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libbpf: Wire through log_true_size returned from kernel for BPF_PROG_LOAD

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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: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230406234205.323208-16-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2023-04-06 16:42:01 -07:00 • committed by Daniel Borkmann
parent fac08d45e2
commit 94e55c0fda
2 changed files with 14 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

7
tools/lib/bpf/bpf.c
View file

@ -230,9 +230,9 @@ alloc_zero_tailing_info(const void *orecord, __u32 cnt,
int bpf_prog_load(enum bpf_prog_type prog_type, int bpf_prog_load(enum bpf_prog_type prog_type,
const char *prog_name, const char *license, const char *prog_name, const char *license,
const struct bpf_insn *insns, size_t insn_cnt, 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; void *finfo = NULL, *linfo = NULL;
const char *func_info, *line_info; const char *func_info, *line_info;
__u32 log_size, log_level, attach_prog_fd, attach_btf_obj_fd; __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); fd = sys_bpf_prog_load(&attr, attr_sz, attempts);
OPTS_SET(opts, log_true_size, attr.log_true_size);
if (fd >= 0) if (fd >= 0)
return fd; 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); fd = sys_bpf_prog_load(&attr, attr_sz, attempts);
OPTS_SET(opts, log_true_size, attr.log_true_size);
if (fd >= 0) if (fd >= 0)
goto done; goto done;
} }
@ -366,6 +368,7 @@ int bpf_prog_load(enum bpf_prog_type prog_type,
attr.log_level = 1; attr.log_level = 1;
fd = sys_bpf_prog_load(&attr, attr_sz, attempts); fd = sys_bpf_prog_load(&attr, attr_sz, attempts);
OPTS_SET(opts, log_true_size, attr.log_true_size);
} }
done: done:
/* free() doesn't affect errno, so we don't need to restore it */ /* free() doesn't affect errno, so we don't need to restore it */

11
tools/lib/bpf/bpf.h
View file

@ -96,13 +96,20 @@ struct bpf_prog_load_opts {
__u32 log_level; __u32 log_level;
__u32 log_size; __u32 log_size;
char *log_buf; 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, LIBBPF_API int bpf_prog_load(enum bpf_prog_type prog_type,
const char *prog_name, const char *license, const char *prog_name, const char *license,
const struct bpf_insn *insns, size_t insn_cnt, 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 */ /* Flags to direct loading requirements */
#define MAPS_RELAX_COMPAT 0x01 #define MAPS_RELAX_COMPAT 0x01