bpf/bpftool/tracelog.c

0001 // SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
0002 /* Copyright (c) 2015-2017 Daniel Borkmann */
0003 /* Copyright (c) 2018 Netronome Systems, Inc. */
0004
0005 #include <errno.h>
0006 #include <limits.h>
0007 #include <signal.h>
0008 #include <stdio.h>
0009 #include <string.h>
0010 #include <unistd.h>
0011 #include <linux/magic.h>
0012 #include <fcntl.h>
0013 #include <sys/vfs.h>
0014
0015 #include "main.h"
0016
0017 #ifndef TRACEFS_MAGIC
0018 # define TRACEFS_MAGIC  0x74726163
0019 #endif
0020
0021 #define _textify(x) #x
0022 #define textify(x)  _textify(x)
0023
0024 FILE *trace_pipe_fd;
0025 char *buff;
0026
0027 static int validate_tracefs_mnt(const char *mnt, unsigned long magic)
0028 {
0029     struct statfs st_fs;
0030
0031     if (statfs(mnt, &st_fs) < 0)
0032         return -ENOENT;
0033     if ((unsigned long)st_fs.f_type != magic)
0034         return -ENOENT;
0035
0036     return 0;
0037 }
0038
0039 static bool
0040 find_tracefs_mnt_single(unsigned long magic, char *mnt, const char *mntpt)
0041 {
0042     size_t src_len;
0043
0044     if (validate_tracefs_mnt(mntpt, magic))
0045         return false;
0046
0047     src_len = strlen(mntpt);
0048     if (src_len + 1 >= PATH_MAX) {
0049         p_err("tracefs mount point name too long");
0050         return false;
0051     }
0052
0053     strcpy(mnt, mntpt);
0054     return true;
0055 }
0056
0057 static bool get_tracefs_pipe(char *mnt)
0058 {
0059     static const char * const known_mnts[] = {
0060         "/sys/kernel/debug/tracing",
0061         "/sys/kernel/tracing",
0062         "/tracing",
0063         "/trace",
0064     };
0065     const char *pipe_name = "/trace_pipe";
0066     const char *fstype = "tracefs";
0067     char type[100], format[32];
0068     const char * const *ptr;
0069     bool found = false;
0070     FILE *fp;
0071
0072     for (ptr = known_mnts; ptr < known_mnts + ARRAY_SIZE(known_mnts); ptr++)
0073         if (find_tracefs_mnt_single(TRACEFS_MAGIC, mnt, *ptr))
0074             goto exit_found;
0075
0076     fp = fopen("/proc/mounts", "r");
0077     if (!fp)
0078         return false;
0079
0080     /* Allow room for NULL terminating byte and pipe file name */
0081     snprintf(format, sizeof(format), "%%*s %%%zds %%99s %%*s %%*d %%*d\\n",
0082          PATH_MAX - strlen(pipe_name) - 1);
0083     while (fscanf(fp, format, mnt, type) == 2)
0084         if (strcmp(type, fstype) == 0) {
0085             found = true;
0086             break;
0087         }
0088     fclose(fp);
0089
0090     /* The string from fscanf() might be truncated, check mnt is valid */
0091     if (found && validate_tracefs_mnt(mnt, TRACEFS_MAGIC))
0092         goto exit_found;
0093
0094     if (block_mount)
0095         return false;
0096
0097     p_info("could not find tracefs, attempting to mount it now");
0098     /* Most of the time, tracefs is automatically mounted by debugfs at
0099      * /sys/kernel/debug/tracing when we try to access it. If we could not
0100      * find it, it is likely that debugfs is not mounted. Let's give one
0101      * attempt at mounting just tracefs at /sys/kernel/tracing.
0102      */
0103     strcpy(mnt, known_mnts[1]);
0104     if (mount_tracefs(mnt))
0105         return false;
0106
0107 exit_found:
0108     strcat(mnt, pipe_name);
0109     return true;
0110 }
0111
0112 static void exit_tracelog(int signum)
0113 {
0114     fclose(trace_pipe_fd);
0115     free(buff);
0116
0117     if (json_output) {
0118         jsonw_end_array(json_wtr);
0119         jsonw_destroy(&json_wtr);
0120     }
0121
0122     exit(0);
0123 }
0124
0125 int do_tracelog(int argc, char **argv)
0126 {
0127     const struct sigaction act = {
0128         .sa_handler = exit_tracelog
0129     };
0130     char trace_pipe[PATH_MAX];
0131     size_t buff_len = 0;
0132
0133     if (json_output)
0134         jsonw_start_array(json_wtr);
0135
0136     if (!get_tracefs_pipe(trace_pipe))
0137         return -1;
0138
0139     trace_pipe_fd = fopen(trace_pipe, "r");
0140     if (!trace_pipe_fd) {
0141         p_err("could not open trace pipe: %s", strerror(errno));
0142         return -1;
0143     }
0144
0145     sigaction(SIGHUP, &act, NULL);
0146     sigaction(SIGINT, &act, NULL);
0147     sigaction(SIGTERM, &act, NULL);
0148     while (1) {
0149         ssize_t ret;
0150
0151         ret = getline(&buff, &buff_len, trace_pipe_fd);
0152         if (ret <= 0) {
0153             p_err("failed to read content from trace pipe: %s",
0154                   strerror(errno));
0155             break;
0156         }
0157         if (json_output)
0158             jsonw_string(json_wtr, buff);
0159         else
0160             printf("%s", buff);
0161     }
0162
0163     fclose(trace_pipe_fd);
0164     free(buff);
0165     return -1;
0166 }