code generation from C in gopsutil

Generate go code from C struct use godefs. This technique is used in the gopsutil, goport of psutil.

Transcript

1. go code generation

   from C
   r_rudi / एࢁ ࢙࿠
   

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2. Who are you?
   • @r_rudi / WAKAYAMA Shirou
   • CTO of Tsukinowa inc.
   • ansible / MQTT / Sphinx
   !
   • No.6 of Go GitHub developers in Japan
   

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3. psutil
   • A cross-platform process and system utilities
   module for Python
   • Linux/Windows/OSX/FreeBSD/Solaris
   • 32bit/64bit
   • CPU, Mem, Disk, Network, Process and so on
   

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4. gopsutil
   • go port of the psutil
   • github.com/shirou/gopsutil
   • Linux/Windows/OSX/FreeBSD
   • 32bit/64bit
   • “Pure Golang"
   

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5. How to get system information
   • Linux has proc filesystem
   • read under “/proc”
   • /proc/stat
   • /proc/mem
   • /proc/10/stat
   Thanks it’s Text
   

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6. FreeBSD/OSX
   • Some of values can get from sysctl as Text
   !
   • Some is Not Text
   • kern.devstat.all retunes “C struct devinfo_dev”
   • can not use cgo to stay “Pure golang”
   • (Linux /var/run/utmp is also not text)
   % sysctl vm.stats.vm.v_page_count
   vm.stats.vm.v_page_count: 1012332
   

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7. Use syscall.Syscall
   • call syscall of low-level operating system
   primitives directory
   Notice:

   http://golang.org/pkg shows only Linux. 

   you must read src directory to read other platform
   

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8. How to use syscall
   // freebsd MIB

   mib := []int32{CTLKern, KernDevstat, KernDevstatAll}

   

   // invoke syscall

   _, _, err = syscall.Syscall6(
   syscall.SYS___SYSCTL,
   uintptr(unsafe.Pointer(&mib[0])),
   uintptr(miblen),
   uintptr(unsafe.Pointer(&buf[0])),
   uintptr(unsafe.Pointer(&length)),
   0,
   0)
   

   // parse bytes to Devstat

   var ds Devstat
   br := bytes.NewReader(buf)
   Read(br, binary.LittleEndian, &ds)
   

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9. struct Devstat from C to Go
   type Devstat struct {
   Sequence0 uint32
   Allocated int32
   Start_count uint32
   End_count uint32
   Busy_from Bintime
   Dev_links _Ctype_struct___0
   Device_number uint32
   Device_name [16]int8
   Unit_number int32
   Bytes [4]uint64
   Operations [4]uint64
   Duration [4]Bintime
   Busy_time Bintime
   Creation_time Bintime
   Block_size uint32
   Pad_cgo_0 [4]byte
   Tag_types [3]uint64
   Flags uint32
   Device_type uint32
   Priority uint32
   Pad_cgo_1 [4]byte
   Id *byte
   Sequence1 uint32
   Pad_cgo_2 [4]byte
   }
   struct devstat {
   /* Internal house-keeping fields */
   u_int sequence0; /* Update sequence# */
   int allocated; /* Allocated entry */
   u_int start_count; /* started ops */
   u_int end_count; /* completed ops */
   struct bintime busy_from; /* */
   STAILQ_ENTRY(devstat) dev_links;
   u_int32_t device_number; /*
   * Devstat device
   * number.
   */
   char device_name[DEVSTAT_NAME_LEN];
   int unit_number;
   u_int64_t bytes[DEVSTAT_N_TRANS_FLAGS];
   u_int64_t operations[DEVSTAT_N_TRANS_FLAGS];
   struct bintime duration[DEVSTAT_N_TRANS_FLAGS];
   struct bintime busy_time;
   struct bintime creation_time; /*
   * Time the device was
   * created.
   */
   u_int32_t block_size; /* Block size, bytes */
   u_int64_t tag_types[3]; /*
   * The number of
   * simple, ordered,
   * and head of queue
   * tags sent.
   write by your self? Oh no no no!
   

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10. Use “cgo -godefs"
    // +build ignore
    package disk
    !
    /*
    #include
    #include
    #include
    */
    import "C"
    !
    type Devstat C.struct_devstat
    % go tool cgo -godefs types_freebsd.go > disk_freebsd_amd64.go
    types_freebsd.go
    Once you created definition, can use on other hosts.
    

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11. godefs
    • godef refer other struct if defined
    type Devstat C.struct_devstat

    type Bintime C.struct_bintime
    struct devstat {

    struct bintime busy_time;
    };

    struct bintime {
    time_t sec;
    uint64_t frac;
    };
    +
    type Devstat struct {
    Busy_time Bintime

    }

    type Bintime struct {
    Sec int64
    Frac uint64
    }
    

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12. limitation
    • union
    • C's union types are represented as a Go
    byte array with the same length
    • output perfect may not perfect
    • some hand editing should be required…
    

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13. Ok, how about Windows?
    • No need to use C struct
    !
    !
    !
    !
    !
    • easy, huh?
    Modkernel32 = syscall.NewLazyDLL("kernel32.dll")

    procGetDiskFreeSpaceExW = Modkernel32.NewProc("GetDiskFreeSpaceExW")

    

    lpFreeBytesAvailable := int64(0)
    lpTotalNumberOfBytes := int64(0)
    lpTotalNumberOfFreeBytes := int64(0)
    

    ret, _, err := procGetDiskFreeSpaceExW.Call(

    uintptr(unsafe.Pointer(

    syscall.StringToUTF16Ptr(path))),
    uintptr(unsafe.Pointer(&lpFreeBytesAvailable)),
    uintptr(unsafe.Pointer(&lpTotalNumberOfBytes)),
    uintptr(unsafe.Pointer(&lpTotalNumberOfFreeBytes)))
    

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14. Conclusion
    • gopsutil can get system information
    • Linux/Windows/OSX/FreeBSD
    • use syscall.Syscall to do low-level
    • use “cgo -godefs” to generate Go from C
    

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