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bpf: Introduce cgroup iter

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Cgroup_iter is a type of bpf_iter. It walks over cgroups in four modes:

 - walking a cgroup's descendants in pre-order.
 - walking a cgroup's descendants in post-order.
 - walking a cgroup's ancestors.
 - process only the given cgroup.

When attaching cgroup_iter, one can set a cgroup to the iter_link
created from attaching. This cgroup is passed as a file descriptor
or cgroup id and serves as the starting point of the walk. If no
cgroup is specified, the starting point will be the root cgroup v2.

For walking descendants, one can specify the order: either pre-order or
post-order. For walking ancestors, the walk starts at the specified
cgroup and ends at the root.

One can also terminate the walk early by returning 1 from the iter
program.

Note that because walking cgroup hierarchy holds cgroup_mutex, the iter
program is called with cgroup_mutex held.

Currently only one session is supported, which means, depending on the
volume of data bpf program intends to send to user space, the number
of cgroups that can be walked is limited. For example, given the current
buffer size is 8 * PAGE_SIZE, if the program sends 64B data for each
cgroup, assuming PAGE_SIZE is 4kb, the total number of cgroups that can
be walked is 512. This is a limitation of cgroup_iter. If the output
data is larger than the kernel buffer size, after all data in the
kernel buffer is consumed by user space, the subsequent read() syscall
will signal EOPNOTSUPP. In order to work around, the user may have to
update their program to reduce the volume of data sent to output. For
example, skip some uninteresting cgroups. In future, we may extend
bpf_iter flags to allow customizing buffer size.

Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Hao Luo <haoluo@google.com>
Link: https://lore.kernel.org/r/20220824233117.1312810-2-haoluo@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Hao Luo
2022-08-24 16:31:13 -07:00
committed by Alexei Starovoitov
parent 7e165d1939
commit d4ccaf58a8
6 changed files with 357 additions and 2 deletions
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8
include/linux/bpf.h
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@@ -48,6 +48,7 @@ struct mem_cgroup;
struct module;
struct bpf_func_state;
struct ftrace_ops;
struct cgroup;
extern struct idr btf_idr;
extern spinlock_t btf_idr_lock;
@@ -1730,7 +1731,14 @@ int bpf_obj_get_user(const char __user *pathname, int flags);
int __init bpf_iter_ ## target(args) { return 0; }
struct bpf_iter_aux_info {
/* for map_elem iter */
struct bpf_map *map;
/* for cgroup iter */
struct {
struct cgroup *start; /* starting cgroup */
enum bpf_cgroup_iter_order order;
} cgroup;
};
typedef int (*bpf_iter_attach_target_t)(struct bpf_prog *prog,