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100 lines
2.9 KiB
C++
100 lines
2.9 KiB
C++
/*
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* \brief Fast-bitmap allocator for NIC-session packet streams
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* \author Sebastian Sumpf
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* \date 2012-07-30
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*
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* This allocator can be used with a nic session. It is *not* required though.
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*/
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/*
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* Copyright (C) 2012-2017 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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#ifndef _INCLUDE__NIC__PACKET_ALLOCATOR__
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#define _INCLUDE__NIC__PACKET_ALLOCATOR__
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#include <os/packet_allocator.h>
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#include <base/log.h>
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namespace Nic { struct Packet_allocator; }
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/**
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* Packet allocator used for packet streaming in nic sessions.
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*
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* We override the allocator interface to align the IP packet to a 32-bit
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* address. The ethernet frame header contains src/dst mac (12) + ethertype (2)
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* causing the IP header to be at offset 14 in the packet. This leads to
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* problems on platforms that require load/store operations to be naturally
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* aligned when reading, for example, 4 byte IP addresses. Therefore, we
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* allocate packet size plus OFFSET and offset the returned packet allocation
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* at 2 bytes, which effectively aligns the IP header to 4 bytes.
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*
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* Note, this tweak reduces the usable bytes in the allocated packets to
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* DEFAULT_PACKET_SIZE - OFFSET and assumes word-aligned allocations in the
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* Genode::Packet_allocator. As DEFAULT_PACKET_SIZE is used for the
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* transmission-buffer calculation we could not change it without breaking the
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* API. OFFSET_PACKET_SIZE reflects the actual (usable) packet-buffer size.
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*/
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struct Nic::Packet_allocator : Genode::Packet_allocator
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{
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enum {
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DEFAULT_PACKET_SIZE = 1600,
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OFFSET = 2,
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OFFSET_PACKET_SIZE = DEFAULT_PACKET_SIZE - OFFSET,
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};
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using size_t = Genode::size_t;
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/**
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* Constructor
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*
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* \param md_alloc Meta-data allocator
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*/
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Packet_allocator(Genode::Allocator *md_alloc)
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: Genode::Packet_allocator(md_alloc, DEFAULT_PACKET_SIZE) {}
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Alloc_result try_alloc(size_t size) override
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{
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if (!size || size > OFFSET_PACKET_SIZE) {
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Genode::error("unsupported NIC packet size ", size);
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return Alloc_result { Alloc_error::DENIED };
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}
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Alloc_result result = Genode::Packet_allocator::try_alloc(size + OFFSET);
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result.with_result(
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[&] (void *content) {
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/* assume word-aligned packet buffer and offset packet by 2 bytes */
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if ((Genode::addr_t)content & 0b11) {
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Genode::error("NIC packet allocation not word-aligned");
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result = { Alloc_error::DENIED };
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} else {
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result = Alloc_result {
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reinterpret_cast<void *>((Genode::uint8_t *)content + OFFSET) };
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}
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},
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[] (Alloc_error) { }
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);
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return result;
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}
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void free(void *addr, size_t size) override
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{
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if (!size || size > OFFSET_PACKET_SIZE) {
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Genode::error("unsupported NIC packet size ", size);
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return;
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}
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Genode::Packet_allocator::free((Genode::uint8_t *)addr - OFFSET, size + OFFSET);
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}
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};
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#endif /* _INCLUDE__NIC__PACKET_ALLOCATOR__ */
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