Didn't commit some file previously

Author: tiif

src/shims/unix/socket.rs

@@ -111,6 +111,16 @@ impl FileDescription for SocketPair {
             return Ok(Ok(0));
         }
 
+        // In libc socketpair, reading from a previously full socketpair buffer won't trigger
+        // epoll notification. We want to inform the user about this inconsistency in libc and
+        // hope to receive a bug report if someone has a use case for this.
+        if readbuf.buf.len() == MAX_SOCKETPAIR_BUFFER_CAPACITY {
+            throw_unsup_format!(
+                "A previously full socketpair has been read, please submit a \
+            bug report in https://github.com/rust-lang/miri/issues/new"
+            );
+        }
+
         if readbuf.buf.is_empty() {
             if !readbuf.buf_has_writer {
                 // Socketpair with no writer and empty buffer.

tests/fail-dep/tokio/read_from_full_socketpair.rs

@@ -0,0 +1,16 @@
+fn main() {
+    // Open a socketpair instance.
+    let mut fds = [-1, -1];
+    let mut res =
+        unsafe { libc::socketpair(libc::AF_UNIX, libc::SOCK_STREAM, 0, fds.as_mut_ptr()) };
+    assert_eq!(res, 0);
+
+    // Write until the buffer is full
+    let array = &[0_u8; 212992];
+    let data = array.as_slice().as_ptr();
+    res = unsafe { libc::write(fds[0], data as *const libc::c_void, 212992).try_into().unwrap() };
+    assert_eq!(res, 212992);
+    let mut buf: [u8; 5] = [0; 5];
+    unsafe { libc::read(fds[1], buf.as_mut_ptr().cast(), buf.len() as libc::size_t) };
+    //~^ERROR: A previously full socketpair has been read
+}

tests/fail-dep/tokio/read_from_full_socketpair.stderr

@@ -0,0 +1,14 @@
+error: unsupported operation: A previously full socketpair has been read, please submit a bug report in https://github.com/rust-lang/miri/issues/new
+  --> $DIR/read_from_full_socketpair.rs:LL:CC
+   |
+LL |     unsafe { libc::read(fds[1], buf.as_mut_ptr().cast(), buf.len() as libc::size_t) };
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ A previously full socketpair has been read, please submit a bug report in https://github.com/rust-lang/miri/issues/new
+   |
+   = help: this is likely not a bug in the program; it indicates that the program performed an operation that Miri does not support
+   = note: BACKTRACE:
+   = note: inside `main` at $DIR/read_from_full_socketpair.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+