bpf: Introduce bpf_cgroup_read_xattr to read xattr of cgroup's node

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BPF programs, such as LSM and sched_ext, would benefit from tags on
cgroups. One common practice to apply such tags is to set xattrs on
cgroupfs folders.

Introduce kfunc bpf_cgroup_read_xattr, which allows reading cgroup's
xattr.

Note that, we already have bpf_get_[file|dentry]_xattr. However, these
two APIs are not ideal for reading cgroupfs xattrs, because:

  1) These two APIs only works in sleepable contexts;
  2) There is no kfunc that matches current cgroup to cgroupfs dentry.

bpf_cgroup_read_xattr is generic and can be useful for many program
types. It is also safe, because it requires trusted or rcu protected
argument (KF_RCU). Therefore, we make it available to all program types.

Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/20250623063854.1896364-3-song@kernel.org
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

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Song Liu 2025-06-22 23:38:52 -07:00 • committed by Christian Brauner

parent d1f4e90260

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34

fs/bpf_fs_kfuncs.c

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3

kernel/bpf/helpers.c

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