Memory Descriptor List

Memory Descriptor List. More...

Collaboration diagram for Memory Descriptor List:

Detailed Description

Memory Descriptor List.

The Memory Descriptor List (MDL) is a structure used to describe non-contiguous physical memory, allowing it be accessed as a single contiguous block regardless of the loaded address space.

I/O Operations

The MDL structure is primarily used to describe memory regions for I/O operations. For example, if a process specifies a buffer to write to but that I/O operation is later completed while a different address space is loaded, the kernel would be unable to access the buffer directly.

Instead, the kernel can create an MDL for the buffer, which describes the physical memory pages backing that buffer, allowing the I/O operation to be completed regardless of the currently loaded address space.

Data Structures
struct	mdl_seg_t
	Memory Descriptor List Segment structure. More...
struct	mdl_t
	Memory Descriptor List structure. More...
struct	mdl_iter_t
	Memory Descriptor List Iterator structure. More...

Macros
#define	MDL_SEGS_SMALL_MAX   2
	Amount of memory segments statically allocated for small MDLs.
#define	MDL_ITER_CREATE(_mdl)
	Create a Memory Descriptor List Iterator initializer.
#define	MDL_FOR_EACH(_byte, _mdl)   for (mdl_iter_t _iter = MDL_ITER_CREATE(_mdl); mdl_iter_next(&_iter, (_byte));)
	Iterate over bytes within a Memory Descriptor List.

Functions
static void	mdl_init (mdl_t *next, mdl_t *prev)
	Initialize a Memory Descriptor List.
void	mdl_deinit (mdl_t *mdl)
	Deinitialize a Memory Descriptor List.
void	mdl_free_chain (mdl_t *mdl, void(*free)(void *))
	Free a Memory Descriptor List chain.
uint64_t	mdl_from_region (mdl_t *mdl, mdl_t *prev, space_t *space, const void *addr, size_t size)
	Initialize a Memory Descriptor List from a memory region.
uint64_t	mdl_add (mdl_t *mdl, space_t *space, const void *addr, size_t size)
	Add a memory region to the Memory Descriptor List.
uint64_t	mdl_read (mdl_t *mdl, void *buffer, size_t count, size_t offset)
	Read from a Memory Descriptor List into a buffer.
uint64_t	mdl_write (mdl_t *mdl, const void *buffer, size_t count, size_t offset)
	Write to a Memory Descriptor List from a buffer.
static bool	mdl_iter_next (mdl_iter_t *iter, uint8_t *byte)
	Get the next byte from a Memory Descriptor List Iterator.

Macro Definition Documentation

MDL_SEGS_SMALL_MAX

#define MDL_SEGS_SMALL_MAX   2

Amount of memory segments statically allocated for small MDLs.

Definition at line 37 of file mdl.h.

MDL_ITER_CREATE

#define MDL_ITER_CREATE

(

_mdl

)

Value:

    { \
        .mdl = (_mdl), \
        .segIndex = 0, \
        .segOffset = 0, \
    }

Create a Memory Descriptor List Iterator initializer.

Parameters

_mdl	Pointer to the MDL to iterate over.

Returns

MDL Iterator initializer.

Definition at line 162 of file mdl.h.

MDL_FOR_EACH

#define MDL_FOR_EACH	(		_byte,
			_mdl
	)		for (mdl_iter_t _iter = MDL_ITER_CREATE(_mdl); mdl_iter_next(&_iter, (_byte));)

Iterate over bytes within a Memory Descriptor List.

Parameters

_byte	The iterator variable.
_mdl	Pointer to the MDL.

Definition at line 203 of file mdl.h.

Function Documentation

mdl_init()

static void mdl_init ( mdl_t *  next, mdl_t *  prev  )

inlinestatic

Initialize a Memory Descriptor List.

Parameters

next	Pointer to the MDL.
prev	Pointer to the previous MDL in the chain, or NULL if none.

Definition at line 69 of file mdl.h.

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mdl_deinit()

void mdl_deinit

(

mdl_t *

mdl

)

Deinitialize a Memory Descriptor List.

Parameters

mdl	Pointer to the MDL.

Definition at line 11 of file mdl.c.

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mdl_free_chain()

void mdl_free_chain	(	mdl_t *	mdl,
		void(*)(void *)	free
	)

Free a Memory Descriptor List chain.

Will traverse the entire chain to deinitialize and free each MDL structure using the provided free function.

Parameters

mdl	Pointer to the first MDL in the chain.
free	Function to free the MDL structure itself, or NULL to only deinitialize.

Definition at line 34 of file mdl.c.

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mdl_from_region()

uint64_t mdl_from_region	(	mdl_t *	mdl,
		mdl_t *	prev,
		space_t *	space,
		const void *	addr,
		size_t	size
	)

Initialize a Memory Descriptor List from a memory region.

Parameters

mdl	Pointer to the MDL.
prev	Pointer to the previous MDL in the chain, or NULL if none.
space	The address space of the region.
addr	The virtual address of the memory region.
size	The size of the memory region in bytes.

Returns

On success, 0. On failure, ERR and errno is set:

• See mdl_add() for possible error codes.

Definition at line 48 of file mdl.c.

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mdl_add()

uint64_t mdl_add	(	mdl_t *	mdl,
		space_t *	space,
		const void *	addr,
		size_t	size
	)

Add a memory region to the Memory Descriptor List.

Parameters

mdl	Pointer to the MDL.
space	The address space of the user process.
addr	The virtual address of the memory region.
size	The size of the memory region in bytes.

Returns

On success, 0. On failure, ERR and errno is set to:

• See mdl_add() for possible error codes.

Definition at line 125 of file mdl.c.

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mdl_read()

uint64_t mdl_read	(	mdl_t *	mdl,
		void *	buffer,
		size_t	count,
		size_t	offset
	)

Read from a Memory Descriptor List into a buffer.

Parameters

mdl	The MDL to read from.
buffer	The buffer to read into.
count	Number of bytes to read.
offset	Offset within the MDL to start reading from.

Returns

The number of bytes read.

Definition at line 153 of file mdl.c.

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mdl_write()

uint64_t mdl_write	(	mdl_t *	mdl,
		const void *	buffer,
		size_t	count,
		size_t	offset
	)

Write to a Memory Descriptor List from a buffer.

Parameters

mdl	The MDL to write to.
buffer	The buffer to write from.
count	Number of bytes to write.
offset	Offset within the MDL to start writing to.

Returns

The number of bytes written.

Definition at line 192 of file mdl.c.

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mdl_iter_next()

static bool mdl_iter_next ( mdl_iter_t *  iter, uint8_t *  byte  )

inlinestatic

Get the next byte from a Memory Descriptor List Iterator.

Parameters

iter	Pointer to the MDL Iterator.
byte	Pointer to store the retrieved byte.

Returns

true if a byte was retrieved, false if the end of the MDL was reached.

Definition at line 176 of file mdl.h.