L4Re/departure

Annotated libfsserver/lib/mapping/copied_page_mapper.cc

645:3047b11cc814
345:e83d6020739b
7 months ago Paul Boddie file changeset files shortlog Fixed the file_data_available result to return zero if the populated span has somehow become less than the current position in the memory region.
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/*
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 * A page mapper providing copied memory pages or deferring to another page
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 * mapper to satisfy file accesses.
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 *
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 * Copyright (C) 2021, 2022 Paul Boddie <paul@boddie.org.uk>
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 *
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 * This program is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU General Public License as
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 * published by the Free Software Foundation; either version 2 of
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 * the License, or (at your option) any later version.
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 *
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 * This program is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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 * GNU General Public License for more details.
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 *
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 * You should have received a copy of the GNU General Public License
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 * along with this program; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor,
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 * Boston, MA  02110-1301, USA
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 */
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#include <l4/re/c/dataspace.h>
 
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#include <string.h>
 
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#include "copied_page_mapper.h"
 
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/* Provide mapped pages populated with the given 'mapper', with pages obtained
 
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   from the given 'pages' collection. */
 
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CopiedPageMapper::CopiedPageMapper(GenericPageMapper *mapper)
 
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: _mapper(mapper)
 
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{
 
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    _size = _mapper->get_data_size();
 
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}
 
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/* Upon deallocation, release allocated flexpages. */
 
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CopiedPageMapper::~CopiedPageMapper()
 
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{
 
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    while (!_queue.empty())
 
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    {
 
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        Flexpage *flexpage = _queue.front();
 
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        _queue.pop_front();
 
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        _memory.release(flexpage->region);
 
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        delete flexpage;
 
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    }
 
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}
 
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/* Interface for the pager. */
 
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/* Return a flexpage providing access to the indicated file 'offset'.
 
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   The returned flexpage will either provide direct access to the underlying
 
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   file content or be a completely new flexpage modified through writes to
 
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   memory. */
 
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Flexpage *CopiedPageMapper::get(offset_t offset, map_flags_t flags)
 
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{
 
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    Flexpage *f = find(offset);
 
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    /* Defer to the underlying page mapper if no flexpage was found. */
 
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    if (f == NULL)
 
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    {
 
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        f = _mapper->get(offset, flags);
 
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        /* Replicate the underlying flexpage if writing. */
 
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        if (flags & L4RE_DS_F_W)
 
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        {
 
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            Flexpage *rf = replicate_flexpage(offset, f);
 
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            _mapper->queue(f);
 
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            f = rf;
 
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        }
 
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    }
 
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    /* Upgrade the access flags. */
 
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    f->upgrade(flags);
 
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    return f;
 
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}
 
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/* Queue the given 'flexpage'. */
 
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void CopiedPageMapper::queue(Flexpage *flexpage)
 
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{
 
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    if (dynamic_cast<CopiedFlexpage *>(flexpage) == NULL)
 
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        _mapper->queue(flexpage);
 
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}
 
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/* Flush pages in the given range from 'start' with 'size'. */
 
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void CopiedPageMapper::flush_all(offset_t start, offset_t size)
 
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{
 
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    /* NOTE: This might be superfluous since copy-on-write regions should not
 
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             update content. */
 
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    _mapper->flush_all(start, size);
 
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}
 
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/* Return the maximum extent of the mapped resource. */
 
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offset_t CopiedPageMapper::get_data_size()
 
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{
 
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    return _size;
 
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}
 
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/* Set the maximum extent of the mapped resource. */
 
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void CopiedPageMapper::set_data_size(offset_t size)
 
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{
 
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    _size = size;
 
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}
 
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/* Internal flexpage retrieval methods. */
 
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/* Find an existing flexpage for 'offset'. */
 
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Flexpage *CopiedPageMapper::find(offset_t offset)
 
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{
 
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    return _map.find(offset);
 
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}
 
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/* Replicate an underlying flexpage for the file 'offset' using the given
 
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   'flexpage'. */
 
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Flexpage *CopiedPageMapper::replicate_flexpage(offset_t offset, Flexpage *flexpage)
 
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{
 
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    /* Obtain a new memory region and a new flexpage. */
 
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    Region *region = _memory.region(flexpage->size);
 
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    Flexpage *replicated = new CopiedFlexpage(region);
 
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    /* Configure the flexpage for the file region. */
 
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    replicated->reset(offset);
 
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    /* Copy the contents of the underlying flexpage. */
 
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    memcpy((void *) region->start, (const void *) flexpage->region->start, flexpage->size);
 
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    /* Register the flexpage for future accesses and for deallocation. */
 
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    _map.insert(replicated);
 
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    _queue.push_back(replicated);
 
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    return replicated;
 
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}
 
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/* Copied flexpage constructor. */
 
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CopiedFlexpage::CopiedFlexpage(Region *region)
 
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: Flexpage(region)
 
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{
 
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}
 
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