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Kernel/FATFS: Only read the requested blocks in read_bytes_locked()
This dramatically improves performance when working with large files, since we no longer re-read the entire file for each read.
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@ -434,19 +434,29 @@ ErrorOr<size_t> FATInode::read_bytes_locked(off_t offset, size_t size, UserOrKer
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if (offset >= m_entry.file_size)
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return 0;
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// FIXME: Read only the needed blocks instead of the whole file
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auto blocks = TRY(const_cast<FATInode&>(*this).read_block_list());
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auto block_list = TRY(const_cast<FATInode&>(*this).get_block_list());
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// Take the minimum of the:
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// 1. User-specified size parameter
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// 2. The file size.
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// 3. The number of blocks returned for reading.
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size_t read_size = min(
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min(size, m_entry.file_size - offset),
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(m_cluster_list.size() * fs().m_device_block_size * fs().m_parameter_block->common_bpb()->sectors_per_cluster) - offset);
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TRY(buffer.write(blocks->data() + offset, read_size));
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u32 first_block_index = offset / fs().m_device_block_size;
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u32 last_block_index = (offset + size - 1) / fs().m_device_block_size;
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return read_size;
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size_t offset_into_first_block = offset - first_block_index * fs().m_device_block_size;
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size_t nread = 0;
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size_t remaining_count = size;
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for (u32 block_index = first_block_index; block_index <= last_block_index; ++block_index) {
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size_t offset_into_block = block_index == first_block_index ? offset_into_first_block : 0;
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size_t to_read = min(fs().m_device_block_size - offset_into_block, remaining_count);
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auto buffer_offset = buffer.offset(nread);
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dbgln_if(FAT_DEBUG, "FATInode[{}]::read_bytes_locked(): Reading {} byte(s) from block {} at offset {}", identifier(), to_read, block_list[block_index], offset_into_block);
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TRY(fs().read_block(block_list[block_index], &buffer_offset, to_read, offset_into_block));
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nread += to_read;
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remaining_count -= to_read;
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}
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return size;
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}
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InodeMetadata FATInode::metadata() const
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