注释此函数，int get_process_comm(pid_t pid, char **ret) { _cleanup_free_ char *escaped = NULL, *comm = NULL; int r; assert(ret); assert(pid >= 0); if (pid == 0 || pid == getpid_cached()) { comm = new0(char, TASK_COMM_LEN + 1); /* Must fit in 16 byte according to prctl(2) */ if (!comm) return -ENOMEM; if (prctl(PR_GET_NAME, comm) < 0) return -errno; } else { const char *p; p = procfs_file_alloca(pid, "comm"); /* Note that process names of kernel threads can be much longer than TASK_COMM_LEN */ r = read_one_line_file(p, &comm); if (r == -ENOENT) return -ESRCH; if (r < 0) return r; } escaped = new(char, COMM_MAX_LEN); if (!escaped) return -ENOMEM; /* Escape unprintable characters, just in case, but don't grow the string beyond the underlying size */ cellescape(escaped, COMM_MAX_LEN, comm); *ret = TAKE_PTR(escaped); return 0; }

/*
 * This function retrieves the name of the process associated with a given PID.
 * The name is returned in the ret parameter.
 *
 * Parameters:
 * pid - process ID to look up
 * ret - pointer to a char pointer that will be set to the process name
 *
 * Returns:
 * 0 on success
 * negative error code on failure
 */
int get_process_comm(pid_t pid, char **ret) {
        _cleanup_free_ char *escaped = NULL, *comm = NULL;
        int r;

        assert(ret);
        assert(pid >= 0);

        if (pid == 0 || pid == getpid_cached()) {
                /* If the PID is 0 (kernel process) or matches the current process, get the current process name using prctl */
                comm = new0(char, TASK_COMM_LEN + 1); /* Must fit in 16 bytes according to prctl(2) */
                if (!comm)
                        return -ENOMEM;

                if (prctl(PR_GET_NAME, comm) < 0)
                        return -errno;
        } else {
                /* Otherwise, read the process name from the /proc filesystem */
                const char *p;

                p = procfs_file_alloca(pid, "comm");

                /* Note that process names of kernel threads can be much longer than TASK_COMM_LEN */
                r = read_one_line_file(p, &comm);
                if (r == -ENOENT)
                        return -ESRCH;
                if (r < 0)
                        return r;
        }

        /* Escape unprintable characters, just in case, but don't grow the string beyond the underlying size */
        escaped = new(char, COMM_MAX_LEN);
        if (!escaped)
                return -ENOMEM;

        cellescape(escaped, COMM_MAX_LEN, comm);

        *ret = TAKE_PTR(escaped);
        return 0;
}

这是一个获取指定PID进程名称的函数。如果PID为0或与当前进程匹配，则使用prctl获取当前进程名称。否则，从/proc文件系统中读取进程名称。函数将返回名称，并对名称进行转义以避免不可打印字符。