consider "fullblock" cmd line arg also for block writes

src/uu/dd/src/dd.rs

@@ -775,6 +775,30 @@ impl<'a> Output<'a> {
         }
     }
 
+    /// writes a block of data. optionally retries when first try didn't complete
+    ///
+    /// this is needed by gnu-test: tests/dd/stats.s
+    /// the write can be interrupted by a system signal.
+    /// e.g. SIGUSR1 which is send to report status
+    /// without retry, the data might not be fully written to destination.
+    fn write_block(&mut self, chunk: &[u8]) -> io::Result<usize> {
+        let full_len = chunk.len();
+        let mut base_idx = 0;
+        loop {
+            match self.dst.write(&chunk[base_idx..]) {
+                Ok(wlen) => {
+                    base_idx += wlen;
+                    // take iflags.fullblock as oflags shall not have this option
+                    if (base_idx >= full_len) || !self.settings.iflags.fullblock {
+                        return Ok(base_idx);
+                    }
+                }
+                Err(e) if e.kind() == io::ErrorKind::Interrupted => continue,
+                Err(e) => return Err(e),
+            }
+        }
+    }
+
     /// Write the given bytes one block at a time.
     ///
     /// This may write partial blocks (for example, if the underlying
@@ -788,7 +812,7 @@ impl<'a> Output<'a> {
         let mut bytes_total = 0;
 
         for chunk in buf.chunks(self.settings.obs) {
-            let wlen = self.dst.write(chunk)?;
+            let wlen = self.write_block(chunk)?;
             if wlen < self.settings.obs {
                 writes_partial += 1;
             } else {