Re: [RFC PATCH bpf-next 03/16] bpf: provide a way for targets to register themselves

Andrii Nakryiko
2020-04-10T22:25:31Z

On Wed, Apr 8, 2020 at 4:26 PM Yonghong Song <yhs@fb.com> wrote:
>
> Here, the target refers to a particular data structure
> inside the kernel we want to dump. For example, it
> can be all task_structs in the current pid namespace,
> or it could be all open files for all task_structs
> in the current pid namespace.
>
> Each target is identified with the following information:
> target_rel_path <=== relative path to /sys/kernel/bpfdump
> target_proto <=== kernel func proto which represents
> bpf program signature for this target
> seq_ops <=== seq_ops for seq_file operations
> seq_priv_size <=== seq_file private data size
> target_feature <=== target specific feature which needs
> handling outside seq_ops.
>
> The target relative path is a relative directory to /sys/kernel/bpfdump/.
> For example, it could be:
> task <=== all tasks
> task/file <=== all open files under all tasks
> ipv6_route <=== all ipv6_routes
> tcp6/sk_local_storage <=== all tcp6 socket local storages
> foo/bar/tar <=== all tar's in bar in foo
>
> The "target_feature" is mostly used for reusing existing seq_ops.
> For example, for /proc/net/<> stats, the "net" namespace is often
> stored in file private data. The target_feature enables bpf based
> dumper to set "net" properly for itself before calling shared
> seq_ops.
>
> bpf_dump_reg_target() is implemented so targets
> can register themselves. Currently, module is not
> supported, so there is no bpf_dump_unreg_target().
> The main reason is that BTF is not available for modules
> yet.
>
> Since target might call bpf_dump_reg_target() before
> bpfdump mount point is created, __bpfdump_init()
> may be called in bpf_dump_reg_target() as well.
>
> The file-based dumpers will be regular files under
> the specific target directory. For example,
> task/my1 <=== dumper "my1" iterates through all tasks
> task/file/my2 <=== dumper "my2" iterates through all open files
> under all tasks
>
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---
> include/linux/bpf.h | 4 +
> kernel/bpf/dump.c | 190 +++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 193 insertions(+), 1 deletion(-)
>

[...]

> +
> +static int dumper_unlink(struct inode *dir, struct dentry *dentry)
> +{
> + kfree(d_inode(dentry)->i_private);
> + return simple_unlink(dir, dentry);
> +}
> +
> +static const struct inode_operations bpf_dir_iops = {

noticed this reading next patch. It should probably be called
bpfdump_dir_iops to avoid confusion with bpf_dir_iops of BPF FS in
kernel/bpf/inode.c?

> + .lookup = simple_lookup,
> + .unlink = dumper_unlink,
> +};
> + …