Messages in this thread | | | Date | Wed, 27 Jul 2022 22:49:01 -0700 | Subject | Re: [PATCH bpf-next v5 4/8] bpf: Introduce cgroup iter | From | Yonghong Song <> |
| |
On 7/22/22 10:48 AM, Yosry Ahmed wrote: > From: Hao Luo <haoluo@google.com> > > Cgroup_iter is a type of bpf_iter. It walks over cgroups in three modes: > > - walking a cgroup's descendants in pre-order. > - walking a cgroup's descendants in post-order. > - walking a cgroup's ancestors. > > When attaching cgroup_iter, one can set a cgroup to the iter_link > created from attaching. This cgroup is passed as a file descriptor and > serves as the starting point of the walk. If no cgroup is specified, > the starting point will be the root cgroup. > > 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, the total number of cgroups that can be walked is 512. This is
PAGE_SIZE needs to be 4KB in order to conclude that the total number of walked cgroups is 512.
> a limitation of cgroup_iter. If the output data is larger than the > buffer size, the second read() 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. > > Signed-off-by: Hao Luo <haoluo@google.com> > Signed-off-by: Yosry Ahmed <yosryahmed@google.com> > Acked-by: Yonghong Song <yhs@fb.com> > --- > include/linux/bpf.h | 8 + > include/uapi/linux/bpf.h | 30 +++ > kernel/bpf/Makefile | 3 + > kernel/bpf/cgroup_iter.c | 252 ++++++++++++++++++ > tools/include/uapi/linux/bpf.h | 30 +++ > .../selftests/bpf/prog_tests/btf_dump.c | 4 +- > 6 files changed, 325 insertions(+), 2 deletions(-) > create mode 100644 kernel/bpf/cgroup_iter.c
This patch cannot apply to bpf-next cleanly, so please rebase and post again.
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index a97751d845c9..9061618fe929 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -47,6 +47,7 @@ struct kobject; > struct mem_cgroup; > struct module; > struct bpf_func_state; > +struct cgroup; > > extern struct idr btf_idr; > extern spinlock_t btf_idr_lock; > @@ -1717,7 +1718,14 @@ 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 */ > + int order; > + } cgroup; > }; > > typedef int (*bpf_iter_attach_target_t)(struct bpf_prog *prog, > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > index ffcbf79a556b..fe50c2489350 100644 > --- a/include/uapi/linux/bpf.h > +++ b/include/uapi/linux/bpf.h > @@ -87,10 +87,30 @@ struct bpf_cgroup_storage_key { > __u32 attach_type; /* program attach type (enum bpf_attach_type) */ > }; > > +enum bpf_iter_cgroup_traversal_order { > + BPF_ITER_CGROUP_PRE = 0, /* pre-order traversal */ > + BPF_ITER_CGROUP_POST, /* post-order traversal */ > + BPF_ITER_CGROUP_PARENT_UP, /* traversal of ancestors up to the root */ > +}; > + > union bpf_iter_link_info { > struct { > __u32 map_fd; > } map; > + > + /* cgroup_iter walks either the live descendants of a cgroup subtree, or the > + * ancestors of a given cgroup. > + */ > + struct { > + /* Cgroup file descriptor. This is root of the subtree if walking > + * descendants; it's the starting cgroup if walking the ancestors. > + * If it is left 0, the traversal starts from the default cgroup v2 > + * root. For walking v1 hierarchy, one should always explicitly > + * specify the cgroup_fd. > + */
I did see how the above cgroup v1/v2 scenarios are enforced.
> + __u32 cgroup_fd; > + __u32 traversal_order; > + } cgroup; > }; > > /* BPF syscall commands, see bpf(2) man-page for more details. */ > @@ -6136,6 +6156,16 @@ struct bpf_link_info { > __u32 map_id; > } map; > }; > + union { > + struct { > + __u64 cgroup_id; > + __u32 traversal_order; > + } cgroup; > + }; > + /* For new iters, if the first field is larger than __u32, > + * the struct should be added in the second union. Otherwise, > + * it will create holes before map_id, breaking uapi. > + */
Please put the comment above the union. Let us just say, if the iter specific field is __u32, it can be put in the first or second union. Otherwise, it is put in second union.
> } iter; > struct { > __u32 netns_ino; > diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile > index 057ba8e01e70..00e05b69a4df 100644 > --- a/kernel/bpf/Makefile > +++ b/kernel/bpf/Makefile > @@ -24,6 +24,9 @@ endif > ifeq ($(CONFIG_PERF_EVENTS),y) > obj-$(CONFIG_BPF_SYSCALL) += stackmap.o > endif > +ifeq ($(CONFIG_CGROUPS),y) > +obj-$(CONFIG_BPF_SYSCALL) += cgroup_iter.o > +endif > obj-$(CONFIG_CGROUP_BPF) += cgroup.o > ifeq ($(CONFIG_INET),y) > obj-$(CONFIG_BPF_SYSCALL) += reuseport_array.o > diff --git a/kernel/bpf/cgroup_iter.c b/kernel/bpf/cgroup_iter.c > new file mode 100644 > index 000000000000..1027faed0b8b > --- /dev/null > +++ b/kernel/bpf/cgroup_iter.c > @@ -0,0 +1,252 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/* Copyright (c) 2022 Google */ > +#include <linux/bpf.h> > +#include <linux/btf_ids.h> > +#include <linux/cgroup.h> > +#include <linux/kernel.h> > +#include <linux/seq_file.h> > + > +#include "../cgroup/cgroup-internal.h" /* cgroup_mutex and cgroup_is_dead */ > + > +/* cgroup_iter provides three modes of traversal to the cgroup hierarchy. > + * > + * 1. Walk the descendants of a cgroup in pre-order. > + * 2. Walk the descendants of a cgroup in post-order. > + * 2. Walk the ancestors of a cgroup. > + * > + * For walking descendants, cgroup_iter can walk in either pre-order or > + * post-order. For walking ancestors, the iter walks up from a cgroup to > + * the root. > + * > + * The iter program can terminate the walk early by returning 1. Walk > + * continues if prog returns 0. > + * > + * The prog can check (seq->num == 0) to determine whether this is > + * the first element. The prog may also be passed a NULL cgroup, > + * which means the walk has completed and the prog has a chance to > + * do post-processing, such as outputing an epilogue. > + * > + * Note: the iter_prog 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, the total number of cgroups that can be walked is 512. This is
Again, let us specify PAGE_SIZE = 4KB here.
> + * a limitation of cgroup_iter. If the output data is larger than the > + * buffer size, the second read() 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. > + */ > + > +struct bpf_iter__cgroup { > + __bpf_md_ptr(struct bpf_iter_meta *, meta); > + __bpf_md_ptr(struct cgroup *, cgroup); > +}; > + > +struct cgroup_iter_priv { > + struct cgroup_subsys_state *start_css; > + bool terminate; > + int order; > +}; > + > +static void *cgroup_iter_seq_start(struct seq_file *seq, loff_t *pos) > +{ > + struct cgroup_iter_priv *p = seq->private; > + > + mutex_lock(&cgroup_mutex); > + > + /* cgroup_iter doesn't support read across multiple sessions. */ > + if (*pos > 0) > + return ERR_PTR(-EOPNOTSUPP);
This is not quite right. Let us say, the number of cgroups is 1, after bpf program run, pos = 1, and the control return to user space. Now the second read() will return -EOPNOTSUPP which is not right. -EOPNOTSUPP should be returned ONLY if the previous cgroup iterations do not traverse all cgroups. So you might need to record additional information in cgroup_iter_priv to record such information.
> + > + ++*pos; > + p->terminate = false; > + if (p->order == BPF_ITER_CGROUP_PRE) > + return css_next_descendant_pre(NULL, p->start_css); > + else if (p->order == BPF_ITER_CGROUP_POST) > + return css_next_descendant_post(NULL, p->start_css); > + else /* BPF_ITER_CGROUP_PARENT_UP */ > + return p->start_css; > +} > + > +static int __cgroup_iter_seq_show(struct seq_file *seq, > + struct cgroup_subsys_state *css, int in_stop); > + > +static void cgroup_iter_seq_stop(struct seq_file *seq, void *v) > +{ > + /* pass NULL to the prog for post-processing */ > + if (!v) > + __cgroup_iter_seq_show(seq, NULL, true); > + mutex_unlock(&cgroup_mutex); > +} > + > +static void *cgroup_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos) > +{ > + struct cgroup_subsys_state *curr = (struct cgroup_subsys_state *)v; > + struct cgroup_iter_priv *p = seq->private; > + > + ++*pos; > + if (p->terminate) > + return NULL; > + > + if (p->order == BPF_ITER_CGROUP_PRE) > + return css_next_descendant_pre(curr, p->start_css); > + else if (p->order == BPF_ITER_CGROUP_POST) > + return css_next_descendant_post(curr, p->start_css); > + else > + return curr->parent; > +} > + [...]
| |