linux-kernel - [RFC PATCH v3 10/37] fuse-bpf: Don't support export

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Date:   Mon, 17 Apr 2023 18:40:10 -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>, Yonghong Song <yhs@...com>,
        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>, kernel-team@...roid.com,
        Daniel Rosenberg <drosen@...gle.com>
Subject: [RFC PATCH v3 10/37] 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 b71e8758fab5..fe80984f099a 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1107,6 +1107,14 @@ 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;
-- 
2.40.0.634.g4ca3ef3211-goog