168 lines
4.4 KiB
C++
168 lines
4.4 KiB
C++
/*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* Copyright 2015 Danny Robson <danny@nerdcruft.net>
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*/
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#include "./paged.hpp"
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#include "../system.hpp"
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#include "../../except.hpp"
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#include "../../maths.hpp"
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#include "../../pointer.hpp"
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#include "../../cast.hpp"
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#include <sys/mman.h>
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using util::memory::buffer::paged;
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///////////////////////////////////////////////////////////////////////////////
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paged::paged (size_t bytes, size_t _window):
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m_window (round_to (_window, pagesize ()))
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{
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// reserve the address region with no access permissions
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m_begin = reinterpret_cast<char*> (
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mmap (nullptr, bytes, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0)
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);
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if (m_begin == MAP_FAILED)
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errno_error::throw_code ();
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// remap the initial window with read/write permissions
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m_cursor = m_begin + round_to (min (m_window, bytes), pagesize ());
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if (MAP_FAILED == mmap (m_begin,
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m_cursor - m_begin,
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PROT_READ | PROT_WRITE,
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MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, 0, 0))
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errno_error::throw_code ();
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// record the nominal end address
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m_end = m_begin + round_to (bytes, pagesize ());
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}
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//-----------------------------------------------------------------------------
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paged::~paged ()
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{
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// ignore errors in production; we don't want to double throw.
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auto res = munmap (m_begin, m_end - m_begin);
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(void)res;
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CHECK_ZERO (res);
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}
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///////////////////////////////////////////////////////////////////////////////
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char*
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paged::begin (void)
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{
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return m_begin;
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}
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//-----------------------------------------------------------------------------
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char*
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paged::end (void)
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{
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return m_end;
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}
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///////////////////////////////////////////////////////////////////////////////
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void
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paged::access (char *cursor)
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{
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if (cursor < m_cursor)
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release (cursor);
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else
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commit (cursor);
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}
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//-----------------------------------------------------------------------------
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void
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paged::commit (char *cursor)
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{
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// bail if it's already mapped
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if (cursor <= m_cursor)
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return;
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if (cursor > m_end || cursor < m_begin)
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throw std::out_of_range ("invalid commit cursor");
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// bump the request up to page aligned and tack on a little to amortize
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// syscall overheads
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cursor = align (cursor, pagesize ()) + m_window;
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cursor = min (cursor, m_end);
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if (MAP_FAILED == mmap (m_cursor,
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cursor - m_cursor,
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PROT_READ | PROT_WRITE,
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MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS,
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0, 0))
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errno_error::throw_code ();
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m_cursor = cursor;
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}
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//-----------------------------------------------------------------------------
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void
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paged::release (char *desired)
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{
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if (desired > m_end || desired < m_begin)
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throw std::out_of_range ("invalid release cursor");
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align (desired, pagesize ());
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// bail if the region is alread unmapped, or if it's not sufficiently
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// behind the current cursor.
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if (desired >= m_cursor || sign_cast<size_t> (m_cursor - desired) < m_window)
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return;
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desired += m_window;
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if (MAP_FAILED == mmap (desired,
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m_end - desired,
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PROT_NONE,
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MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS,
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0, 0))
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errno_error::throw_code ();
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m_cursor = desired;
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}
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///////////////////////////////////////////////////////////////////////////////
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size_t
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paged::size (void) const
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{
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return m_cursor - m_begin;
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}
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//-----------------------------------------------------------------------------
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size_t
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paged::capacity (void) const
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{
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return m_end - m_begin;
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}
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//-----------------------------------------------------------------------------
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size_t
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paged::window (void) const
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{
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return m_window;
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}
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