trace-agent-rw.c

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/*
 * Read/write thread of a guest agent for virtio-trace
 *
 * Copyright (C) 2012 Hitachi, Ltd.
 * Created by Yoshihiro Yunomae <[email protected]>
 *            Masami Hiramatsu <[email protected]>
 *
 * Licensed under GPL version 2 only.
 *
 */

#define _GNU_SOURCE
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/syscall.h>
#include "trace-agent.h"

#define READ_WAIT_USEC  100000

void *rw_thread_info_new(void)
{
    struct rw_thread_info *rw_ti;

    rw_ti = zalloc(sizeof(struct rw_thread_info));
    if (rw_ti == NULL) {
        pr_err("rw_thread_info zalloc error\n");
        exit(EXIT_FAILURE);
    }

    rw_ti->cpu_num = -1;
    rw_ti->in_fd = -1;
    rw_ti->out_fd = -1;
    rw_ti->read_pipe = -1;
    rw_ti->write_pipe = -1;
    rw_ti->pipe_size = PIPE_INIT;

    return rw_ti;
}

void *rw_thread_init(int cpu, const char *in_path, const char *out_path,
                bool stdout_flag, unsigned long pipe_size,
                struct rw_thread_info *rw_ti)
{
    int data_pipe[2];

    rw_ti->cpu_num = cpu;

    /* set read(input) fd */
    rw_ti->in_fd = open(in_path, O_RDONLY);
    if (rw_ti->in_fd == -1) {
        pr_err("Could not open in_fd (CPU:%d)\n", cpu);
        goto error;
    }

    /* set write(output) fd */
    if (!stdout_flag) {
        /* virtio-serial output mode */
        rw_ti->out_fd = open(out_path, O_WRONLY);
        if (rw_ti->out_fd == -1) {
            pr_err("Could not open out_fd (CPU:%d)\n", cpu);
            goto error;
        }
    } else
        /* stdout mode */
        rw_ti->out_fd = STDOUT_FILENO;

    if (pipe2(data_pipe, O_NONBLOCK) < 0) {
        pr_err("Could not create pipe in rw-thread(%d)\n", cpu);
        goto error;
    }

    /*
     * Size of pipe is 64kB in default based on fs/pipe.c.
     * To read/write trace data speedy, pipe size is changed.
     */
    if (fcntl(*data_pipe, F_SETPIPE_SZ, pipe_size) < 0) {
        pr_err("Could not change pipe size in rw-thread(%d)\n", cpu);
        goto error;
    }

    rw_ti->read_pipe = data_pipe[1];
    rw_ti->write_pipe = data_pipe[0];
    rw_ti->pipe_size = pipe_size;

    return NULL;

error:
    exit(EXIT_FAILURE);
}

/* Bind a thread to a cpu */
static void bind_cpu(int cpu_num)
{
    cpu_set_t mask;

    CPU_ZERO(&mask);
    CPU_SET(cpu_num, &mask);

    /* bind my thread to cpu_num by assigning zero to the first argument */
    if (sched_setaffinity(0, sizeof(mask), &mask) == -1)
        pr_err("Could not set CPU#%d affinity\n", (int)cpu_num);
}

static void *rw_thread_main(void *thread_info)
{
    ssize_t rlen, wlen;
    ssize_t ret;
    struct rw_thread_info *ts = (struct rw_thread_info *)thread_info;

    bind_cpu(ts->cpu_num);

    while (1) {
        /* Wait for a read order of trace data by Host OS */
        if (!global_run_operation) {
            pthread_mutex_lock(&mutex_notify);
            pthread_cond_wait(&cond_wakeup, &mutex_notify);
            pthread_mutex_unlock(&mutex_notify);
        }

        if (global_sig_receive)
            break;

        /*
         * Each thread read trace_pipe_raw of each cpu bounding the
         * thread, so contention of multi-threads does not occur.
         */
        rlen = splice(ts->in_fd, NULL, ts->read_pipe, NULL,
                ts->pipe_size, SPLICE_F_MOVE | SPLICE_F_MORE);

        if (rlen < 0) {
            pr_err("Splice_read in rw-thread(%d)\n", ts->cpu_num);
            goto error;
        } else if (rlen == 0) {
            /*
             * If trace data do not exist or are unreadable not
             * for exceeding the page size, splice_read returns
             * NULL. Then, this waits for being filled the data in a
             * ring-buffer.
             */
            usleep(READ_WAIT_USEC);
            pr_debug("Read retry(cpu:%d)\n", ts->cpu_num);
            continue;
        }

        wlen = 0;

        do {
            ret = splice(ts->write_pipe, NULL, ts->out_fd, NULL,
                    rlen - wlen,
                    SPLICE_F_MOVE | SPLICE_F_MORE);

            if (ret < 0) {
                pr_err("Splice_write in rw-thread(%d)\n",
                                ts->cpu_num);
                goto error;
            } else if (ret == 0)
                /*
                 * When host reader is not in time for reading
                 * trace data, guest will be stopped. This is
                 * because char dev in QEMU is not supported
                 * non-blocking mode. Then, writer might be
                 * sleep in that case.
                 * This sleep will be removed by supporting
                 * non-blocking mode.
                 */
                sleep(1);
            wlen += ret;
        } while (wlen < rlen);
    }

    return NULL;

error:
    exit(EXIT_FAILURE);
}


pthread_t rw_thread_run(struct rw_thread_info *rw_ti)
{
    int ret;
    pthread_t rw_thread_per_cpu;

    ret = pthread_create(&rw_thread_per_cpu, NULL, rw_thread_main, rw_ti);
    if (ret != 0) {
        pr_err("Could not create a rw thread(%d)\n", rw_ti->cpu_num);
        exit(EXIT_FAILURE);
    }

    return rw_thread_per_cpu;
}