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Kernel: Make DiskBackedFS::read_block() write to client-provided memory

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Instead of having DiskBackedFS allocate a ByteBuffer, leave it to each
client to provide buffer space.

This is significantly faster in many cases where we can use a stack
buffer and avoid heap allocation entirely.
This commit is contained in:
Andreas Kling
2019-09-30 11:04:30 +02:00
parent a61f6ccc27
commit 1fc2612667
3 changed files with 49 additions and 34 deletions
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22
Kernel/FileSystem/DiskBackedFileSystem.cpp
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@@ -107,7 +107,7 @@ bool DiskBackedFS::write_blocks(unsigned index, unsigned count, const ByteBuffer
return true;
}
ByteBuffer DiskBackedFS::read_block(unsigned index) const
bool DiskBackedFS::read_block(unsigned index, u8* buffer) const
{
#ifdef DBFS_DEBUG
kprintf("DiskBackedFileSystem::read_block %u\n", index);
@@ -120,27 +120,25 @@ ByteBuffer DiskBackedFS::read_block(unsigned index) const
entry.has_data = true;
ASSERT(success);
}
return ByteBuffer::copy(entry.data, block_size());
memcpy(buffer, entry.data, block_size());
return true;
}
ByteBuffer DiskBackedFS::read_blocks(unsigned index, unsigned count) const
bool DiskBackedFS::read_blocks(unsigned index, unsigned count, u8* buffer) const
{
if (!count)
return nullptr;
return false;
if (count == 1)
return read_block(index);
auto blocks = ByteBuffer::create_uninitialized(count * block_size());
u8* out = blocks.data();
return read_block(index, buffer);
u8* out = buffer;
for (unsigned i = 0; i < count; ++i) {
auto block = read_block(index + i);
if (!block)
return nullptr;
memcpy(out, block.data(), block.size());
if (!read_block(index + i, out))
return false;
out += block_size();
}
return blocks;
return true;
}
void DiskBackedFS::flush_writes()