include/iocache.h File Reference

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Detailed Description

I/O Caching Helper Subsystem.

The IO Cache abstracts caching of disk sectors away from the device driver to reduce code duplication and allow a central location for disk cache management that can be flushed simply by the kernel, without having to ask each driver to do it indivitually.

Go to the source code of this file.

Typedefs
typedef struct sIOCache	tIOCache
	IO Cache Handle.
typedef int(*	tIOCache_WriteCallback )(Uint32 ID, Uint64 Sector, void *Buffer)
	Write Callback.
Enumerations
enum	eIOCache_Modess { IOCACHE_WRITEBACK, IOCACHE_DELAYWRITE, IOCACHE_VIRTUAL }
	I/O Cache handling modes. More...
Functions
tIOCache *	IOCache_Create (tIOCache_WriteCallback Write, Uint32 ID, int SectorSize, int CacheSize)
	Creates a new IO Cache.
int	IOCache_Read (tIOCache *Cache, Uint64 Sector, void *Buffer)
	Reads from a cached sector.
int	IOCache_Add (tIOCache *Cache, Uint64 Sector, void *Buffer)
	Adds a sector to the cache.
int	IOCache_Write (tIOCache *Cache, Uint64 Sector, void *Buffer)
	Writes to a cached sector.
void	IOCache_Flush (tIOCache *Cache)
	Flush altered sectors out to the device.
void	IOCache_Destroy (tIOCache *Cache)
	Flushes the cache and then removes it.

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Typedef Documentation

typedef int(* tIOCache_WriteCallback)(Uint32 ID, Uint64 Sector, void *Buffer)

Write Callback.

Called to write a sector back to the device

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Enumeration Type Documentation

enum eIOCache_Modess

I/O Cache handling modes.

Enumerator:

IOCACHE_WRITEBACK	Writeback. Transparently writes data straight to the device when the cache is written to.
IOCACHE_DELAYWRITE	Delay Write. Only writes when instructed to (by IOCache_Flush) or when a cached sector is being reallocated.
IOCACHE_VIRTUAL	Virtual - No Writes. Changes to the cache contents are only reflected in memory, any calls to IOCache_Flush will silently return without doing anything and if a sector is reallocated, all changes will be lost

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Function Documentation

int IOCache_Add	(	tIOCache *	Cache,
		Uint64	Sector,
		void *	Buffer
	)

Adds a sector to the cache.

Parameters:

	Cache	Cache handle returned by IOCache_Create
	Sector	Sector's ID number
	Buffer	Data to cache

Returns:

1 on success, 0 if the sector is already cached, -1 on error

tIOCache* IOCache_Create	(	tIOCache_WriteCallback	Write,
		Uint32	ID,
		int	SectorSize,
		int	CacheSize
	)

Creates a new IO Cache.

Parameters:

	Write	Function to call to write a sector to the device
	ID	ID to pass to Write
	SectorSize	Size of a cached sector
	CacheSize	Maximum number of objects that can be in the cache at one time

void IOCache_Destroy

(

tIOCache *

Cache

)

Flushes the cache and then removes it.

Parameters:

Cache

Cache handle returned by IOCache_Create

Note:

After this is called Cache is no longer valid

IOCache_Destroy writes all changed sectors to the device and then deallocates the cache for other systems to use.

void IOCache_Flush

(

tIOCache *

Cache

)

Flush altered sectors out to the device.

Parameters:

Cache

Cache handle returned by IOCache_Create

This will call the cache's write callback on each altered sector to flush the write cache.

int IOCache_Read	(	tIOCache *	Cache,
		Uint64	Sector,
		void *	Buffer
	)

Reads from a cached sector.

Parameters:

	Cache	Cache handle returned by IOCache_Create
	Sector	Sector's ID number
	Buffer	Destination for the data read

Returns:

1 if the data was read, 0 if the sector is not cached, -1 on error

int IOCache_Write	(	tIOCache *	Cache,
		Uint64	Sector,
		void *	Buffer
	)

Writes to a cached sector.

Parameters:

	Cache	Cache handle returned by IOCache_Create
	Sector	Sector's ID number
	Buffer	Data to write to the cache

Returns:

1 if the data was read, 0 if the sector is not cached, -1 on error

If the sector is in the cache, it is updated. Wether the Write callback is called depends on the selected caching behaviour.