[RFC PATCH bpf-next 2/4] bpf: Introduce process open coded iterator kfuncs

[Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx>]

This patch adds kfuncs bpf_iter_process_{new,next,destroy} which allow
creation and manipulation of struct bpf_iter_process in open-coded iterator
style. BPF programs can use these kfuncs or through bpf_for_each macro to
iterate all processes in the system.

Signed-off-by: Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx>
---
 include/uapi/linux/bpf.h       |  4 ++++
 kernel/bpf/helpers.c           |  3 +++
 kernel/bpf/task_iter.c         | 31 +++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  4 ++++
 tools/lib/bpf/bpf_helpers.h    |  5 +++++
 5 files changed, 47 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 2a6e9b99564b..cfbd527e3733 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7199,4 +7199,8 @@ struct bpf_iter_css_task {
 	__u64 __opaque[1];
 } __attribute__((aligned(8)));
 
+struct bpf_iter_process {
+	__u64 __opaque[1];
+} __attribute__((aligned(8)));
+
 #endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index cf113ad24837..81a2005edc26 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2458,6 +2458,9 @@ BTF_ID_FLAGS(func, bpf_iter_num_destroy, KF_ITER_DESTROY)
 BTF_ID_FLAGS(func, bpf_iter_css_task_new, KF_ITER_NEW)
 BTF_ID_FLAGS(func, bpf_iter_css_task_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_css_task_destroy, KF_ITER_DESTROY)
+BTF_ID_FLAGS(func, bpf_iter_process_new, KF_ITER_NEW)
+BTF_ID_FLAGS(func, bpf_iter_process_next, KF_ITER_NEXT | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_iter_process_destroy, KF_ITER_DESTROY)
 BTF_ID_FLAGS(func, bpf_dynptr_adjust)
 BTF_ID_FLAGS(func, bpf_dynptr_is_null)
 BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index b1bdba40b684..a6717a76c1e0 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -862,6 +862,37 @@ __bpf_kfunc void bpf_iter_css_task_destroy(struct bpf_iter_css_task *it)
 	kfree(kit->css_it);
 }
 
+struct bpf_iter_process_kern {
+	struct task_struct *tsk;
+} __attribute__((aligned(8)));
+
+__bpf_kfunc int bpf_iter_process_new(struct bpf_iter_process *it)
+{
+	struct bpf_iter_process_kern *kit = (void *)it;
+
+	BUILD_BUG_ON(sizeof(struct bpf_iter_process_kern) != sizeof(struct bpf_iter_process));
+	BUILD_BUG_ON(__alignof__(struct bpf_iter_process_kern) !=
+					__alignof__(struct bpf_iter_process));
+
+	rcu_read_lock();
+	kit->tsk = &init_task;
+	return 0;
+}
+
+__bpf_kfunc struct task_struct *bpf_iter_process_next(struct bpf_iter_process *it)
+{
+	struct bpf_iter_process_kern *kit = (void *)it;
+
+	kit->tsk = next_task(kit->tsk);
+
+	return kit->tsk == &init_task ? NULL : kit->tsk;
+}
+
+__bpf_kfunc void bpf_iter_process_destroy(struct bpf_iter_process *it)
+{
+	rcu_read_unlock();
+}
+
 DEFINE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work);
 
 static void do_mmap_read_unlock(struct irq_work *entry)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 2a6e9b99564b..cfbd527e3733 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7199,4 +7199,8 @@ struct bpf_iter_css_task {
 	__u64 __opaque[1];
 } __attribute__((aligned(8)));
 
+struct bpf_iter_process {
+	__u64 __opaque[1];
+} __attribute__((aligned(8)));
+
 #endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index f4d74b2aaddd..7d6a828d98b5 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -309,6 +309,11 @@ extern int bpf_iter_css_task_new(struct bpf_iter_css_task *it,
 extern struct task_struct *bpf_iter_css_task_next(struct bpf_iter_css_task *it) __weak __ksym;
 extern void bpf_iter_css_task_destroy(struct bpf_iter_css_task *it) __weak __ksym;
 
+struct bpf_iter_process;
+extern int bpf_iter_process_new(struct bpf_iter_process *it) __weak __ksym;
+extern struct task_struct *bpf_iter_process_next(struct bpf_iter_process *it) __weak __ksym;
+extern void bpf_iter_process_destroy(struct bpf_iter_process *it) __weak __ksym;
+
 #ifndef bpf_for_each
 /* bpf_for_each(iter_type, cur_elem, args...) provides generic construct for
  * using BPF open-coded iterators without having to write mundane explicit
-- 
2.20.1