netdev - Re: [PATCH v2] bpf: fix mount source show for bpffs

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Date:   Mon, 10 Jan 2022 10:41:58 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     daniel@...earbox.net, ast@...nel.org, andrii@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v2] bpf: fix mount source show for bpffs

On Sat, Jan 08, 2022 at 01:46:23PM +0000, Yafang Shao wrote:
> We noticed our tc ebpf tools can't start after we upgrade our in-house
> kernel version from 4.19 to 5.10. That is because of the behaviour change
> in bpffs caused by commit
> d2935de7e4fd ("vfs: Convert bpf to use the new mount API").
> 
> In our tc ebpf tools, we do strict environment check. If the enrioment is
> not match, we won't allow to start the ebpf progs. One of the check is
> whether bpffs is properly mounted. The mount information of bpffs in
> kernel-4.19 and kernel-5.10 are as follows,
> 
> - kenrel 4.19
> $ mount -t bpf bpffs /sys/fs/bpf
> $ mount -t bpf
> bpffs on /sys/fs/bpf type bpf (rw,relatime)
> 
> - kernel 5.10
> $ mount -t bpf bpffs /sys/fs/bpf
> $ mount -t bpf
> none on /sys/fs/bpf type bpf (rw,relatime)
> 
> The device name in kernel-5.10 is displayed as none instead of bpffs,
> then our environment check fails. Currently we modify the tools to adopt to
> the kernel behaviour change, but I think we'd better change the kernel code
> to keep the behavior consistent.
> 
> After this change, the mount information will be displayed the same with
> the behavior in kernel-4.19, for example,
> 
> $ mount -t bpf bpffs /sys/fs/bpf
> $ mount -t bpf
> bpffs on /sys/fs/bpf type bpf (rw,relatime)
> 
> Fixes: d2935de7e4fd ("vfs: Convert bpf to use the new mount API")
> Suggested-by: Daniel Borkmann <daniel@...earbox.net>
> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> Cc: David Howells <dhowells@...hat.com>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> 
> ---
> v1->v2:
> use the helper vfs_parse_fs_param_source() instead of open-coded (Daniel)
> ---

Looks good,
Acked-by: Christian Brauner <christian.brauner@...ntu.com>