linux_process_info.cpp

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// Provides process information on linux systems
// Author: Max Schwarz <max.schwarz@uni-bonn.de>

#include "linux_process_info.h"

#include <unistd.h>
#include <cstdio>
#include <cstring>

#include <fmt/format.h>

namespace rosmon
{
namespace monitor
{
namespace process_info
{

static jiffies_t g_kernel_hz = -1;
static std::size_t g_page_size = -1;

jiffies_t kernel_hz()
{
        if(g_kernel_hz == (jiffies_t)-1)
        {
                g_kernel_hz = sysconf(_SC_CLK_TCK);
                if(g_kernel_hz == (jiffies_t)-1)
                {
                        fmt::print(stderr, "Warning: Could not obtain value of USER_HZ."
                                "CPU load measurements might be inaccurate.\n"
                        );
                        g_kernel_hz = 100;
                }
        }

        return g_kernel_hz;
}

std::size_t page_size()
{
        if(g_page_size == (std::size_t)-1)
        {
                g_page_size = sysconf(_SC_PAGESIZE);
                if(g_page_size == (std::size_t)-1)
                {
                        fmt::print(stderr, "Warning: Could not obtain page size.");
                        g_page_size = 4096;
                }
        }

        return g_page_size;
}

bool readStatFile(const char* filename, ProcessStat* stat)
{
        FILE* f = fopen(filename, "r");
        if(!f)
                return false;

        char buf[1024];
        int ret = fread(buf, 1, sizeof(buf)-1, f);
        fclose(f);

        if(ret <= 0)
                return false;

        buf[ret] = 0;

        unsigned long pid = 0;
        if(sscanf(buf, "%lu", &pid) != 1)
                return false;

        // from procps: skip "(filename)"
        char* start = strrchr(buf, ')');

        if(start - buf > (int)strlen(buf) - 4)
                return false;

        // Skip ")"
        start += 2;

        unsigned long pgrp = 0;
        long long unsigned int user_jiffies = 0;
        long long unsigned int kernel_jiffies = 0;
        long long unsigned int rss_pages = 0;

        // Parse interesting fields
        ret = sscanf(start,
                "%*c " // state
                "%*u " // ppid
                "%lu " // pgrp
                "%*u " // sid
                "%*u " // tty_nr
                "%*u " // tty_pgrp
                "%*u " // flags
                "%*u " // number of minor faults
                "%*u " // number of minor faults with child's
                "%*u " // number of major faults
                "%*u " // number of major faults with child's
                "%llu " // user mode jiffies
                "%llu " // kernel mode jiffies
                "%*u " // user mode jiffies with child's
                "%*u " // kernel mode jiffies with child's
                "%*u " // priority level
                "%*u " // nice level
                "%*u " // num_threads
                "%*u " // it_real_value (obsolete, always 0)
                "%*u " // time the process started after system boot
                "%*u " // virtual memory size
                "%llu " // resident memory size
                , // many more fields follow
                &pgrp,
                &user_jiffies,
                &kernel_jiffies,
                &rss_pages
        );

        if(ret != 4)
                return false;

        stat->pid = pid;
        stat->pgrp = pgrp;
        stat->utime = user_jiffies;
        stat->stime = kernel_jiffies;
        stat->mem_rss = rss_pages * page_size();

        return true;
}


}
}
}