hw/core/loader.c: Read as long as possible in load_image_size()

Don't expect read(2) can always read as many as it's told.

CC: Richard Henderson <richard.henderson@linaro.org>
CC: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: NLi Zhijian <lizhijian@cn.fujitsu.com>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Reviewed-by: NStefano Garzarella <sgarzare@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/core/loader.c

@@ -77,21 +77,20 @@ int64_t get_image_size(const char *filename)
 ssize_t load_image_size(const char *filename, void *addr, size_t size)
 {
     int fd;
-    ssize_t actsize;
+    ssize_t actsize, l = 0;
 
     fd = open(filename, O_RDONLY | O_BINARY);
     if (fd < 0) {
         return -1;
     }
 
-    actsize = read(fd, addr, size);
-    if (actsize < 0) {
-        close(fd);
-        return -1;
+    while ((actsize = read(fd, addr + l, size - l)) > 0) {
+        l += actsize;
     }
+
     close(fd);
 
-    return actsize;
+    return actsize < 0 ? -1 : l;
 }
 
 /* read()-like version */