Commit 95d402f0 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon
Browse files

dm: add bufio 



The dm-bufio interface allows you to do cached I/O on devices,
holding recently-read blocks in memory and performing delayed writes.

We don't use buffer cache or page cache already present in the kernel, because:
* we need to handle block sizes larger than a page
* we can't allocate memory to perform reads or we'd have deadlocks

Currently, when a cache is required, we limit its size to a fraction of
available memory.  Usage can be viewed and changed in
/sys/module/dm_bufio/parameters/ .

The first user is thin provisioning, but more dm users are planned.

Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 3cf2e4ba

drivers/md/Kconfig

+8 −0
Original line number Diff line number Diff line
@@ -208,6 +208,14 @@ config DM_DEBUG 


	  If unsure, say N.



config DM_BUFIO

       tristate

       depends on BLK_DEV_DM && EXPERIMENTAL

       ---help---

	 This interface allows you to do buffered I/O on a device and acts

	 as a cache, holding recently-read blocks in memory and performing

	 delayed writes.



config DM_CRYPT

	tristate "Crypt target support"

	depends on BLK_DEV_DM

drivers/md/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -27,6 +27,7 @@ obj-$(CONFIG_MD_MULTIPATH) += multipath.o 
obj-$(CONFIG_MD_FAULTY)		+= faulty.o

obj-$(CONFIG_BLK_DEV_MD)	+= md-mod.o

obj-$(CONFIG_BLK_DEV_DM)	+= dm-mod.o

obj-$(CONFIG_DM_BUFIO)		+= dm-bufio.o

obj-$(CONFIG_DM_CRYPT)		+= dm-crypt.o

obj-$(CONFIG_DM_DELAY)		+= dm-delay.o

obj-$(CONFIG_DM_FLAKEY)		+= dm-flakey.o

drivers/md/dm-bufio.c

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+1699 −0

File added.

Preview size limit exceeded, changes collapsed.

drivers/md/dm-bufio.h

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Original line number Diff line number Diff line 
/*

 * Copyright (C) 2009-2011 Red Hat, Inc.

 *

 * Author: Mikulas Patocka <mpatocka@redhat.com>

 *

 * This file is released under the GPL.

 */



#ifndef DM_BUFIO_H

#define DM_BUFIO_H



#include <linux/blkdev.h>

#include <linux/types.h>



/*----------------------------------------------------------------*/



struct dm_bufio_client;

struct dm_buffer;



/*

 * Create a buffered IO cache on a given device

 */

struct dm_bufio_client *

dm_bufio_client_create(struct block_device *bdev, unsigned block_size,

		       unsigned reserved_buffers, unsigned aux_size,

		       void (*alloc_callback)(struct dm_buffer *),

		       void (*write_callback)(struct dm_buffer *));



/*

 * Release a buffered IO cache.

 */

void dm_bufio_client_destroy(struct dm_bufio_client *c);



/*

 * WARNING: to avoid deadlocks, these conditions are observed:

 *

 * - At most one thread can hold at most "reserved_buffers" simultaneously.

 * - Each other threads can hold at most one buffer.

 * - Threads which call only dm_bufio_get can hold unlimited number of

 *   buffers.

 */



/*

 * Read a given block from disk. Returns pointer to data.  Returns a

 * pointer to dm_buffer that can be used to release the buffer or to make

 * it dirty.

 */

void *dm_bufio_read(struct dm_bufio_client *c, sector_t block,

		    struct dm_buffer **bp);



/*

 * Like dm_bufio_read, but return buffer from cache, don't read

 * it. If the buffer is not in the cache, return NULL.

 */

void *dm_bufio_get(struct dm_bufio_client *c, sector_t block,

		   struct dm_buffer **bp);



/*

 * Like dm_bufio_read, but don't read anything from the disk.  It is

 * expected that the caller initializes the buffer and marks it dirty.

 */

void *dm_bufio_new(struct dm_bufio_client *c, sector_t block,

		   struct dm_buffer **bp);



/*

 * Release a reference obtained with dm_bufio_{read,get,new}. The data

 * pointer and dm_buffer pointer is no longer valid after this call.

 */

void dm_bufio_release(struct dm_buffer *b);



/*

 * Mark a buffer dirty. It should be called after the buffer is modified.

 *

 * In case of memory pressure, the buffer may be written after

 * dm_bufio_mark_buffer_dirty, but before dm_bufio_write_dirty_buffers.  So

 * dm_bufio_write_dirty_buffers guarantees that the buffer is on-disk but

 * the actual writing may occur earlier.

 */

void dm_bufio_mark_buffer_dirty(struct dm_buffer *b);



/*

 * Initiate writing of dirty buffers, without waiting for completion.

 */

void dm_bufio_write_dirty_buffers_async(struct dm_bufio_client *c);



/*

 * Write all dirty buffers. Guarantees that all dirty buffers created prior

 * to this call are on disk when this call exits.

 */

int dm_bufio_write_dirty_buffers(struct dm_bufio_client *c);



/*

 * Send an empty write barrier to the device to flush hardware disk cache.

 */

int dm_bufio_issue_flush(struct dm_bufio_client *c);



/*

 * Like dm_bufio_release but also move the buffer to the new

 * block. dm_bufio_write_dirty_buffers is needed to commit the new block.

 */

void dm_bufio_release_move(struct dm_buffer *b, sector_t new_block);



unsigned dm_bufio_get_block_size(struct dm_bufio_client *c);

sector_t dm_bufio_get_device_size(struct dm_bufio_client *c);

sector_t dm_bufio_get_block_number(struct dm_buffer *b);

void *dm_bufio_get_block_data(struct dm_buffer *b);

void *dm_bufio_get_aux_data(struct dm_buffer *b);

struct dm_bufio_client *dm_bufio_get_client(struct dm_buffer *b);



/*----------------------------------------------------------------*/



#endif

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