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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: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
113 lines
3.4 KiB
C
113 lines
3.4 KiB
C
/*
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* Copyright (C) 2009-2011 Red Hat, Inc.
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*
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* Author: Mikulas Patocka <mpatocka@redhat.com>
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*
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* This file is released under the GPL.
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*/
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#ifndef DM_BUFIO_H
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#define DM_BUFIO_H
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#include <linux/blkdev.h>
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#include <linux/types.h>
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/*----------------------------------------------------------------*/
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struct dm_bufio_client;
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struct dm_buffer;
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/*
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* Create a buffered IO cache on a given device
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*/
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struct dm_bufio_client *
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dm_bufio_client_create(struct block_device *bdev, unsigned block_size,
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unsigned reserved_buffers, unsigned aux_size,
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void (*alloc_callback)(struct dm_buffer *),
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void (*write_callback)(struct dm_buffer *));
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/*
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* Release a buffered IO cache.
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*/
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void dm_bufio_client_destroy(struct dm_bufio_client *c);
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/*
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* WARNING: to avoid deadlocks, these conditions are observed:
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*
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* - At most one thread can hold at most "reserved_buffers" simultaneously.
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* - Each other threads can hold at most one buffer.
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* - Threads which call only dm_bufio_get can hold unlimited number of
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* buffers.
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*/
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/*
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* Read a given block from disk. Returns pointer to data. Returns a
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* pointer to dm_buffer that can be used to release the buffer or to make
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* it dirty.
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*/
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void *dm_bufio_read(struct dm_bufio_client *c, sector_t block,
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struct dm_buffer **bp);
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/*
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* Like dm_bufio_read, but return buffer from cache, don't read
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* it. If the buffer is not in the cache, return NULL.
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*/
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void *dm_bufio_get(struct dm_bufio_client *c, sector_t block,
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struct dm_buffer **bp);
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/*
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* Like dm_bufio_read, but don't read anything from the disk. It is
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* expected that the caller initializes the buffer and marks it dirty.
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*/
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void *dm_bufio_new(struct dm_bufio_client *c, sector_t block,
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struct dm_buffer **bp);
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/*
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* Release a reference obtained with dm_bufio_{read,get,new}. The data
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* pointer and dm_buffer pointer is no longer valid after this call.
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*/
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void dm_bufio_release(struct dm_buffer *b);
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/*
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* Mark a buffer dirty. It should be called after the buffer is modified.
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*
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* In case of memory pressure, the buffer may be written after
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* dm_bufio_mark_buffer_dirty, but before dm_bufio_write_dirty_buffers. So
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* dm_bufio_write_dirty_buffers guarantees that the buffer is on-disk but
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* the actual writing may occur earlier.
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*/
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void dm_bufio_mark_buffer_dirty(struct dm_buffer *b);
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/*
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* Initiate writing of dirty buffers, without waiting for completion.
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*/
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void dm_bufio_write_dirty_buffers_async(struct dm_bufio_client *c);
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/*
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* Write all dirty buffers. Guarantees that all dirty buffers created prior
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* to this call are on disk when this call exits.
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*/
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int dm_bufio_write_dirty_buffers(struct dm_bufio_client *c);
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/*
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* Send an empty write barrier to the device to flush hardware disk cache.
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*/
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int dm_bufio_issue_flush(struct dm_bufio_client *c);
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/*
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* Like dm_bufio_release but also move the buffer to the new
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* block. dm_bufio_write_dirty_buffers is needed to commit the new block.
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*/
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void dm_bufio_release_move(struct dm_buffer *b, sector_t new_block);
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unsigned dm_bufio_get_block_size(struct dm_bufio_client *c);
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sector_t dm_bufio_get_device_size(struct dm_bufio_client *c);
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sector_t dm_bufio_get_block_number(struct dm_buffer *b);
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void *dm_bufio_get_block_data(struct dm_buffer *b);
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void *dm_bufio_get_aux_data(struct dm_buffer *b);
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struct dm_bufio_client *dm_bufio_get_client(struct dm_buffer *b);
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/*----------------------------------------------------------------*/
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#endif
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