Update the libc backend's read to use Buffer.

Author: sunfishcode

src/backend/libc/io/syscalls.rs

@@ -18,19 +18,18 @@ use crate::io::ReadWriteFlags;
 use crate::io::{self, FdFlags};
 use crate::ioctl::{IoctlOutput, RawOpcode};
 use core::cmp::min;
-use core::mem::MaybeUninit;
 #[cfg(not(any(target_os = "espidf", target_os = "horizon")))]
 use {
     crate::backend::MAX_IOV,
     crate::io::{IoSlice, IoSliceMut},
 };
 
-pub(crate) fn read(fd: BorrowedFd<'_>, buf: &mut [MaybeUninit<u8>]) -> io::Result<usize> {
+pub(crate) unsafe fn read(fd: BorrowedFd<'_>, buf: (*mut u8, usize)) -> io::Result<usize> {
     unsafe {
         ret_usize(c::read(
             borrowed_fd(fd),
-            buf.as_mut_ptr().cast(),
-            min(buf.len(), READ_LIMIT),
+            buf.0.cast(),
+            min(buf.1, READ_LIMIT),
         ))
     }
 }