ladybird/Kernel/TTY/PTYMultiplexer.cpp
Tom f98ca35b83 Kernel: Improve ProcFS behavior in low memory conditions
When ProcFS could no longer allocate KBuffer objects to serve calls to
read, it would just return 0, indicating EOF. This then triggered
parsing errors because code assumed it read the file.

Because read isn't supposed to return ENOMEM, change ProcFS to populate
the file data upon file open or seek to the beginning. This also means
that calls to open can now return ENOMEM if needed. This allows the
caller to either be able to successfully open the file and read it, or
fail to open it in the first place.
2021-01-03 22:12:19 +01:00

86 lines
2.8 KiB
C++

/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "PTYMultiplexer.h"
#include "MasterPTY.h"
#include <AK/Singleton.h>
#include <Kernel/FileSystem/FileDescription.h>
#include <Kernel/Process.h>
#include <LibC/errno_numbers.h>
//#define PTMX_DEBUG
namespace Kernel {
static const unsigned s_max_pty_pairs = 8;
static AK::Singleton<PTYMultiplexer> s_the;
PTYMultiplexer& PTYMultiplexer::the()
{
return *s_the;
}
PTYMultiplexer::PTYMultiplexer()
: CharacterDevice(5, 2)
{
m_freelist.ensure_capacity(s_max_pty_pairs);
for (int i = s_max_pty_pairs; i > 0; --i)
m_freelist.unchecked_append(i - 1);
}
PTYMultiplexer::~PTYMultiplexer()
{
}
KResultOr<NonnullRefPtr<FileDescription>> PTYMultiplexer::open(int options)
{
LOCKER(m_lock);
if (m_freelist.is_empty())
return KResult(-EBUSY);
auto master_index = m_freelist.take_last();
auto master = adopt(*new MasterPTY(master_index));
#ifdef PTMX_DEBUG
dbg() << "PTYMultiplexer::open: Vending master " << master->index();
#endif
auto description = FileDescription::create(move(master));
if (!description.is_error()) {
description.value()->set_rw_mode(options);
description.value()->set_file_flags(options);
}
return description;
}
void PTYMultiplexer::notify_master_destroyed(Badge<MasterPTY>, unsigned index)
{
LOCKER(m_lock);
m_freelist.append(index);
#ifdef PTMX_DEBUG
dbg() << "PTYMultiplexer: " << index << " added to freelist";
#endif
}
}