> On Dec 16, 2020, at 10:18 AM, Yonghong Song <y...@fb.com> wrote:
>
[...]
>> +
>> + err = bpf_iter_task_vma__load(skel);
>> + if (CHECK(err, "bpf_iter_task_vma__load", "skeleton load failed\n"))
>> + goto out;
>> +
>> + do_dummy_read(skel->progs.proc_maps);
>
> This do_dummy_read() is not needed, right?
do_dummy_read() helped me got bug in earlier version. I am planning to
change the following to do smaller reads, then do_dummy_read() is no longer
needed.
[...]
>
>> +
>> +SEC("iter.s/task_vma") int proc_maps(struct bpf_iter__task_vma *ctx)
>> +{
>> + struct __vm_area_struct *vma = ctx->vma;
>> + struct seq_file *seq = ctx->meta->seq;
>> + struct task_struct *task = ctx->task;
>> + struct file *file = ctx->file;
>> + char perm_str[] = "----";
>> +
>> + if (task == (void *)0 || vma == (void *)0 || task->pid != pid)
>
> I suppose kernel already filtered all non-group-leader tasks, so here
> we can have task->tgid != pid?
Yeah, that works.
>
>> + return 0;
>
> Using /proc system, user typically do cat /proc/pid/maps. How can we
> have a similar user experience with vma_iter here? One way to do this
> is:
> - We still have this bpf program, filtering based on user pid,
> - normal bpftool iter pin command pid the program to say
> /sys/fs/bpf/task_vma
> - since "pid" is in a map, user can use bpftool to update "pid"
> with the target pid.
> - "cat /sys/fs/bpf/task_vma" will work.
>
> One thing here is pid and d_path_buf are global (map) variables, so
> if two users are trying to do "cat /sys/fs/bpf/task_vma" at the same
> time, there will be interferences and it will not work.
>
> One possible way is during BPF_ITER_CREATE, we duplicate all program
> maps. But this is unnecessary as in most cases, the bpf_iter is not
> pinned and private to applications.
>
> Any other ideas?
Maybe we can use task local storage for pid and d_path_buf?
To make it more practical, we probably want in kernel filtering based
on pid. IOW, let user specify which task to iterate.
Thanks,
Song
