Re: [PATCH bpf-next v4 3/3] libbpf: Use mmap to parse vmlinux BTF from sysfs

On Sat, May 10, 2025 at 5:35 AM Lorenz Bauer lmb@isovalent.com wrote:

Teach libbpf to use mmap when parsing vmlinux BTF from /sys. We don't apply this to fall-back paths on the regular file system because there is no way to ensure that modifications underlying the MAP_PRIVATE mapping are not visible to the process.

Signed-off-by: Lorenz Bauer lmb@isovalent.com

tools/lib/bpf/btf.c | 85 +++++++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 69 insertions(+), 16 deletions(-)

Almost there, see below. With those changes feel free to add my ack

Acked-by: Andrii Nakryiko andrii@kernel.org

+static struct btf *btf_parse_raw_mmap(const char *path, struct btf *base_btf) +{

•   struct stat st;
  

•   void *data;
  

•   struct btf *btf;
  

•   int fd, err;
  

•   fd = open(path, O_RDONLY);
  

•   if (fd < 0)
  

•           return libbpf_err_ptr(-errno);
  

•   if (fstat(fd, &st) < 0) {
  

•           err = -errno;
  

•           close(fd);
  

•           return libbpf_err_ptr(err);
  

•   }
  

•   data = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
  

err = -errno;

•   close(fd);
  

•   if (data == MAP_FAILED)
  

•           return NULL;
  

s/return NULL;/libbpf_err_ptr(err);/

•   btf = btf_new(data, st.st_size, base_btf, true);
  

•   if (IS_ERR(btf))
  

•           munmap(data, st.st_size);
  

•   return btf;
  

+}

static struct btf *btf_parse(const char *path, struct btf *base_btf, struct btf_ext **btf_ext) { struct btf *btf; @@ -1618,7 +1669,7 @@ struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf) goto exit_free; }

•   btf = btf_new(ptr, btf_info.btf_size, base_btf);
  

•   btf = btf_new(ptr, btf_info.btf_size, base_btf, false);
  
  

exit_free: free(ptr); @@ -1659,8 +1710,7 @@ struct btf *btf__load_from_kernel_by_id(__u32 id) static void btf_invalidate_raw_data(struct btf *btf) { if (btf->raw_data) {

•           free(btf->raw_data);
  

•           btf->raw_data = NULL;
  

•           btf_free_raw_data(btf);
    }
  

drop now unnecessary {} ?

    if (btf->raw_data_swapped) {
            free(btf->raw_data_swapped);

@@ -5331,7 +5381,10 @@ struct btf *btf__load_vmlinux_btf(void) pr_warn("kernel BTF is missing at '%s', was CONFIG_DEBUG_INFO_BTF enabled?\n", sysfs_btf_path); } else {

•           btf = btf__parse(sysfs_btf_path, NULL);
  

•           btf = btf_parse_raw_mmap(sysfs_btf_path, NULL);
  

•           if (IS_ERR_OR_NULL(btf))
  

just IS_ERR() with the fixes I pointed out above

•                   btf = btf__parse(sysfs_btf_path, NULL);
  

•           if (!btf) {
                    err = -errno;
                    pr_warn("failed to read kernel BTF from '%s': %s\n",
  
  

-- 2.49.0