在 32 位和 64 位 Linux : 中使用 long 的 C# pInvoke

Question

我需要调用 Linux 函数 sysinfo

它的声明是int sysinfo(struct sysinfo *信息);与

直到 Linux 2.3.16，sysinfo() 用于返回以下结构中的信息:

struct sysinfo {
    long uptime;             /* Seconds since boot */
    unsigned long loads[3];  /* 1, 5, and 15 minute load averages */
    unsigned long totalram;  /* Total usable main memory size */
    unsigned long freeram;   /* Available memory size */
    unsigned long sharedram; /* Amount of shared memory */
    unsigned long bufferram; /* Memory used by buffers */
    unsigned long totalswap; /* Total swap space size */
    unsigned long freeswap;  /* swap space still available */
    unsigned short procs;    /* Number of current processes */
    char _f[22];             /* Pads structure to 64 bytes */
};

并且大小以字节为单位给出。

从 Linux 2.3.23 (i386)、2.3.48(所有架构)开始，结构为:

struct sysinfo {
    long uptime;             /* Seconds since boot */
    unsigned long loads[3];  /* 1, 5, and 15 minute load averages */
    unsigned long totalram;  /* Total usable main memory size */
    unsigned long freeram;   /* Available memory size */
    unsigned long sharedram; /* Amount of shared memory */
    unsigned long bufferram; /* Memory used by buffers */
    unsigned long totalswap; /* Total swap space size */
    unsigned long freeswap;  /* swap space still available */
    unsigned short procs;    /* Number of current processes */
    unsigned long totalhigh; /* Total high memory size */
    unsigned long freehigh;  /* Available high memory size */
    unsigned int mem_unit;   /* Memory unit size in bytes */
    char _f[20-2*sizeof(long)-sizeof(int)]; /* Padding to 64 bytes */
};

这是我目前所拥有的:

调用函数:

private const string DoesntFindLibC =@"/lib/x86_64-linux-gnu/libc.so.6";

[System.Runtime.InteropServices.DllImport(DoesntFindLibC)]
private static extern int sysinfo(ref sysinfo_t info);  

和结构映射:

[System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
struct sysinfo_t
{
    public System.UIntPtr  uptime;             /* Seconds since boot */
    [System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst=3)]
    public System.UIntPtr [] loads;  /* 1, 5, and 15 minute load averages */


    public System.UIntPtr totalram;  /* Total usable main memory size */
    public System.UIntPtr  freeram;   /* Available memory size */
    public System.UIntPtr  sharedram; /* Amount of shared memory */
    public System.UIntPtr  bufferram; /* Memory used by buffers */


    // [System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.
    public System.UIntPtr  totalswap; /* Total swap space size */

    public System.UIntPtr  freeswap;  /* swap space still available */
    public ushort procs;    /* Number of current processes */

    [System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst=22)]
    public char[] _f; /* Pads structure to 64 bytes */
}

问题是 C 代码中的“long”是特定于处理器架构的，因为在 x86 32 位 Linux 中，long 的大小是 32 位，而在 x86 64 位 Linux 中，它是 64 位，所以我必须采用 IntPtr，因为它是无符号的，所以我采用 UIntPtr。

然而，在 C#/mono 中，long 始终被定义为 Int64。

现在使用 IntPtr 有点不方便。是否有任何我可以应用的 MarshalAs 属性，或者我可以编写的自定义编码(marshal)拆收器，以便我实际上可以在结构中包含 ulong，但它本地映射到 IntPtr ？这样相同的代码就可以在 x86-32 和 x86-64 上运行。

Answer 1

不，没有任何编码魔法可以解决这个问题。

但是您可以隐藏字段并提供属性访问器:

using System.Runtime.InteropServices;

[StructLayoutAttribute(LayoutKind.Sequential)]
struct sysinfo_t
{
    System.UIntPtr  _uptime;             /* Seconds since boot */
    public ulong uptime {
        get { return (ulong) _uptime; }
        set { _uptime = new UIntPtr (value); }
    }

    [MarshalAs(UnmanagedType.ByValArray, SizeConst=3)]
    System.UIntPtr [] _loads;  /* 1, 5, and 15 minute load averages */
    public ulong[] loads {
        get { return new ulong [] { (ulong) _loads [0], (ulong) _loads [1], (ulong) _loads [1]) };
        set { _loads = new UIntPtr [] { new UIntPtr (value [0]), new UIntPtr (value [1]), new UIntPtr (value [2]) }; }
    }

    // etc
}