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Kernel: Improve ProcFS behavior in low memory conditions

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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.
This commit is contained in:
Tom 2020-09-17 13:51:09 -06:00 • committed by Andreas Kling
parent b36f57e570
commit f98ca35b83
24 changed files with 398 additions and 243 deletions
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55
Kernel/KBufferBuilder.cpp
View file

@ -31,32 +31,65 @@
namespace Kernel {
inline bool KBufferBuilder::can_append(size_t size) const
inline bool KBufferBuilder::check_expand(size_t size)
{
if (!m_buffer)
return false;
return ((m_size + size) < m_buffer->size());
if ((m_size + size) < m_buffer->capacity())
return true;
if (!m_can_expand)
return false;
if (Checked<size_t>::addition_would_overflow(m_size, size))
return false;
size_t new_buffer_size = m_size + size;
if (Checked<size_t>::addition_would_overflow(new_buffer_size, 1 * MiB))
return false;
new_buffer_size = PAGE_ROUND_UP(new_buffer_size + 1 * MiB);
return m_buffer->expand(new_buffer_size);
}
bool KBufferBuilder::flush()
{
if (!m_buffer)
return false;
m_buffer->set_size(m_size);
return true;
}
OwnPtr<KBuffer> KBufferBuilder::build()
{
if (!m_buffer)
if (!flush())
return {};
if (!m_buffer->is_null())
m_buffer->set_size(m_size);
return m_buffer.release_nonnull();
return make<KBuffer>(move(m_buffer));
}
KBufferBuilder::KBufferBuilder()
: m_buffer(KBuffer::try_create_with_size(4 * MiB, Region::Access::Read | Region::Access::Write))
KBufferBuilder::KBufferBuilder(bool can_expand)
: m_buffer(KBufferImpl::try_create_with_size(4 * MiB, Region::Access::Read | Region::Access::Write))
, m_can_expand(can_expand)
{
}
KBufferBuilder::KBufferBuilder(RefPtr<KBufferImpl>& buffer, bool can_expand)
: m_buffer(buffer)
, m_can_expand(can_expand)
{
if (!m_buffer)
m_buffer = buffer = KBufferImpl::try_create_with_size(4 * MiB, Region::Access::Read | Region::Access::Write);
}
void KBufferBuilder::append_bytes(ReadonlyBytes bytes)
{
if (!check_expand(bytes.size()))
return;
memcpy(insertion_ptr(), bytes.data(), bytes.size());
m_size += bytes.size();
}
void KBufferBuilder::append(const StringView& str)
{
if (str.is_empty())
return;
if (!can_append(str.length()))
if (!check_expand(str.length()))
return;
memcpy(insertion_ptr(), str.characters_without_null_termination(), str.length());
m_size += str.length();
@ -66,7 +99,7 @@ void KBufferBuilder::append(const char* characters, int length)
{
if (!length)
return;
if (!can_append(length))
if (!check_expand(length))
return;
memcpy(insertion_ptr(), characters, length);
m_size += length;
@ -74,7 +107,7 @@ void KBufferBuilder::append(const char* characters, int length)
void KBufferBuilder::append(char ch)
{
if (!can_append(1))
if (!check_expand(1))
return;
insertion_ptr()[0] = ch;
m_size += 1;