Merge branch 'bpf-libbpf-num-cpus'

Hechao Li says:

====================
Getting number of possible CPUs is commonly used for per-CPU BPF maps
and perf_event_maps. Add a new API libbpf_num_possible_cpus() that
helps user with per-CPU related operations and remove duplicate
implementations in bpftool and selftests.

v2: Save errno before calling pr_warning in case it is changed.
v3: Make sure libbpf_num_possible_cpus never returns 0 so that user only
    has to check if ret value < 0.
v4: Fix error code when reading 0 bytes from possible CPU file.
v5: Fix selftests compliation issue.
v6: Split commit to reuse libbpf_num_possible_cpus() into two commits:
    One commit to remove bpf_util.h from test BPF C programs.
    One commit to reuse libbpf_num_possible_cpus() in bpftools
    and bpf_util.h.
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/common.c

@@ -21,6 +21,7 @@
 #include <sys/vfs.h>
 
 #include <bpf.h>
+#include <libbpf.h> /* libbpf_num_possible_cpus */
 
 #include "main.h"
 
@@ -439,57 +440,13 @@ unsigned int get_page_size(void)
 
 unsigned int get_possible_cpus(void)
 {
-	static unsigned int result;
-	char buf[128];
-	long int n;
-	char *ptr;
-	int fd;
+	int cpus = libbpf_num_possible_cpus();
 
-	if (result)
-		return result;
-
-	fd = open("/sys/devices/system/cpu/possible", O_RDONLY);
-	if (fd < 0) {
-		p_err("can't open sysfs possible cpus");
+	if (cpus < 0) {
+		p_err("Can't get # of possible cpus: %s", strerror(-cpus));
 		exit(-1);
 	}
-
-	n = read(fd, buf, sizeof(buf));
-	if (n < 2) {
-		p_err("can't read sysfs possible cpus");
-		exit(-1);
-	}
-	close(fd);
-
-	if (n == sizeof(buf)) {
-		p_err("read sysfs possible cpus overflow");
-		exit(-1);
-	}
-
-	ptr = buf;
-	n = 0;
-	while (*ptr && *ptr != '\n') {
-		unsigned int a, b;
-
-		if (sscanf(ptr, "%u-%u", &a, &b) == 2) {
-			n += b - a + 1;
-
-			ptr = strchr(ptr, '-') + 1;
-		} else if (sscanf(ptr, "%u", &a) == 1) {
-			n++;
-		} else {
-			assert(0);
-		}
-
-		while (isdigit(*ptr))
-			ptr++;
-		if (*ptr == ',')
-			ptr++;
-	}
-
-	result = n;
-
-	return result;
+	return cpus;
 }
 
 static char *

tools/lib/bpf/libbpf.c

@@ -3827,3 +3827,60 @@ 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 = len ? errno : EINVAL;
+		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;
+		}
+	}
+	if (cpus <= 0) {
+		pr_warning("Invalid #CPUs %d from %s\n", cpus, fcpu);
+		return -EINVAL;
+	}
+	return cpus;
+}

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

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;

tools/testing/selftests/bpf/bpf_endian.h

@@ -2,6 +2,7 @@
 #ifndef __BPF_ENDIAN__
 #define __BPF_ENDIAN__
 
+#include <linux/stddef.h>
 #include <linux/swab.h>
 
 /* LLVM's BPF target selects the endianness of the CPU

tools/testing/selftests/bpf/bpf_util.h

@@ -6,44 +6,17 @@
 #include <stdlib.h>
 #include <string.h>
 #include <errno.h>
+#include <libbpf.h> /* libbpf_num_possible_cpus */
 
 static inline unsigned int bpf_num_possible_cpus(void)
 {
-	static const char *fcpu = "/sys/devices/system/cpu/possible";
-	unsigned int start, end, possible_cpus = 0;
-	char buff[128];
-	FILE *fp;
-	int len, n, i, j = 0;
+	int possible_cpus = libbpf_num_possible_cpus();
 
-	fp = fopen(fcpu, "r");
-	if (!fp) {
-		printf("Failed to open %s: '%s'!\n", fcpu, strerror(errno));
+	if (possible_cpus < 0) {
+		printf("Failed to get # of possible cpus: '%s'!\n",
+		       strerror(-possible_cpus));
 		exit(1);
 	}
-
-	if (!fgets(buff, sizeof(buff), fp)) {
-		printf("Failed to read %s!\n", fcpu);
-		exit(1);
-	}
-
-	len = strlen(buff);
-	for (i = 0; i <= len; i++) {
-		if (buff[i] == ',' || buff[i] == '\0') {
-			buff[i] = '\0';
-			n = sscanf(&buff[j], "%u-%u", &start, &end);
-			if (n <= 0) {
-				printf("Failed to retrieve # possible CPUs!\n");
-				exit(1);
-			} else if (n == 1) {
-				end = start;
-			}
-			possible_cpus += end - start + 1;
-			j = i + 1;
-		}
-	}
-
-	fclose(fp);
-
 	return possible_cpus;
 }
 

tools/testing/selftests/bpf/progs/sockmap_parse_prog.c

@@ -1,6 +1,5 @@
 #include <linux/bpf.h>
 #include "bpf_helpers.h"
-#include "bpf_util.h"
 #include "bpf_endian.h"
 
 int _version SEC("version") = 1;

tools/testing/selftests/bpf/progs/sockmap_tcp_msg_prog.c

@@ -1,6 +1,6 @@
 #include <linux/bpf.h>
+
 #include "bpf_helpers.h"
-#include "bpf_util.h"
 #include "bpf_endian.h"
 
 int _version SEC("version") = 1;

tools/testing/selftests/bpf/progs/sockmap_verdict_prog.c

@@ -1,6 +1,5 @@
 #include <linux/bpf.h>
 #include "bpf_helpers.h"
-#include "bpf_util.h"
 #include "bpf_endian.h"
 
 int _version SEC("version") = 1;

tools/testing/selftests/bpf/progs/test_sysctl_prog.c

@@ -8,7 +8,6 @@
 #include <linux/bpf.h>
 
 #include "bpf_helpers.h"
-#include "bpf_util.h"
 
 /* Max supported length of a string with unsigned long in base 10 (pow2 - 1). */
 #define MAX_ULONG_STR_LEN 0xF
@@ -16,6 +15,10 @@
 /* Max supported length of sysctl value string (pow2). */
 #define MAX_VALUE_STR_LEN 0x40
 
+#ifndef ARRAY_SIZE
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+#endif
+
 static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx)
 {
 	char tcp_mem_name[] = "net/ipv4/tcp_mem";