diff mbox series

[bpf-next,3/4] bpf: Add bpf_cgroup_ancestor() kfunc

Message ID 20221122055458.173143-4-void@manifault.com (mailing list archive)
State Accepted
Commit 5ca7867078296cfa9c100f9a3b2d24be1e139825
Delegated to: BPF
Headers show
Series Support storing struct cgroup * objects as kptrs | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for bpf-next, async
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Series has a cover letter
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit fail Errors and warnings before: 23 this patch: 24
netdev/cc_maintainers success CCed 12 of 12 maintainers
netdev/build_clang success Errors and warnings before: 7 this patch: 7
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn fail Errors and warnings before: 23 this patch: 24
netdev/checkpatch warning WARNING: line length of 83 exceeds 80 columns
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
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Commit Message

David Vernet Nov. 22, 2022, 5:54 a.m. UTC 
struct cgroup * objects have a variably sized struct cgroup *ancestors[]
field which stores pointers to their ancestor cgroups. If using a cgroup
as a kptr, it can be useful to access these ancestors, but doing so
requires variable offset accesses for PTR_TO_BTF_ID, which is currently
unsupported.

This is a very useful field to access for cgroup kptrs, as programs may
wish to walk their ancestor cgroups when determining e.g. their
proportional cpu.weight. So as to enable this functionality with cgroup
kptrs before var_off is supported for PTR_TO_BTF_ID, this patch adds a
bpf_cgroup_ancestor() kfunc which accesses the cgroup node on behalf of
the caller, and acquires a reference on it. Once var_off is supported
for PTR_TO_BTF_ID, and fields inside a struct can be marked as trusted
so they retain the PTR_TRUSTED modifier when walked, this can be
removed.

Signed-off-by: David Vernet <void@manifault.com>
---
 kernel/bpf/helpers.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)
diff mbox series

Patch

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 420a4251cccc..e4e9db301db5 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1938,6 +1938,25 @@  void bpf_cgroup_release(struct cgroup *cgrp)
 
 	cgroup_put(cgrp);
 }
+
+/**
+ * bpf_cgroup_ancestor - Perform a lookup on an entry in a cgroup's ancestor
+ * array. A cgroup returned by this kfunc which is not subsequently stored in a
+ * map, must be released by calling bpf_cgroup_release().
+ * @cgrp: The cgroup for which we're performing a lookup.
+ * @level: The level of ancestor to look up.
+ */
+struct cgroup *bpf_cgroup_ancestor(struct cgroup *cgrp, int level)
+{
+	struct cgroup *ancestor;
+
+	if (level > cgrp->level || level < 0)
+		return NULL;
+
+	ancestor = cgrp->ancestors[level];
+	cgroup_get(ancestor);
+	return ancestor;
+}
 #endif /* CONFIG_CGROUPS */
 
 void *bpf_cast_to_kern_ctx(void *obj)
@@ -1970,6 +1989,7 @@  BTF_ID_FLAGS(func, bpf_task_release, KF_RELEASE)
 BTF_ID_FLAGS(func, bpf_cgroup_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, bpf_cgroup_kptr_get, KF_ACQUIRE | KF_KPTR_GET | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_cgroup_release, KF_RELEASE)
+BTF_ID_FLAGS(func, bpf_cgroup_ancestor, KF_ACQUIRE | KF_TRUSTED_ARGS | KF_RET_NULL)
 #endif
 BTF_SET8_END(generic_btf_ids)