90 lines
3.5 KiB
C
90 lines
3.5 KiB
C
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//////////////////////////////////////////////////////////////////////////////
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//
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// bootdevice.h - base class for all boot devices used by Singldr
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//
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// Copyright (c) Microsoft Corporation. All rights reserved.
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//
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#ifndef __BOOTDEVICE_H__
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#define __BOOTDEVICE_H__
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#include "singldr.h"
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// This is a virtual class for a read only filesystem device.
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//
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// 0 - Constructor
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// 1 - OpenDevice() -- initialize the device and filesystem
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// 2 - GetFileProperties() -- open a file for reading, get its
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// size and position
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// 3 - ReadFileLow() -- read a file into low memory
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// is a hack, we could do without it)
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// 4 - ReadFileHigh() -- read a file into high memory
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// 5 - CloseDevice() -- close the device
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// There is some linker wizardry going on here. We're in TINY mode, which
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// means that all code must be in the same segment, but data can reside
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// elsewhere (if it uses a __far pointer). This class definition says that
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// the data objects will be __far, but the methods themselves will be __near.
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//
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// Consider the following text:
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// struct __near [1] BootDevice
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// {
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// virtual int __near [2] OpenDevice __far [3] = 0;
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// }
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//
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// The first __near, [1], says that the classes vtable pointer is in near
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// space, i.e. is in the same code segment as CS.
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// The second __near, [2], says that the OpenDevice virtual function pointer
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// is in the near space, i.e. is in the same code segment as CS.
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// The __far, [3], says that the object is not in the common code segment,
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// as it is allocated the global heap.
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//
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extern void __far * operator new(uint cbSize);
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struct __near BootDevice
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{
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public:
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// We'll expose one public field, since it is used to adjust
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// the debug port. This lets us avoid creating a property
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// that returns a pointer to an internal field.
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uint16 __far *CmdLine;
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// each constructor will be different, as each will take parameters
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// the default constructor will do nothing:
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BootDevice() __far {};
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// As discussed above, we'll have an Init() in addition to the
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// constructor.
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// just to reiterate: every method will be __near, since the code is
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// in ds=cs=ss. The __far at the end indicates that the this pointer
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// is to an object in the far heap.
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virtual int __near OpenDevice() __far = 0;
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// We don't have free(), and we don't destroy objects, but we do
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// need a way to close down a boot medium (in particular PXE).
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virtual int __near CloseDevice() __far = 0;
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// Open the file described by filename, put its parameters in file
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// directory is used to avoid multiple allocs
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virtual int __near GetFileProperties(LPCHAR filename,
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FilePtr file,
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FilePtr directory) __far = 0;
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// Get the file described by filename/file and put it in a
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// small (32KB) buffer
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virtual INT16 __near ReadFileLow(LPCHAR filename,
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FilePtr file,
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uint8 __far * buffer) __far = 0;
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// Get the file described by filename/file and put it in high memory.
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virtual UINT32 __near ReadFileHigh(LPCHAR filename,
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FilePtr file,
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uint32 buffer,
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uint32 cbBuffer
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) __far = 0;
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};
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#endif
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