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用法示例：
Capability capability;
if (UnsafeNativeMethods.Ioctl(handle, request, ref capability) == -1)
{
throw new UnixIOException();
}
能力：
[StructLayout(LayoutKind.Sequential, Size = 104)]
internal struct Capability
{
[MarshalAs(UnmanagedType.byValTStr, SizeConst = 16)]
public String Driver;
[MarshalAs(UnmanagedType.byValTStr, SizeConst = 32)]
public String Device;
[MarshalAs(UnmanagedType.byValTStr, SizeConst = 32)]
public String BusInfo;
public uint version;
public CapabilityFlags CapabilitIEs;
}
UnsafeNativeMethods：
internal static class UnsafeNativeMethods
{
[ReliabilityContract(consistency.WillNotCorruptState, Cer.MayFail)]
[Dllimport("libc", EntryPoint = "close", SetLastError = truE)]
internal static extern int Close(IntPtr handlE);
[Dllimport("libc", EntryPoint = "ioctl", SetLastError = truE)]
internal static extern int Ioctl(SafeUnixHandle handle, uint request, ref Capability capability);
[Dllimport("libc", EntryPoint = "open", SetLastError = truE)]
internal static extern SafeUnixHandle Open(String path, uint flag, int mode);
internal static String Strerror(int error)
{
try
{
var buffer = new StringBuilder(256);
var result = Strerror(error, buffer, (ulong)buffer.Capacity);
return (result != -1) ? buffer.ToString() : null;
}
catch (EntryPointNotFoundException)
{
return null;
}
}
[Dllimport("MonoposixHelper", EntryPoint = "Mono_Posix_Syscall_strerror_r", SetLastError = truE)]
private static extern int Strerror(int error, [Out] StringBuilder buffer, ulong length);
}
SafeUnixHandle：
[SecurityPermission(SecurityAction.inheritanceDemand, UnmanagedCode = truE)]
[SecurityPermission(SecurityAction.Demand, UnmanagedCode = truE)]
internal sealed class SafeUnixHandle : SafeHandle
{
[ReliabilityContract(consistency.WillNotCorruptState, Cer.MayFail)]
private SafeUnixHandle()
: base(new IntPtr(-1), truE)
{
}
public overrIDe bool IsInvalID
{
get { return this.handle == new IntPtr(-1); }
}
[ReliabilityContract(consistency.WillNotCorruptState, Cer.MayFail)]
protected overrIDe bool ReleaseHandle()
{
return UnsafeNativeMethods.Close(this.handlE) != -1;
}
}
UnixIOException：
[serializable]
public class UnixIOException : ExternalException
{
private Readonly int nativeErrorCode;
[SecurityPermission(SecurityAction.Demand, UnmanagedCode = truE)]
public UnixIOException()
: this(Marshal.GetLastWin32Error())
{
}
[SecurityPermission(SecurityAction.Demand, UnmanagedCode = truE)]
public UnixIOException(int error)
: this(error, GetErrormessage(error))
{
}
[SecurityPermission(SecurityAction.Demand, UnmanagedCode = truE)]
public UnixIOException(String messagE)
: this(Marshal.GetLastWin32Error(), messagE)
{
}
public UnixIOException(int error, String messagE)
: base(messagE)
{
this.nativeErrorCode = error;
}
public UnixIOException(String message, Exception innerException)
: base(message, innerException)
{
}
protected UnixIOException(serializationInfo info, StreamingContext context)
: base(info, context)
{
this.nativeErrorCode = info.GeTint32("NativeErrorCode");
}
public int NativeErrorCode
{
get { return this.nativeErrorCode; }
}
public overrIDe voID GetobjectData(serializationInfo info, StreamingContext context)
{
if (info == null)
{
throw new ArgumentNullException("info");
}
info.AddValue("NativeErrorCode", this.nativeErrorCodE);
base.GetobjectData(info, context);
}
private static String GetErrormessage(int error)
{
var errorDescription = UnsafeNativeMethods.Strerror(error);
return errorDescription ?? String.Format("UnkNown error (0x{0:x})", error);
}
}
我正在开发一个需要与Video4Linux抽象交互的应用程序。该应用程序使用mono框架以C＃开发。
我面临的问题是我无法P /调用ioctl系统调用。或者，更准确地说，我可以P /调用它，但是它崩溃严重。
extern声明如下：
[DllImport("libc",EntryPoint = "ioctl",SetLastError = truE)]
private extern static int KernelIoCtrl(int fd,int request,IntPtr data);
到目前为止，一切都很好。
使用的实际例程KernelIoCtrl如下：
protected virtual int Control(IoSpecification request,object data)
{
GCHandle dataHandle;
IntPtr dataPointer = IntPtr.Zero;
try {
// Pin I/O control data
if (data != null) {
dataHandle = GCHandle.Alloc(data,GCHandleType.Pinned);
dataPointer = dataHandle.AddrOfPinnedObject();
}
// Perform I/O control
int result = KernelIoCtrl(mFileDescriptor,request.requestCode,dataPointer);
int errno = Marshal.GetLastWin32Error();
// Throw exception on errors
if (errno != (int)Errnumber.NoError)
throw new System.ComponentModel.Win32Exception(errno);
return (result);
} finally {
if (dataPointer != IntPtr.Zero)
dataHandle.Free();
}
}
以上所有代码似乎都不错。该类IoSpecification用于按照标头规范计算I /
O请求代码（基本上，它遵循处_IOC声明的宏）/usr/include/linux/asm/ioctl.h。
该data参数是一个结构，声明如下：
[StructLayout(LayoutKind.Sequential,CharSet = CharSet.Ansi)]
public struct Capability
{
[MarshalAs(UnmanagedType.byValTStr,SizeConst = 16)]
public String Driver;
[MarshalAs(UnmanagedType.byValTStr,SizeConst = 32)]
public String Device;
[MarshalAs(UnmanagedType.byValTStr,SizeConst = 32)]
public String BusInfo;
public UInt32 Version;
public CapabilityFlags Capabilities;
[MarshalAs(UnmanagedType.byValArray,SizeConst=4)]
public UInt32[] Reserved;
}
应该模仿以下结构（在处声明/usr/include/linux/videodev2.h）：
struct v4l2_capability {
__u8 driver[16]; /* i.e. "bttv" */
__u8 card[32]; /* i.e. "Hauppauge WinTV" */
__u8 bus_info[32]; /* "PCI:" + pci_name(pci_dev) */
__u32 version; /* should use KERNEL_VERSION() */
__u32 capabilities; /* Device capabilities */
__u32 reserved[4];
};
在发生崩溃之前，IOCTL请求代码计算存在问题，并且KernelIoCtrl按预期方式工作（返回errno等于 EINVAL
）。当我更正了该错误（并确实具有正确的IOCTRL请求代码）后，该调用已开始导致崩溃。
总而言之，似乎在结构编组中存在问题，但是我看不到它出了什么问题。
我担心问题出在变量参数列表中，因为 ioctl 例程被声明为follow（从man中获取）：
int ioctl(int d,...);
但是我看到很多代码将上述例程声明为int ioctl(int d,void*);，并且可以确保特定的IOCTRL请求仅接受一个参数。
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