bbe3ee8dc5
This patch replaces the formerly fixed 2 KiB data alignment within the packet-stream buffer by a server-defined alignment. This has two benefits. First, when using block servers that provide small block sizes like 512 bytes, we avoid fragmenting the packet-stream buffer, which occurs when aligning 512-byte requests at 2 KiB boundaries. This reduces meta data costs for the packet-stream allocator and also allows fitting more requests into the buffer. Second, block drivers with alignment constraints dictated by the hardware can now pass those constraints to the client, thereby easing the use of zero-copy DMA directly into the packet stream. The alignment is determined by the Block::Session_client at construction time and applied by the Block::Session_client::alloc_packet method. Block-session clients should always use this method, not the 'alloc_packet' method of the packet stream (tx source) directly. The latter merely applies a default alignment of 2 KiB. At the server side, the alignment is automatically checked by block/component.h (old API) and block/request_stream.h (new API). Issue #3274
126 lines
3.1 KiB
C++
126 lines
3.1 KiB
C++
/*
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* \brief Provide a rom-file as block device (aka loop devices)
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* \author Stefan Kalkowski
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* \date 2010-07-07
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*/
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/*
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* Copyright (C) 2010-2017 Genode Labs GmbH
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*
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* This file is part of the Genode OS framework, which is distributed
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* under the terms of the GNU Affero General Public License version 3.
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*/
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#include <base/attached_rom_dataspace.h>
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#include <base/component.h>
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#include <base/log.h>
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#include <block/component.h>
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#include <rom_session/connection.h>
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using namespace Genode;
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class Rom_block : public Block::Driver
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{
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private:
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Env &_env;
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Rom_connection _rom;
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size_t _blk_sz;
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Dataspace_capability _file_cap = _rom.dataspace();
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addr_t _file_addr = _env.rm().attach(_file_cap);
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size_t _file_sz = Dataspace_client(_file_cap).size();
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size_t _blk_cnt = _file_sz / _blk_sz;
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public:
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using String = Genode::String<64UL>;
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Rom_block(Env &env, String const &name, size_t blk_sz)
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: Block::Driver(env.ram()), _env(env), _rom(env, name.string()),
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_blk_sz(blk_sz) {}
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/****************************
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** Block-driver interface **
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****************************/
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Block::Session::Info info() const override
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{
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return { .block_size = _blk_sz,
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.block_count = _blk_cnt,
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.align_log2 = log2(_blk_sz),
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.writeable = false };
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}
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void read(Block::sector_t block_number,
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size_t block_count,
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char* buffer,
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Block::Packet_descriptor &packet) override
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{
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/* sanity check block number */
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if (block_number + block_count > _file_sz / _blk_sz) {
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warning("requested blocks ", block_number, "-",
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block_number + block_count, " out of range!");
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return;
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}
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size_t offset = (size_t) block_number * _blk_sz;
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size_t size = block_count * _blk_sz;
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/* copy file content to packet payload */
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memcpy((void*)buffer, (void*)(_file_addr + offset), size);
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ack_packet(packet);
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}
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};
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struct Main
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{
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Env &env;
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Heap heap { env.ram(), env.rm() };
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struct Factory : Block::Driver_factory
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{
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Env &env;
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Heap &heap;
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Factory(Env &env, Heap &heap)
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: env(env), heap(heap) {}
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Block::Driver *create() override
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{
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Attached_rom_dataspace config(env, "config");
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Rom_block::String const file =
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config.xml().attribute_value("file", Rom_block::String());
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size_t const blk_sz =
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config.xml().attribute_value("block_size", 512UL);
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log("using file=", file, " as device with block size ", blk_sz, ".");
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try {
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return new (&heap) Rom_block(env, file, blk_sz);
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}
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catch (Rom_connection::Rom_connection_failed) {
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error("cannot open file ", file); }
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throw Service_denied();
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}
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void destroy(Block::Driver *driver) override {
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Genode::destroy(&heap, driver); }
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} factory { env, heap };
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enum { WRITEABLE = false };
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Block::Root root { env.ep(), heap, env.rm(), factory, WRITEABLE };
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Main(Env &env) : env(env) {
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env.parent().announce(env.ep().manage(root)); }
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};
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void Component::construct(Genode::Env &env) { static Main server(env); }
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