malloc/{memusage.c, memusagestat.c}: fix warn unused result

Fix unused result warnings, detected when _FORTIFY_SOURCE is enabled in
glibc.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

malloc/memusage.c

@@ -18,7 +18,10 @@
 
 #include <assert.h>
 #include <dlfcn.h>
+#include <errno.h>
+#include <error.h>
 #include <fcntl.h>
+#include <libintl.h>
 #include <stdatomic.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -142,6 +145,27 @@ peak_atomic_max (_Atomic size_t *peak, size_t val)
   while (! atomic_compare_exchange_weak (peak, &v, val));
 }
 
+static void
+write_all (int fd, const void *buffer, size_t length)
+{
+  const char *p = buffer;
+  const char *end = p + length;
+  while (p < end)
+    {
+      ssize_t ret = write (fd, p, end - p);
+      if (ret < 0)
+	error (EXIT_FAILURE, errno,
+	       gettext ("write of %zu bytes failed after %td: %m"),
+	       length, p - (const char *) buffer);
+
+      if (ret == 0)
+	error (EXIT_FAILURE, 0,
+	       gettext ("write returned 0 after writing %td bytes of %zu"),
+	       p - (const char *) buffer, length);
+      p += ret;
+    }
+}
+
 /* Update the global data after a successful function call.  */
 static void
 update_data (struct header *result, size_t len, size_t old_len)
@@ -210,10 +234,11 @@ update_data (struct header *result, size_t len, size_t old_len)
       gettime (&buffer[idx]);
 
       /* Write out buffer if it is full.  */
-      if (idx + 1 == buffer_size)
-        write (fd, buffer, buffer_size * sizeof (struct entry));
-      else if (idx + 1 == 2 * buffer_size)
-        write (fd, &buffer[buffer_size], buffer_size * sizeof (struct entry));
+      if (idx + 1 == buffer_size || idx + 1 == 2 * buffer_size)
+        {
+	  uint32_t write_size = buffer_size * sizeof (buffer[0]);
+	  write_all (fd, &buffer[idx + 1 - buffer_size], write_size);
+        }
     }
 }
 
@@ -299,8 +324,8 @@ me (void)
               first.stack = 0;
               gettime (&first);
               /* Write it two times since we need the starting and end time. */
-              write (fd, &first, sizeof (first));
-              write (fd, &first, sizeof (first));
+	      write_all (fd, &first, sizeof (first));
+	      write_all (fd, &first, sizeof (first));
 
               /* Determine the buffer size.  We use the default if the
                  environment variable is not present.  */
@@ -850,24 +875,29 @@ dest (void)
   if (fd != -1)
     {
       /* Write the partially filled buffer.  */
+      struct entry *start = buffer;
+      uint32_t write_cnt = buffer_cnt;
+
       if (buffer_cnt > buffer_size)
-        write (fd, buffer + buffer_size,
-               (buffer_cnt - buffer_size) * sizeof (struct entry));
-      else
-        write (fd, buffer, buffer_cnt * sizeof (struct entry));
+        {
+          start = buffer + buffer_size;
+          write_cnt = buffer_cnt - buffer_size;
+        }
+
+      write_all (fd, start, write_cnt * sizeof (buffer[0]));
 
       /* Go back to the beginning of the file.  We allocated two records
          here when we opened the file.  */
       lseek (fd, 0, SEEK_SET);
       /* Write out a record containing the total size.  */
       first.stack = peak_total;
-      write (fd, &first, sizeof (struct entry));
+      write_all (fd, &first, sizeof (first));
       /* Write out another record containing the maximum for heap and
          stack.  */
       first.heap = peak_heap;
       first.stack = peak_stack;
       gettime (&first);
-      write (fd, &first, sizeof (struct entry));
+      write_all (fd, &first, sizeof (first));
 
       /* Close the file.  */
       close (fd);