Commit 94e55c0f authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Daniel Borkmann
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libbpf: Wire through log_true_size returned from kernel for BPF_PROG_LOAD 



Add output-only log_true_size field to bpf_prog_load_opts to return
bpf_attr->log_true_size value back from bpf() syscall.

Note, that we have to drop const modifier from opts in bpf_prog_load().
This could potentially cause compilation error for some users. But
the usual practice is to define bpf_prog_load_ops
as a local variable next to bpf_prog_load() call and pass pointer to it,
so const vs non-const makes no difference and won't even come up in most
(if not all) cases.

There are no runtime and ABI backwards/forward compatibility issues at all.
If user provides old struct bpf_prog_load_opts, libbpf won't set new
fields. If old libbpf is provided new bpf_prog_load_opts, nothing will
happen either as old libbpf doesn't yet know about this new field.

Adding a new variant of bpf_prog_load() just for this seems like a big
and unnecessary overkill. As a corroborating evidence is the fact that
entire selftests/bpf code base required not adjustment whatsoever.

Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230406234205.323208-16-andrii@kernel.org
parent fac08d45

tools/lib/bpf/bpf.c

+5 −2
Original line number Diff line number Diff line
@@ -230,9 +230,9 @@ alloc_zero_tailing_info(const void *orecord, __u32 cnt, 
int bpf_prog_load(enum bpf_prog_type prog_type,

		  const char *prog_name, const char *license,

		  const struct bpf_insn *insns, size_t insn_cnt,

		  const struct bpf_prog_load_opts *opts)

		  struct bpf_prog_load_opts *opts)

{

	const size_t attr_sz = offsetofend(union bpf_attr, fd_array);

	const size_t attr_sz = offsetofend(union bpf_attr, log_true_size);

	void *finfo = NULL, *linfo = NULL;

	const char *func_info, *line_info;

	__u32 log_size, log_level, attach_prog_fd, attach_btf_obj_fd;
@@ -312,6 +312,7 @@ int bpf_prog_load(enum bpf_prog_type prog_type, 
	}



	fd = sys_bpf_prog_load(&attr, attr_sz, attempts);

	OPTS_SET(opts, log_true_size, attr.log_true_size);

	if (fd >= 0)

		return fd;
@@ -352,6 +353,7 @@ int bpf_prog_load(enum bpf_prog_type prog_type, 
		}



		fd = sys_bpf_prog_load(&attr, attr_sz, attempts);

		OPTS_SET(opts, log_true_size, attr.log_true_size);

		if (fd >= 0)

			goto done;

	}
@@ -366,6 +368,7 @@ int bpf_prog_load(enum bpf_prog_type prog_type, 
		attr.log_level = 1;



		fd = sys_bpf_prog_load(&attr, attr_sz, attempts);

		OPTS_SET(opts, log_true_size, attr.log_true_size);

	}

done:

	/* free() doesn't affect errno, so we don't need to restore it */

tools/lib/bpf/bpf.h

+9 −2
Original line number Diff line number Diff line
@@ -96,13 +96,20 @@ struct bpf_prog_load_opts { 
	__u32 log_level;

	__u32 log_size;

	char *log_buf;

	/* output: actual total log contents size (including termintaing zero).

	 * It could be both larger than original log_size (if log was

	 * truncated), or smaller (if log buffer wasn't filled completely).

	 * If kernel doesn't support this feature, log_size is left unchanged.

	 */

	__u32 log_true_size;

	size_t :0;

};

#define bpf_prog_load_opts__last_field log_buf

#define bpf_prog_load_opts__last_field log_true_size



LIBBPF_API int bpf_prog_load(enum bpf_prog_type prog_type,

			     const char *prog_name, const char *license,

			     const struct bpf_insn *insns, size_t insn_cnt,

			     const struct bpf_prog_load_opts *opts);

			     struct bpf_prog_load_opts *opts);



/* Flags to direct loading requirements */

#define MAPS_RELAX_COMPAT	0x01