8ed5372874
If the ftrace backend is compiled into QEMU, any attempt to start QEMU while non-root will fail due to the inability to open /sys/kernel/debug/tracing/tracing_on. Add a fallback into the code so that it connects up the trace_marker_fd variable to /dev/null when getting EACCES on the 'trace_on' file. This allows QEMU to run, with ftrace turned into a no-op. [Fixed s/setting/getting/ and s/EACCESS/EACCES/ errors pointed out by Eric Blake <eblake@redhat.com>. --Stefan] Signed-off-by: Daniel P. Berrange <berrange@redhat.com> Message-id: 1475588159-30598-13-git-send-email-berrange@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
83 lines
2.0 KiB
C
83 lines
2.0 KiB
C
/*
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* Ftrace trace backend
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*
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* Copyright (C) 2013 Hitachi, Ltd.
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* Created by Eiichi Tsukata <eiichi.tsukata.xh@hitachi.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*
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*/
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#include "qemu/osdep.h"
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#include "trace.h"
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#include "trace/control.h"
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int trace_marker_fd;
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static int find_debugfs(char *debugfs)
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{
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char type[100];
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FILE *fp;
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fp = fopen("/proc/mounts", "r");
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if (fp == NULL) {
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return 0;
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}
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while (fscanf(fp, "%*s %" STR(PATH_MAX) "s %99s %*s %*d %*d\n",
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debugfs, type) == 2) {
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if (strcmp(type, "debugfs") == 0) {
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break;
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}
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}
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fclose(fp);
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if (strcmp(type, "debugfs") != 0) {
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return 0;
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}
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return 1;
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}
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bool ftrace_init(void)
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{
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char debugfs[PATH_MAX];
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char path[PATH_MAX];
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int debugfs_found;
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int trace_fd = -1;
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debugfs_found = find_debugfs(debugfs);
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if (debugfs_found) {
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snprintf(path, PATH_MAX, "%s/tracing/tracing_on", debugfs);
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trace_fd = open(path, O_WRONLY);
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if (trace_fd < 0) {
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if (errno == EACCES) {
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trace_marker_fd = open("/dev/null", O_WRONLY);
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if (trace_marker_fd != -1) {
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return true;
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}
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}
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perror("Could not open ftrace 'tracing_on' file");
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return false;
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} else {
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if (write(trace_fd, "1", 1) < 0) {
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perror("Could not write to 'tracing_on' file");
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close(trace_fd);
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return false;
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}
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close(trace_fd);
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}
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snprintf(path, PATH_MAX, "%s/tracing/trace_marker", debugfs);
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trace_marker_fd = open(path, O_WRONLY);
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if (trace_marker_fd < 0) {
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perror("Could not open ftrace 'trace_marker' file");
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return false;
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}
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} else {
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fprintf(stderr, "debugfs is not mounted\n");
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return false;
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}
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return true;
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}
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