Function encoded_read 

pub fn encoded_read(
    fd: BorrowedFd<'_>,
    buf: &mut [u8],
    offset: u64,
    len: u64,
) -> Result<EncodedReadResult>

Read compressed (encoded) data from a file using BTRFS_IOC_ENCODED_READ.

This reads the raw compressed extent data without decompressing it, which is the counterpart to encoded_write. The caller provides a buffer to receive the data; the returned EncodedReadResult describes the encoding and how many bytes were read.

Errors: ENOTTY on kernels that do not support encoded reads (pre-5.18). EINVAL if the offset or length are not accepted.