Function collect_extents

vmm/src/memory_manager.rs:3330–3342

(
        fd: BorrowedFd<'_>,
        start: u64,
        end: u64,
    )

    }

    fn collect_extents(
        fd: BorrowedFd<'_>,
        start: u64,
        end: u64,
    ) -> std::io::Result<Vec<(u64, u64)>> {
        let mut out = Vec::new();
        let mut cursor = start;
        while let Some((off, len)) = next_data_extent(fd, cursor, end)? {
            out.push((off, len));
            cursor = off + len;
        }
        Ok(out)
    }

    /// Punch an explicit hole into `f`. Tests use this instead of relying on
    /// "didn't write here" to mean "is a hole": modern shmem/tmpfs may