2 * Copyright 2021 Andrei Pangin
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
20 #include <sys/socket.h>
30 // Check if remote JVM has already opened socket for Dynamic Attach
31 static int check_socket(int pid) {
33 snprintf(path, sizeof(path), "%s/.java_pid%d", tmp_path, pid);
36 return stat(path, &stats) == 0 && S_ISSOCK(stats.st_mode) ? 0 : -1;
39 // Check if a file is owned by current user
40 static uid_t get_file_owner(const char* path) {
42 return stat(path, &stats) == 0 ? stats.st_uid : (uid_t)-1;
45 // Force remote JVM to start Attach listener.
46 // HotSpot will start Attach listener in response to SIGQUIT if it sees .attach_pid file
47 static int start_attach_mechanism(int pid, int nspid) {
49 snprintf(path, sizeof(path), "/proc/%d/cwd/.attach_pid%d", nspid, nspid);
51 int fd = creat(path, 0660);
52 if (fd == -1 || (close(fd) == 0 && get_file_owner(path) != geteuid())) {
53 // Some mounted filesystems may change the ownership of the file.
54 // JVM will not trust such file, so it's better to remove it and try a different path
57 // Failed to create attach trigger in current directory. Retry in /tmp
58 snprintf(path, sizeof(path), "%s/.attach_pid%d", tmp_path, nspid);
59 fd = creat(path, 0660);
66 // We have to still use the host namespace pid here for the kill() call
69 // Start with 20 ms sleep and increment delay each iteration. Total timeout is 6000 ms
70 struct timespec ts = {0, 20000000};
74 result = check_socket(nspid);
75 } while (result != 0 && (ts.tv_nsec += 20000000) < 500000000);
81 // Connect to UNIX domain socket created by JVM for Dynamic Attach
82 static int connect_socket(int pid) {
83 int fd = socket(PF_UNIX, SOCK_STREAM, 0);
88 struct sockaddr_un addr;
89 addr.sun_family = AF_UNIX;
91 int bytes = snprintf(addr.sun_path, sizeof(addr.sun_path), "%s/.java_pid%d", tmp_path, pid);
92 if (bytes >= sizeof(addr.sun_path)) {
93 addr.sun_path[sizeof(addr.sun_path) - 1] = 0;
96 if (connect(fd, (struct sockaddr*)&addr, sizeof(addr)) == -1) {
103 // Send command with arguments to socket
104 static int write_command(int fd, int argc, char** argv) {
106 if (write(fd, "1", 2) <= 0) {
111 for (i = 0; i < 4; i++) {
112 const char* arg = i < argc ? argv[i] : "";
113 if (write(fd, arg, strlen(arg) + 1) <= 0) {
120 // Mirror response from remote JVM to stdout
121 static int read_response(int fd, int argc, char** argv) {
123 ssize_t bytes = read(fd, buf, sizeof(buf) - 1);
125 fprintf(stderr, "Unexpected EOF reading response\n");
127 } else if (bytes < 0) {
128 perror("Error reading response");
132 // First line of response is the command result code
134 int result = atoi(buf);
136 // Special treatment of 'load' command
137 if (result == 0 && argc > 0 && strcmp(argv[0], "load") == 0) {
138 size_t total = bytes;
139 while (total < sizeof(buf) - 1 && (bytes = read(fd, buf + total, sizeof(buf) - 1 - total)) > 0) {
140 total += (size_t)bytes;
144 // The second line is the result of 'load' command; since JDK 9 it starts from "return code: "
146 result = atoi(strncmp(buf + 2, "return code: ", 13) == 0 ? buf + 15 : buf + 2);
149 // Mirror JVM response to stdout
150 printf("JVM response code = ");
152 fwrite(buf, 1, bytes, stdout);
153 bytes = read(fd, buf, sizeof(buf));
160 int jattach_hotspot(int pid, int nspid, int argc, char** argv) {
161 if (check_socket(nspid) != 0 && start_attach_mechanism(pid, nspid) != 0) {
162 perror("Could not start attach mechanism");
166 int fd = connect_socket(nspid);
168 perror("Could not connect to socket");
172 printf("Connected to remote JVM\n");
174 if (write_command(fd, argc, argv) != 0) {
175 perror("Error writing to socket");
180 int result = read_response(fd, argc, argv);