenges. In order to create a disconnected dentry/inode, we'll need
to encode the mountpoint and bpf into the file_handle, which means we'd
need a stable representation of them. This also won't hold up to cases
where the bpf is not stateless. One possibility is registering bpf
programs and mounts in a specific order, so they can be assigned
consistent ids we can use in the file_handle. We can defer to the lower
filesystem for the lower inode's representation in the file_handle.

Signed-off-by: Daniel Rosenberg <drosen@...gle.com>
---
 fs/fuse/inode.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 6570fe7a9b53..b47b2e41e5e4 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1187,6 +1187,14 @@ static int fuse_encode_fh(struct inode *inode, u32 *fh, int *max_len,
 	nodeid = get_fuse_inode(inode)->nodeid;
 	generation = inode->i_generation;
 
+#ifdef CONFIG_FUSE_BPF
+	/* TODO: Does it make sense to support this in some cases? */
+	if (!nodeid && get_fuse_inode(inode)->backing_inode) {
+		*max_len = 0;
+		return FILEID_INVALID;
+	}
+#endif
+
 	fh[0] = (u32)(nodeid >> 32);
 	fh[1] = (u32)(nodeid & 0xffffffff);
 	fh[2] = generation;
-- 
2.44.0.478.gd926399ef9-goog