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bpf,docs: Remove references to bpf_cgroup_kptr_get()

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The bpf_cgroup_kptr_get() kfunc has been removed, and
bpf_cgroup_acquire() / bpf_cgroup_release() now have the same semantics
as bpf_task_acquire() / bpf_task_release(). This patch updates the BPF
documentation to reflect this.

Signed-off-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230411041633.179404-3-void@manifault.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
David Vernet 2023-04-10 23:16:33 -05:00 committed by Alexei Starovoitov
parent 6499fe6edc
commit ec48599abe
1 changed files with 0 additions and 68 deletions
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68
Documentation/bpf/kfuncs.rst
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@ -572,74 +572,6 @@ bpf_task_release() respectively, so we won't provide examples for them.
----
You may also acquire a reference to a ``struct cgroup`` kptr that's already
stored in a map using bpf_cgroup_kptr_get():
.. kernel-doc:: kernel/bpf/helpers.c
:identifiers: bpf_cgroup_kptr_get
Here's an example of how it can be used:
.. code-block:: c
/* struct containing the struct task_struct kptr which is actually stored in the map. */
struct __cgroups_kfunc_map_value {
struct cgroup __kptr * cgroup;
};
/* The map containing struct __cgroups_kfunc_map_value entries. */
struct {
__uint(type, BPF_MAP_TYPE_HASH);
__type(key, int);
__type(value, struct __cgroups_kfunc_map_value);
__uint(max_entries, 1);
} __cgroups_kfunc_map SEC(".maps");
/* ... */
/**
* A simple example tracepoint program showing how a
* struct cgroup kptr that is stored in a map can
* be acquired using the bpf_cgroup_kptr_get() kfunc.
*/
SEC("tp_btf/cgroup_mkdir")
int BPF_PROG(cgroup_kptr_get_example, struct cgroup *cgrp, const char *path)
{
struct cgroup *kptr;
struct __cgroups_kfunc_map_value *v;
s32 id = cgrp->self.id;
/* Assume a cgroup kptr was previously stored in the map. */
v = bpf_map_lookup_elem(&__cgroups_kfunc_map, &id);
if (!v)
return -ENOENT;
/* Acquire a reference to the cgroup kptr that's already stored in the map. */
kptr = bpf_cgroup_kptr_get(&v->cgroup);
if (!kptr)
/* If no cgroup was present in the map, it's because
* we're racing with another CPU that removed it with
* bpf_kptr_xchg() between the bpf_map_lookup_elem()
* above, and our call to bpf_cgroup_kptr_get().
* bpf_cgroup_kptr_get() internally safely handles this
* race, and will return NULL if the task is no longer
* present in the map by the time we invoke the kfunc.
*/
return -EBUSY;
/* Free the reference we just took above. Note that the
* original struct cgroup kptr is still in the map. It will
* be freed either at a later time if another context deletes
* it from the map, or automatically by the BPF subsystem if
* it's still present when the map is destroyed.
*/
bpf_cgroup_release(kptr);
return 0;
}
----
Other kfuncs available for interacting with ``struct cgroup *`` objects are
bpf_cgroup_ancestor() and bpf_cgroup_from_id(), allowing callers to access
the ancestor of a cgroup and find a cgroup by its ID, respectively. Both