Hello Tejun, On Tue, May 10, 2022 at 11:54 AM Tejun Heo <tj@xxxxxxxxxx> wrote: > > Hello, > > On Tue, May 10, 2022 at 12:18:06AM +0000, Yosry Ahmed wrote: > > From: Hao Luo <haoluo@xxxxxxxxxx> > > > > Introduce a new type of iter prog: cgroup. Unlike other bpf_iter, this > > iter doesn't iterate a set of kernel objects. Instead, it is supposed to > > be parameterized by a cgroup id and prints only that cgroup. So one > > needs to specify a target cgroup id when attaching this iter. The target > > cgroup's state can be read out via a link of this iter. > > Is there a reason why this can't be a proper iterator which supports > lseek64() to locate a specific cgroup? > There are two reasons: - Bpf_iter assumes no_llseek. I haven't looked closely on why this is so and whether we can add its support. - Second, the name 'iter' in this patch is misleading. What this patch really does is reusing the functionality of dumping in bpf_iter. 'Dumper' is a better name. We want to create one file in bpffs for each cgroup. We are essentially just iterating a set of one single element. > Thanks. > > -- > tejun
