I/O classes. More...

#include "libts.h"
#include "ink_resource.h"

Include dependency graph for I_IOBuffer.h:

This graph shows which files directly or indirectly include this file:

Data Structures
class	IOBufferData
	A reference counted wrapper around fast allocated or malloced memory. More...
class	IOBufferBlock
	A linkable portion of IOBufferData. More...
class	IOBufferReader
	An independent reader from an MIOBuffer. More...
class	MIOBuffer
	A multiple reader, single writer memory buffer. More...
struct	MIOBufferAccessor
	A wrapper for either a reader or a writer of an MIOBuffer. More...
class	MIOBuffer_tracker
class	Empty_MIOBuffer_tracker
class	IOBufferBlock_tracker
class	IOBufferData_tracker
Defines
#define	TRACK_BUFFER_USER 1
#define	DEFAULT_BUFFER_NUMBER 128
#define	DEFAULT_HUGE_BUFFER_NUMBER 32
#define	MAX_MIOBUFFER_READERS 5
#define	DEFAULT_BUFFER_ALIGNMENT 8192
#define	DEFAULT_BUFFER_BASE_SIZE 128
#define	BUFFER_SIZE_INDEX_128 0
#define	BUFFER_SIZE_INDEX_256 1
#define	BUFFER_SIZE_INDEX_512 2
#define	BUFFER_SIZE_INDEX_1K 3
#define	BUFFER_SIZE_INDEX_2K 4
#define	BUFFER_SIZE_INDEX_4K 5
#define	BUFFER_SIZE_INDEX_8K 6
#define	BUFFER_SIZE_INDEX_16K 7
#define	BUFFER_SIZE_INDEX_32K 8
#define	BUFFER_SIZE_INDEX_64K 9
#define	BUFFER_SIZE_INDEX_128K 10
#define	BUFFER_SIZE_INDEX_256K 11
#define	BUFFER_SIZE_INDEX_512K 12
#define	BUFFER_SIZE_INDEX_1M 13
#define	BUFFER_SIZE_INDEX_2M 14
#define	MAX_BUFFER_SIZE_INDEX 14
#define	DEFAULT_BUFFER_SIZES (MAX_BUFFER_SIZE_INDEX+1)
#define	BUFFER_SIZE_FOR_INDEX(_i) (DEFAULT_BUFFER_BASE_SIZE * (1 << (_i)))
#define	DEFAULT_SMALL_BUFFER_SIZE BUFFER_SIZE_INDEX_512
#define	DEFAULT_LARGE_BUFFER_SIZE BUFFER_SIZE_INDEX_4K
#define	DEFAULT_TS_BUFFER_SIZE BUFFER_SIZE_INDEX_8K
#define	DEFAULT_MAX_BUFFER_SIZE BUFFER_SIZE_FOR_INDEX(MAX_BUFFER_SIZE_INDEX)
#define	MIN_IOBUFFER_SIZE BUFFER_SIZE_INDEX_128
#define	MAX_IOBUFFER_SIZE (DEFAULT_BUFFER_SIZES-1)
#define	BUFFER_SIZE_ALLOCATED(_i)
#define	BUFFER_SIZE_NOT_ALLOCATED DEFAULT_BUFFER_SIZES
#define	BUFFER_SIZE_INDEX_IS_XMALLOCED(_size_index) (_size_index < 0)
#define	BUFFER_SIZE_INDEX_IS_FAST_ALLOCATED(_size_index) (((uint64_t)_size_index) < DEFAULT_BUFFER_SIZES)
#define	BUFFER_SIZE_INDEX_IS_CONSTANT(_size_index) (_size_index >= DEFAULT_BUFFER_SIZES)
#define	BUFFER_SIZE_FOR_XMALLOC(_size) (-(_size))
#define	BUFFER_SIZE_INDEX_FOR_XMALLOC_SIZE(_size) (-(_size))
#define	BUFFER_SIZE_FOR_CONSTANT(_size) (_size - DEFAULT_BUFFER_SIZES)
#define	BUFFER_SIZE_INDEX_FOR_CONSTANT_SIZE(_size) (_size+DEFAULT_BUFFER_SIZES)
#define	new_MIOBuffer MIOBuffer_tracker(RES_PATH("memory/IOBuffer/"))
	MIOBuffer allocator/deallocator.
#define	new_empty_MIOBuffer Empty_MIOBuffer_tracker(RES_PATH("memory/IOBuffer/"))
#define	new_IOBufferBlock IOBufferBlock_tracker(RES_PATH("memory/IOBuffer/"))
	IOBufferBlock allocator.
#define	new_IOBufferData IOBufferData_tracker(RES_PATH("memory/IOBuffer/"))
#define	new_xmalloc_IOBufferData(b, size)
#define	new_constant_IOBufferData(b, size)
Enumerations
enum	AllocType { NO_ALLOC, FAST_ALLOCATED, XMALLOCED, MEMALIGNED, DEFAULT_ALLOC, CONSTANT }
Functions
void	init_buffer_allocators ()
MIOBuffer *	new_MIOBuffer_internal (const char *loc, int64_t size_index=default_large_iobuffer_size)
MIOBuffer *	new_empty_MIOBuffer_internal (const char *loc, int64_t size_index=default_large_iobuffer_size)
void	free_MIOBuffer (MIOBuffer *mio)
IOBufferBlock *	new_IOBufferBlock_internal (const char *loc)
IOBufferBlock *	new_IOBufferBlock_internal (const char loc, IOBufferData d, int64_t len=0, int64_t offset=0)
IOBufferData *	new_IOBufferData_internal (const char *location, int64_t size_index=default_large_iobuffer_size, AllocType type=DEFAULT_ALLOC)
IOBufferData *	new_xmalloc_IOBufferData_internal (const char location, void b, int64_t size)
IOBufferData *	new_constant_IOBufferData_internal (const char locaction, void b, int64_t size)
int64_t	iobuffer_size_to_index (int64_t size, int64_t max=max_iobuffer_size)
int64_t	index_to_buffer_size (int64_t idx)
IOBufferBlock *	iobufferblock_clone (IOBufferBlock *b, int64_t offset, int64_t len)
	Clone a IOBufferBlock chain.
IOBufferBlock *	iobufferblock_skip (IOBufferBlock b, int64_t poffset, int64_t *plen, int64_t write)
	Skip over specified bytes in chain.
Variables
inkcoreapi int64_t	max_iobuffer_size
int64_t	default_small_iobuffer_size
int64_t	default_large_iobuffer_size
inkcoreapi Allocator	ioBufAllocator [DEFAULT_BUFFER_SIZES]
inkcoreapi ClassAllocator < IOBufferData >	ioDataAllocator
inkcoreapi ClassAllocator < IOBufferBlock >	ioBlockAllocator

Detailed Description

I/O classes.

License

Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Watermark

Watermarks can be used as an interface between the data transferring layer (VConnection) and the user layer (a state machine). Watermarks should be used when you need to have at least a certain amount of data to make some determination. For example, when parsing a string, one might wish to ensure that an entire line will come in before consuming the data. In such a case, the water_mark should be set to the largest possible size of the string. (appropriate error handling should take care of exessively long strings).

In all other cases, especially when all data will be consumed, the water_mark should be set to 0 (the default).

Definition in file I_IOBuffer.h.

Define Documentation

#define BUFFER_SIZE_ALLOCATED ( _i )

Value:

(BUFFER_SIZE_INDEX_IS_FAST_ALLOCATED(_i) || \
   BUFFER_SIZE_INDEX_IS_XMALLOCED(_i) )

Definition at line 115 of file I_IOBuffer.h.

Referenced by IOBufferBlock::alloc(), and MIOBuffer::append_block().

#define BUFFER_SIZE_FOR_CONSTANT ( _size ) (_size - DEFAULT_BUFFER_SIZES)

Definition at line 129 of file I_IOBuffer.h.

Referenced by index_to_buffer_size().

#define BUFFER_SIZE_FOR_INDEX ( _i ) (DEFAULT_BUFFER_BASE_SIZE * (1 << (_i)))

Definition at line 106 of file I_IOBuffer.h.

Referenced by buffer_size_to_index(), ClusterHandler::dump_internal_data(), index_to_buffer_size(), iobuffer_size_to_index(), and IOBufferBlock::realloc().

#define BUFFER_SIZE_FOR_XMALLOC ( _size ) (-(_size))

Definition at line 126 of file I_IOBuffer.h.

Referenced by IOBufferData::alloc(), ClusterState::ClusterState(), index_to_buffer_size(), ClusterControl::real_alloc_data(), Cache::scan(), and OutgoingControl::set_data().

#define BUFFER_SIZE_INDEX_128 0

Definition at line 88 of file I_IOBuffer.h.

#define BUFFER_SIZE_INDEX_128K 10

Definition at line 98 of file I_IOBuffer.h.

#define BUFFER_SIZE_INDEX_16K 7

Definition at line 95 of file I_IOBuffer.h.

#define BUFFER_SIZE_INDEX_1K 3

Definition at line 91 of file I_IOBuffer.h.

#define BUFFER_SIZE_INDEX_1M 13

Definition at line 101 of file I_IOBuffer.h.

#define BUFFER_SIZE_INDEX_256 1

Definition at line 89 of file I_IOBuffer.h.

Referenced by ChunkedHandler::init_by_action().

#define BUFFER_SIZE_INDEX_256K 11

Definition at line 99 of file I_IOBuffer.h.

#define BUFFER_SIZE_INDEX_2K 4

Definition at line 92 of file I_IOBuffer.h.

#define BUFFER_SIZE_INDEX_2M 14

Definition at line 102 of file I_IOBuffer.h.

#define BUFFER_SIZE_INDEX_32K 8

Definition at line 96 of file I_IOBuffer.h.

Referenced by PrefetchBlaster::blastObject(), PluginVCCore::init(), FetchSM::init_comm(), INKUDPSendTo(), and HttpSM::setup_blind_tunnel().

#define BUFFER_SIZE_INDEX_4K 5

Definition at line 93 of file I_IOBuffer.h.

#define BUFFER_SIZE_INDEX_512 2

Definition at line 90 of file I_IOBuffer.h.

Referenced by Cache::link().

#define BUFFER_SIZE_INDEX_512K 12

Definition at line 100 of file I_IOBuffer.h.

#define BUFFER_SIZE_INDEX_64K 9

Definition at line 97 of file I_IOBuffer.h.

#define BUFFER_SIZE_INDEX_8K 6

Definition at line 94 of file I_IOBuffer.h.

#define BUFFER_SIZE_INDEX_FOR_CONSTANT_SIZE ( _size ) (_size+DEFAULT_BUFFER_SIZES)

Definition at line 130 of file I_IOBuffer.h.

Referenced by new_constant_IOBufferData_internal(), and MIOBuffer::set().

#define BUFFER_SIZE_INDEX_FOR_XMALLOC_SIZE ( _size ) (-(_size))

Definition at line 127 of file I_IOBuffer.h.

Referenced by MIOBuffer::append_xmalloced(), iobuffer_size_to_index(), new_xmalloc_IOBufferData_internal(), and MIOBuffer::set_xmalloced().

#define BUFFER_SIZE_INDEX_IS_CONSTANT ( _size_index ) (_size_index >= DEFAULT_BUFFER_SIZES)

Definition at line 123 of file I_IOBuffer.h.

Referenced by index_to_buffer_size(), and new_IOBufferData_internal().

#define BUFFER_SIZE_INDEX_IS_FAST_ALLOCATED ( _size_index ) (((uint64_t)_size_index) < DEFAULT_BUFFER_SIZES)

Definition at line 121 of file I_IOBuffer.h.

Referenced by IOBufferData::alloc(), IOBufferData::dealloc(), and index_to_buffer_size().

#define BUFFER_SIZE_INDEX_IS_XMALLOCED ( _size_index ) (_size_index < 0)

Definition at line 120 of file I_IOBuffer.h.

Referenced by IOBufferData::alloc(), IOBufferData::dealloc(), and index_to_buffer_size().

#define BUFFER_SIZE_NOT_ALLOCATED DEFAULT_BUFFER_SIZES

Definition at line 119 of file I_IOBuffer.h.

Referenced by IOBufferBlock::realloc(), and IOBufferBlock::set_internal().

#define DEFAULT_BUFFER_ALIGNMENT 8192

Definition at line 79 of file I_IOBuffer.h.

#define DEFAULT_BUFFER_BASE_SIZE 128

Definition at line 80 of file I_IOBuffer.h.

Referenced by init_buffer_allocators().

#define DEFAULT_BUFFER_NUMBER 128

Definition at line 75 of file I_IOBuffer.h.

Referenced by init_buffer_allocators().

#define DEFAULT_BUFFER_SIZES (MAX_BUFFER_SIZE_INDEX+1)

Definition at line 104 of file I_IOBuffer.h.

Referenced by ClusterProcessor::free_remote_data(), ink_event_system_init(), and main().

#define DEFAULT_HUGE_BUFFER_NUMBER 32

Definition at line 77 of file I_IOBuffer.h.

#define DEFAULT_LARGE_BUFFER_SIZE BUFFER_SIZE_INDEX_4K

Definition at line 108 of file I_IOBuffer.h.

#define DEFAULT_MAX_BUFFER_SIZE BUFFER_SIZE_FOR_INDEX(MAX_BUFFER_SIZE_INDEX)

Definition at line 110 of file I_IOBuffer.h.

Referenced by CacheContinuation::allocMsgBuffer(), ClusterHandler::build_initial_vector(), Cluster_deref(), Cluster_link(), Cluster_read(), Cluster_remove(), Cluster_write(), HttpSM::find_http_resp_buffer_size(), ClusterControl::real_alloc_data(), CacheContinuation::replyOpEvent(), ClusterVConnection::schedule_write(), ClusterHandler::valid_for_data_write(), and ClusterHandler::valid_for_freespace_write().

#define DEFAULT_SMALL_BUFFER_SIZE BUFFER_SIZE_INDEX_512

Definition at line 107 of file I_IOBuffer.h.

#define DEFAULT_TS_BUFFER_SIZE BUFFER_SIZE_INDEX_8K

Definition at line 109 of file I_IOBuffer.h.

#define MAX_BUFFER_SIZE_INDEX 14

Definition at line 103 of file I_IOBuffer.h.

Referenced by CacheContinuation::allocMsgBuffer(), ClusterHandler::build_initial_vector(), HttpSM::do_setup_post_tunnel(), RamCacheCLFUS::get(), CacheVC::handleRead(), CacheVC::handleReadDone(), new_DocEvacuator(), ClusterControl::real_alloc_data(), and ICPProcessor::start().

#define MAX_IOBUFFER_SIZE (DEFAULT_BUFFER_SIZES-1)

Definition at line 112 of file I_IOBuffer.h.

Referenced by ClusterHandler::dump_internal_data().

#define MAX_MIOBUFFER_READERS 5

Definition at line 78 of file I_IOBuffer.h.

#define MIN_IOBUFFER_SIZE BUFFER_SIZE_INDEX_128

Definition at line 111 of file I_IOBuffer.h.

#define new_constant_IOBufferData	(	b,
		size
	)

Value:

new_constant_IOBufferData_internal(RES_PATH("memory/IOBuffer/"), \
                                  (b), (size))

Definition at line 1342 of file I_IOBuffer.h.

Referenced by ClusterHandler::build_data_vector(), and ClusterHandler::build_initial_vector().

#define new_empty_MIOBuffer Empty_MIOBuffer_tracker(RES_PATH("memory/IOBuffer/"))

Definition at line 1254 of file I_IOBuffer.h.

Referenced by CheckConnect::CheckConnect(), ClusterState::ClusterState(), CacheTestSM::event_handler(), RangeTransform::handle_event(), NullTransform::handle_event(), TransformControl::handle_event(), PrefetchTransform::handle_event(), ShowCache::handleCacheEvent(), NetTesterSM::NetTesterSM(), HttpServerSession::new_connection(), HttpSM::setup_cache_read_transfer(), HttpSM::setup_server_transfer(), and TSIOBufferCreate().

#define new_IOBufferBlock IOBufferBlock_tracker(RES_PATH("memory/IOBuffer/"))

IOBufferBlock allocator.

Definition at line 1296 of file I_IOBuffer.h.

Referenced by agg_copy(), Http2Frame::alloc(), ClusterHandler::build_data_vector(), ClusterHandler::build_initial_vector(), ClusterState::ClusterState(), ClusterHandler::dump_internal_data(), INKUDPSendTo(), new_incoming_UDPPacket(), new_UDPPacket(), CacheVC::openReadFromWriter(), CacheVC::openReadMain(), ICPPeerReadCont::PeerReadStateMachine(), ClusterControl::real_alloc_data(), OutgoingControl::set_data(), and test_main().

#define new_IOBufferData IOBufferData_tracker(RES_PATH("memory/IOBuffer/"))

Definition at line 1338 of file I_IOBuffer.h.

Referenced by CacheContinuation::allocMsgBuffer(), cache_op_ClusterFunction(), cache_op_result_ClusterFunction(), ClusterState::ClusterState(), RamCacheCLFUS::get(), CacheVC::handleRead(), CacheVC::handleReadDone(), Cache::link(), new_DocEvacuator(), and Cache::scan().

#define new_MIOBuffer MIOBuffer_tracker(RES_PATH("memory/IOBuffer/"))

MIOBuffer allocator/deallocator.

Definition at line 1253 of file I_IOBuffer.h.

Referenced by HttpTunnel::allocate_redirect_postdata_buffers(), HttpTunnel::allocate_redirect_postdata_producer_buffer(), TestProxy::cacheSendGetEvent(), TestProxy::connectEvent(), HttpSM::do_setup_post_tunnel(), TransformControl::handle_event(), ObjectReloadCont::Init(), SocksProxy::init(), SocksEntry::init(), KeepAliveConn::init(), PrefetchBlaster::init(), PluginVCCore::init(), OneWayTunnel::init(), OneWayMultiTunnel::init(), ChunkedHandler::init_by_action(), FetchSM::init_comm(), NetTesterSM::NetTesterSM(), HttpServerSession::new_connection(), HttpClientSession::new_connection(), Http2ClientSession::new_connection(), ObjectReloadCont::ObjectReloadEvent(), ProtocolProbeTrampoline::ProtocolProbeTrampoline(), redirect_test(), HttpSM::setup_100_continue_transfer(), HttpSM::setup_blind_tunnel(), HttpSM::setup_cache_read_transfer(), HttpSM::setup_cache_transfer_to_transform(), setup_client_request(), HttpSM::setup_internal_transfer(), HttpSM::setup_push_transfer_to_cache(), HttpSM::setup_server_send_request(), HttpSM::setup_server_transfer(), HttpSM::setup_server_transfer_to_cache_only(), HttpSM::setup_server_transfer_to_transform(), HttpSM::setup_transfer_from_transform(), HttpSM::setup_transfer_from_transform_to_cache_only(), HttpSM::setup_transform_to_server_transfer(), CacheContinuation::setupVCdataRead(), NetVCTest::start_test(), TestAccept::startEvent(), HttpSM::state_send_server_request_header(), TSIOBufferSizedCreate(), and PrefetchUrlBlaster::udpUrlBlaster().

#define new_xmalloc_IOBufferData	(	b,
		size
	)

Value:

new_xmalloc_IOBufferData_internal(RES_PATH("memory/IOBuffer/"), \
                                  (b), (size))

Definition at line 1339 of file I_IOBuffer.h.

Referenced by CacheContinuation::allocMsgBuffer(), RamCacheCLFUS::compress_entries(), RamCacheCLFUS::get(), and RamCacheCLFUS::put().

#define TRACK_BUFFER_USER 1

Definition at line 59 of file I_IOBuffer.h.

Referenced by new_constant_IOBufferData_internal(), new_IOBufferData_internal(), and new_xmalloc_IOBufferData_internal().

Enumeration Type Documentation

enum AllocType

Enumerator:

NO_ALLOC
FAST_ALLOCATED
XMALLOCED
MEMALIGNED
DEFAULT_ALLOC
CONSTANT

Definition at line 62 of file I_IOBuffer.h.

Function Documentation

void free_MIOBuffer ( MIOBuffer * mio )

Definition at line 790 of file P_IOBuffer.h.

References MIOBuffer::_writer, MIOBuffer::dealloc_all_readers(), this_thread(), and THREAD_FREE.

Referenced by KeepAliveConnTable::append(), FetchSM::cleanUp(), ChunkedHandler::clear(), OneWayTunnel::close_source_vio(), OneWayTunnel::close_target_vio(), OneWayMultiTunnel::close_target_vio(), HttpTunnel::deallocate_buffers(), HttpTunnel::deallocate_redirect_postdata_buffers(), HttpServerSession::destroy(), HttpClientSession::destroy(), Http2ClientSession::destroy(), TestProxy::done(), CacheTestSM::event_handler(), ObjectReloadCont::free(), SocksProxy::free(), SocksEntry::free(), KeepAliveConn::free(), PrefetchBlaster::free(), TransformControl::handle_event(), PrefetchTransform::handle_event(), ShowCache::handleCacheEvent(), ProtocolProbeTrampoline::ioCompletionEvent(), ProtoVCTable< VCTentry, max_entries >::remove_entry(), HttpVCTable::remove_entry(), setup_client_request(), HttpSM::state_send_server_request_header(), TSIOBufferDestroy(), HttpSM::tunnel_handler_post_ua(), CacheContinuation::VCdataRead(), CacheTestSM::~CacheTestSM(), CheckConnect::~CheckConnect(), NetTesterSM::~NetTesterSM(), NetVCTest::~NetVCTest(), NullTransform::~NullTransform(), PrefetchTransform::~PrefetchTransform(), RangeTransform::~RangeTransform(), and SSLNextProtocolAccept::~SSLNextProtocolAccept().

int64_t index_to_buffer_size ( int64_t idx )

Definition at line 61 of file P_IOBuffer.h.

References BUFFER_SIZE_FOR_CONSTANT, BUFFER_SIZE_FOR_INDEX, BUFFER_SIZE_FOR_XMALLOC, BUFFER_SIZE_INDEX_IS_CONSTANT, BUFFER_SIZE_INDEX_IS_FAST_ALLOCATED, and BUFFER_SIZE_INDEX_IS_XMALLOCED.

Referenced by IOBufferData::alloc(), MIOBuffer::block_size(), IOBufferData::block_size(), HttpSM::find_http_resp_buffer_size(), INKUDPSendTo(), HttpSM::setup_cache_read_transfer(), and HttpSM::setup_internal_transfer().

void init_buffer_allocators ( )

Definition at line 45 of file IOBuffer.cc.

References a, DEFAULT_BUFFER_BASE_SIZE, DEFAULT_BUFFER_NUMBER, default_large_iobuffer_size, ioBufAllocator, and Allocator::re_init().

Referenced by ink_event_system_init(), and main().

int64_t iobuffer_size_to_index	(	int64_t	size,
		int64_t	max = `max_iobuffer_size`
	)

Definition at line 53 of file P_IOBuffer.h.

References BUFFER_SIZE_FOR_INDEX, BUFFER_SIZE_INDEX_FOR_XMALLOC_SIZE, and buffer_size_to_index().

Referenced by cache_op_ClusterFunction(), cache_op_result_ClusterFunction(), RamCacheCLFUS::get(), CacheVC::handleRead(), CacheVC::handleReadDone(), new_DocEvacuator(), new_incoming_UDPPacket(), new_IOBufferData_internal(), new_UDPPacket(), MIOBuffer::set_size_index(), CacheContinuation::setupVCdataRead(), and ICPProcessor::start().

IOBufferBlock* iobufferblock_clone	(	IOBufferBlock *	b,
		int64_t	offset,
		int64_t	len
	)

Clone a IOBufferBlock chain.

Used to snarf a IOBufferBlock chain w/o copy.

Parameters:

	b	head of source IOBufferBlock chain.
	offset	# bytes in the beginning to skip.
	len	bytes to copy from source.

Returns:: ptr to head of new IOBufferBlock chain.

Definition at line 75 of file P_IOBuffer.h.

References IOBufferBlock::_buf_end, IOBufferBlock::_end, IOBufferBlock::_start, IOBufferBlock::clone(), IOBufferBlock::next, and start.

Referenced by CacheVC::openReadFromWriterMain().

IOBufferBlock* iobufferblock_skip	(	IOBufferBlock *	b,
		int64_t *	poffset,
		int64_t *	plen,
		int64_t	write
	)

Skip over specified bytes in chain.

Used for dropping references.

Parameters:

	b	head of source IOBufferBlock chain.
	poffset	originally offset in b, finally offset in returned IOBufferBlock.
	plen	value of write is subtracted from plen in the function.
	write	bytes to skip.