From: Yafang Shao laoar.shao@gmail.com
commit 1e9d74660d4df625b0889e77018f9e94727ceacd upstream.
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 environment is not matched, 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:
- kernel 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@iogearbox.net Signed-off-by: Yafang Shao laoar.shao@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Christian Brauner christian.brauner@ubuntu.com Cc: David Howells dhowells@redhat.com Cc: Al Viro viro@zeniv.linux.org.uk Link: https://lore.kernel.org/bpf/20220108134623.32467-1-laoar.shao@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/bpf/inode.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)
--- a/kernel/bpf/inode.c +++ b/kernel/bpf/inode.c @@ -648,12 +648,22 @@ static int bpf_parse_param(struct fs_con int opt;
opt = fs_parse(fc, bpf_fs_parameters, param, &result); - if (opt < 0) + if (opt < 0) { /* We might like to report bad mount options here, but * traditionally we've ignored all mount options, so we'd * better continue to ignore non-existing options for bpf. */ - return opt == -ENOPARAM ? 0 : opt; + if (opt == -ENOPARAM) { + opt = vfs_parse_fs_param_source(fc, param); + if (opt != -ENOPARAM) + return opt; + + return 0; + } + + if (opt < 0) + return opt; + }
switch (opt) { case OPT_MODE: