From 95d402f057f2e208e4631893f6cd4a59c7c05e41 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Mon, 31 Oct 2011 20:19:09 +0000 Subject: 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: Mikulas Patocka Signed-off-by: Alasdair G Kergon --- drivers/md/dm-bufio.h | 112 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 112 insertions(+) create mode 100644 drivers/md/dm-bufio.h (limited to 'drivers/md/dm-bufio.h') diff --git a/drivers/md/dm-bufio.h b/drivers/md/dm-bufio.h new file mode 100644 index 000000000000..5c4c3a04e381 --- /dev/null +++ b/drivers/md/dm-bufio.h @@ -0,0 +1,112 @@ +/* + * Copyright (C) 2009-2011 Red Hat, Inc. + * + * Author: Mikulas Patocka + * + * This file is released under the GPL. + */ + +#ifndef DM_BUFIO_H +#define DM_BUFIO_H + +#include +#include + +/*----------------------------------------------------------------*/ + +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 -- cgit