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

[Yonghong Song <yhs@fb.com>]

On 4/10/20 3:25 PM, Andrii Nakryiko wrote:
> 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?

make sense. originally probably copied from inode.c and did not
change that.

> 
>> +       .lookup         = simple_lookup,
>> +       .unlink         = dumper_unlink,
>> +};
>> +
> 
> [...]
>