tools: bpftool: fix reading from /proc/config.gz

/proc/config has never existed as far as I can see, but /proc/config.gz
is present on Arch Linux. Add support for decompressing config.gz using
zlib which is a mandatory dependency of libelf anyway. Replace existing
stdio functions with gzFile operations since the latter transparently
handles uncompressed and gzip-compressed files.

Cc: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Peter Wu <peter@lekensteyn.nl>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
index a7afea4..078bd0d 100644 (file)
--- a/tools/bpf/bpftool/Makefile
+++ b/tools/bpf/bpftool/Makefile
@@ -52,7 +52,7 @@ ifneq ($(EXTRA_LDFLAGS),)
 LDFLAGS += $(EXTRA_LDFLAGS)
 endif
 
-LIBS = -lelf $(LIBBPF)
+LIBS = -lelf -lz $(LIBBPF)
 
 INSTALL ?= install
 RM ?= rm -f

diff --git a/tools/bpf/bpftool/feature.c b/tools/bpf/bpftool/feature.c
index d672d90..03bdc5b 100644 (file)
--- a/tools/bpf/bpftool/feature.c
+++ b/tools/bpf/bpftool/feature.c
@@ -14,6 +14,7 @@
 
 #include <bpf.h>
 #include <libbpf.h>
+#include <zlib.h>
 
 #include "main.h"
 
@@ -284,34 +285,32 @@ static void probe_jit_limit(void)
        }
 }
 
-static char *get_kernel_config_option(FILE *fd, const char *option)
+static bool read_next_kernel_config_option(gzFile file, char *buf, size_t n,
+                                          char **value)
 {
-       size_t line_n = 0, optlen = strlen(option);
-       char *res, *strval, *line = NULL;
-       ssize_t n;
+       char *sep;
 
-       rewind(fd);
-       while ((n = getline(&line, &line_n, fd)) > 0) {
-               if (strncmp(line, option, optlen))
+       while (gzgets(file, buf, n)) {
+               if (strncmp(buf, "CONFIG_", 7))
                        continue;
-               /* Check we have at least '=', value, and '\n' */
-               if (strlen(line) < optlen + 3)
-                       continue;
-               if (*(line + optlen) != '=')
+
+               sep = strchr(buf, '=');
+               if (!sep)
                        continue;
 
                /* Trim ending '\n' */
-               line[strlen(line) - 1] = '\0';
+               buf[strlen(buf) - 1] = '\0';
+
+               /* Split on '=' and ensure that a value is present. */
+               *sep = '\0';
+               if (!sep[1])
+                       continue;
 
-               /* Copy and return config option value */
-               strval = line + optlen + 1;
-               res = strdup(strval);
-               free(line);
-               return res;
+               *value = sep + 1;
+               return true;
        }
-       free(line);
 
-       return NULL;
+       return false;
 }
 
 static void probe_kernel_image_config(void)
@@ -386,59 +385,61 @@ static void probe_kernel_image_config(void)
                /* test_bpf module for BPF tests */
                "CONFIG_TEST_BPF",
        };
-       char *value, *buf = NULL;
+       char *values[ARRAY_SIZE(options)] = { };
        struct utsname utsn;
        char path[PATH_MAX];
-       size_t i, n;
-       ssize_t ret;
-       FILE *fd;
+       gzFile file = NULL;
+       char buf[4096];
+       char *value;
+       size_t i;
 
-       if (uname(&utsn))
-               goto no_config;
+       if (!uname(&utsn)) {
+               snprintf(path, sizeof(path), "/boot/config-%s", utsn.release);
 
-       snprintf(path, sizeof(path), "/boot/config-%s", utsn.release);
+               /* gzopen also accepts uncompressed files. */
+               file = gzopen(path, "r");
+       }
 
-       fd = fopen(path, "r");
-       if (!fd && errno == ENOENT) {
-               /* Some distributions put the config file at /proc/config, give
-                * it a try.
-                * Sometimes it is also at /proc/config.gz but we do not try
-                * this one for now, it would require linking against libz.
+       if (!file) {
+               /* Some distributions build with CONFIG_IKCONFIG=y and put the
+                * config file at /proc/config.gz.
                 */
-               fd = fopen("/proc/config", "r");
+               file = gzopen("/proc/config.gz", "r");
        }
-       if (!fd) {
+       if (!file) {
                p_info("skipping kernel config, can't open file: %s",
                       strerror(errno));
-               goto no_config;
+               goto end_parse;
        }
        /* Sanity checks */
-       ret = getline(&buf, &n, fd);
-       ret = getline(&buf, &n, fd);
-       if (!buf || !ret) {
+       if (!gzgets(file, buf, sizeof(buf)) ||
+           !gzgets(file, buf, sizeof(buf))) {
                p_info("skipping kernel config, can't read from file: %s",
                       strerror(errno));
-               free(buf);
-               goto no_config;
+               goto end_parse;
        }
        if (strcmp(buf, "# Automatically generated file; DO NOT EDIT.\n")) {
                p_info("skipping kernel config, can't find correct file");
-               free(buf);
-               goto no_config;
+               goto end_parse;
        }
-       free(buf);
 
-       for (i = 0; i < ARRAY_SIZE(options); i++) {
-               value = get_kernel_config_option(fd, options[i]);
-               print_kernel_option(options[i], value);
-               free(value);
+       while (read_next_kernel_config_option(file, buf, sizeof(buf), &value)) {
+               for (i = 0; i < ARRAY_SIZE(options); i++) {
+                       if (values[i] || strcmp(buf, options[i]))
+                               continue;
+
+                       values[i] = strdup(value);
+               }
        }
-       fclose(fd);
-       return;
 
-no_config:
-       for (i = 0; i < ARRAY_SIZE(options); i++)
-               print_kernel_option(options[i], NULL);
+end_parse:
+       if (file)
+               gzclose(file);
+
+       for (i = 0; i < ARRAY_SIZE(options); i++) {
+               print_kernel_option(options[i], values[i]);
+               free(values[i]);
+       }
 }
 
 static bool probe_bpf_syscall(const char *define_prefix)