4lDO2
48 lines
2.0 KiB
Rust
48 lines
2.0 KiB
Rust
pub fn read<E>(offset: u64, blksize: u32, mut buf: &mut [u8], block_bytes: &mut [u8], mut read: impl FnMut(u64, &mut [u8]) -> Result<(), E>) -> Result<usize, E> {
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// TODO: Yield sometimes, perhaps after a few blocks or something.
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use std::ops::{Add, Div, Rem};
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fn div_round_up<T>(a: T, b: T) -> T
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where
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T: Add<Output = T> + Div<Output = T> + Rem<Output = T> + PartialEq + From<u8> + Copy
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{
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if a % b != T::from(0u8) {
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a / b + T::from(1u8)
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} else {
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a / b
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}
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}
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let orig_buf_len = buf.len();
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let start_block = offset / u64::from(blksize);
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let end_block = div_round_up(offset + buf.len() as u64, u64::from(blksize)); // The first block not in the range
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let offset_from_start_block: u64 = offset % u64::from(blksize);
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let offset_to_end_block: u64 = u64::from(blksize) - (offset + buf.len() as u64) % u64::from(blksize);
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let first_whole_block = start_block + if offset_from_start_block > 0 { 1 } else { 0 };
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let last_whole_block = end_block - if offset_to_end_block > 0 { 1 } else { 0 } - 1;
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let whole_blocks_to_read = last_whole_block - first_whole_block + 1;
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for block in start_block..=end_block {
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// TODO: Async/await? I mean, shouldn't AHCI be async?
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read(block, block_bytes)?;
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let (bytes_to_read, src_buf): (u64, &[u8]) = if block == start_block {
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(u64::from(blksize) - offset_from_start_block, &block_bytes[offset_from_start_block as usize..])
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} else if block == end_block {
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(u64::from(blksize) - offset_to_end_block, &block_bytes[..offset_to_end_block as usize])
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} else {
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(blksize.into(), &block_bytes[..])
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};
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let bytes_to_read = std::cmp::min(bytes_to_read as usize, buf.len());
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buf[..bytes_to_read].copy_from_slice(&src_buf[..bytes_to_read]);
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buf = &mut buf[bytes_to_read..];
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}
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Ok(std::cmp::min(orig_buf_len, whole_blocks_to_read as usize * blksize as usize + offset_from_start_block as usize + offset_to_end_block as usize))
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}
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