On Thu, Jun 06, 2019 at 09:58:36AM -0700, Hechao Li wrote:
> Adding a new API libbpf_num_possible_cpus() that helps user with
> per-CPU map operations.
>
> Signed-off-by: Hechao Li <hech...@fb.com>
> ---
> tools/lib/bpf/libbpf.c | 53 ++++++++++++++++++++++++++++++++++++++++
> tools/lib/bpf/libbpf.h | 16 ++++++++++++
> tools/lib/bpf/libbpf.map | 1 +
> 3 files changed, 70 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index ba89d9727137..ea80ba6f7dfd 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -3827,3 +3827,56 @@ void bpf_program__bpil_offs_to_addr(struct
> bpf_prog_info_linear *info_linear)
> desc->array_offset, addr);
> }
> }
> +
> +int libbpf_num_possible_cpus(void)
> +{
> + static const char *fcpu = "/sys/devices/system/cpu/possible";
> + int len = 0, n = 0, il = 0, ir = 0;
> + unsigned int start = 0, end = 0;
> + static int cpus;
> + char buf[128];
> + int error = 0;
> + int fd = -1;
> +
> + if (cpus > 0)
> + return cpus;
> +
> + fd = open(fcpu, O_RDONLY);
> + if (fd < 0) {
> + error = errno;
> + pr_warning("Failed to open file %s: %s\n",
> + fcpu, strerror(error));
> + return -error;
> + }
> + len = read(fd, buf, sizeof(buf));
> + close(fd);
> + if (len <= 0) {
> + error = errno;
What is the errno when len == 0?
> + pr_warning("Failed to read # of possible cpus from %s: %s\n",
> + fcpu, strerror(error));
> + return -error;
> + }
> + if (len == sizeof(buf)) {
> + pr_warning("File %s size overflow\n", fcpu);
> + return -EOVERFLOW;
> + }
> + buf[len] = '\0';
> +
> + for (ir = 0, cpus = 0; ir <= len; ir++) {
> + /* Each sub string separated by ',' has format \d+-\d+ or \d+ */
> + if (buf[ir] == ',' || buf[ir] == '\0') {
> + buf[ir] = '\0';
> + n = sscanf(&buf[il], "%u-%u", &start, &end);
> + if (n <= 0) {
> + pr_warning("Failed to get # CPUs from %s\n",
> + &buf[il]);
> + return -EINVAL;
> + } else if (n == 1) {
> + end = start;
> + }
> + cpus += end - start + 1;
> + il = ir + 1;
> + }
> + }
> + return cpus;
> +}
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 1af0d48178c8..f5e82eb2e5d4 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -454,6 +454,22 @@ bpf_program__bpil_addr_to_offs(struct
> bpf_prog_info_linear *info_linear);
> LIBBPF_API void
> bpf_program__bpil_offs_to_addr(struct bpf_prog_info_linear *info_linear);
>
> +/*
> + * A helper function to get the number of possible CPUs before looking up
> + * per-CPU maps. Negative errno is returned on failure.
> + *
> + * Example usage:
> + *
> + * int ncpus = libbpf_num_possible_cpus();
> + * if (ncpus <= 0) {
> + * // error handling
> + * }
> + * long values[ncpus];
> + * bpf_map_lookup_elem(per_cpu_map_fd, key, values);
> + *
> + */
> +LIBBPF_API int libbpf_num_possible_cpus(void);
> +
> #ifdef __cplusplus
> } /* extern "C" */
> #endif
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 46dcda89df21..2c6d835620d2 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -172,4 +172,5 @@ LIBBPF_0.0.4 {
> btf_dump__new;
> btf__parse_elf;
> bpf_object__load_xattr;
> + libbpf_num_possible_cpus;
> } LIBBPF_0.0.3;
> --
> 2.17.1
>
