Provide read_buf and read_vectored for Hermit

Author: thaliaarchi

library/std/src/sys/pal/hermit/fd.rs

@@ -2,7 +2,7 @@
 
 use super::hermit_abi;
 use crate::cmp;
-use crate::io::{self, IoSlice, IoSliceMut, Read};
+use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut, Read};
 use crate::os::hermit::io::{FromRawFd, OwnedFd, RawFd, *};
 use crate::sys::{cvt, unsupported};
 use crate::sys_common::{AsInner, FromInner, IntoInner};
@@ -23,6 +23,18 @@ impl FileDesc {
         Ok(result as usize)
     }
 
+    pub fn read_buf(&self, mut buf: BorrowedCursor<'_>) -> io::Result<()> {
+        let result = cvt(unsafe {
+            hermit_abi::read(
+                self.fd.as_raw_fd(),
+                buf.as_mut().as_mut_ptr() as *mut u8,
+                buf.capacity(),
+            )
+        })?;
+        unsafe { buf.advance_unchecked(result as usize) };
+        Ok(())
+    }
+
     pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         let ret = cvt(unsafe {
             hermit_abi::readv(

library/std/src/sys/pal/hermit/fs.rs

@@ -400,7 +400,7 @@ impl File {
     }
 
     pub fn read_buf(&self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
-        crate::io::default_read_buf(|buf| self.read(buf), cursor)
+        self.0.read_buf(cursor)
     }
 
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {

library/std/src/sys/pal/hermit/stdio.rs

@@ -1,6 +1,6 @@
 use super::hermit_abi;
 use crate::io;
-use crate::io::{IoSlice, IoSliceMut};
+use crate::io::{BorrowedCursor, IoSlice, IoSliceMut};
 use crate::mem::ManuallyDrop;
 use crate::os::hermit::io::FromRawFd;
 use crate::sys::fd::FileDesc;
@@ -20,6 +20,10 @@ impl io::Read for Stdin {
         unsafe { ManuallyDrop::new(FileDesc::from_raw_fd(hermit_abi::STDIN_FILENO)).read(buf) }
     }
 
+    fn read_buf(&mut self, buf: BorrowedCursor<'_>) -> io::Result<()> {
+        unsafe { ManuallyDrop::new(FileDesc::from_raw_fd(hermit_abi::STDIN_FILENO)).read_buf(buf) }
+    }
+
     fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
         unsafe {
             ManuallyDrop::new(FileDesc::from_raw_fd(hermit_abi::STDIN_FILENO)).read_vectored(bufs)