linux/tools/testing/selftests/bpf/bpf_experimental.h

#ifndef __BPF_EXPERIMENTAL__
#define __BPF_EXPERIMENTAL__

#include <vmlinux.h>
#include <bpf/bpf_tracing.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_core_read.h>

/* Description
 *	Allocates an object of the type represented by 'local_type_id' in
 *	program BTF. User may use the bpf_core_type_id_local macro to pass the
 *	type ID of a struct in program BTF.
 *
 *	The 'local_type_id' parameter must be a known constant.
 *	The 'meta' parameter is a hidden argument that is ignored.
 * Returns
 *	A pointer to an object of the type corresponding to the passed in
 *	'local_type_id', or NULL on failure.
 */
extern void *bpf_obj_new_impl(__u64 local_type_id, void *meta) __ksym;

/* Convenience macro to wrap over bpf_obj_new_impl */
#define bpf_obj_new(type) ((type *)bpf_obj_new_impl(bpf_core_type_id_local(type), NULL))

#endif
bpf: Introduce bpf_obj_new Introduce type safe memory allocator bpf_obj_new for BPF programs. The kernel side kfunc is named bpf_obj_new_impl, as passing hidden arguments to kfuncs still requires having them in prototype, unlike BPF helpers which always take 5 arguments and have them checked using bpf_func_proto in verifier, ignoring unset argument types. Introduce __ign suffix to ignore a specific kfunc argument during type checks, then use this to introduce support for passing type metadata to the bpf_obj_new_impl kfunc. The user passes BTF ID of the type it wants to allocates in program BTF, the verifier then rewrites the first argument as the size of this type, after performing some sanity checks (to ensure it exists and it is a struct type). The second argument is also fixed up and passed by the verifier. This is the btf_struct_meta for the type being allocated. It would be needed mostly for the offset array which is required for zero initializing special fields while leaving the rest of storage in unitialized state. It would also be needed in the next patch to perform proper destruction of the object's special fields. Under the hood, bpf_obj_new will call bpf_mem_alloc and bpf_mem_free, using the any context BPF memory allocator introduced recently. To this end, a global instance of the BPF memory allocator is initialized on boot to be used for this purpose. This 'bpf_global_ma' serves all allocations for bpf_obj_new. In the future, bpf_obj_new variants will allow specifying a custom allocator. Note that now that bpf_obj_new can be used to allocate objects that can be linked to BPF linked list (when future linked list helpers are available), we need to also free the elements using bpf_mem_free. However, since the draining of elements is done outside the bpf_spin_lock, we need to do migrate_disable around the call since bpf_list_head_free can be called from map free path where migration is enabled. Otherwise, when called from BPF programs migration is already disabled. A convenience macro is included in the bpf_experimental.h header to hide over the ugly details of the implementation, leading to user code looking similar to a language level extension which allocates and constructs fields of a user type. struct bar { struct bpf_list_node node; }; struct foo { struct bpf_spin_lock lock; struct bpf_list_head head __contains(bar, node); }; void prog(void) { struct foo f; f = bpf_obj_new(typeof(f)); if (!f) return; ... } A key piece of this story is still missing, i.e. the free function, which will come in the next patch. Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Link: https://lore.kernel.org/r/20221118015614.2013203-14-memxor@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> 2022-11-18 07:26:03 +05:30			`#ifndef __BPF_EXPERIMENTAL__`
			`#define __BPF_EXPERIMENTAL__`

			`#include <vmlinux.h>`
			`#include <bpf/bpf_tracing.h>`
			`#include <bpf/bpf_helpers.h>`
			`#include <bpf/bpf_core_read.h>`

			`/* Description`
			`* Allocates an object of the type represented by 'local_type_id' in`
			`* program BTF. User may use the bpf_core_type_id_local macro to pass the`
			`* type ID of a struct in program BTF.`
			`*`
			`* The 'local_type_id' parameter must be a known constant.`
			`* The 'meta' parameter is a hidden argument that is ignored.`
			`* Returns`
			`* A pointer to an object of the type corresponding to the passed in`
			`* 'local_type_id', or NULL on failure.`
			`*/`
			`extern void bpf_obj_new_impl(__u64 local_type_id, void meta) __ksym;`

			`/* Convenience macro to wrap over bpf_obj_new_impl */`
			`#define bpf_obj_new(type) ((type *)bpf_obj_new_impl(bpf_core_type_id_local(type), NULL))`

			`#endif`