Wait for device to disappear after reboot-bootloader.

(Linux only for now) With fastboot reading serial numbers from sysfs, it had
become possible for a fastboot command issued immediately after rebooting
the bootloader to fail, because sysfs still thought the device was online.
To prevent this, after reboot-bootloader we wait for the device to disconnect.

Also made usb_read and usb_write fail immediately if the descriptor has been
closed; this prevents an incorrect error message ("Bad file descriptor")
when errors from fb_getvar are ignored (e.g., by fb_format_supported).

Also removed unused fd param from filter_usb_device, and simplified logic
in usb_write by using do/while instead of a special case for len == 0.

Change-Id: I799b857eab411fd8ad25f5777fc61c685152ea86
diff --git a/fastboot/util.c b/fastboot/util.c
new file mode 100644
index 0000000..f2bbd34
--- /dev/null
+++ b/fastboot/util.c
@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <sys/time.h>
+
+#include "fastboot.h"
+
+double now()
+{
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    return (double)tv.tv_sec + (double)tv.tv_usec / 1000000;
+}
+
+char *mkmsg(const char *fmt, ...)
+{
+    char buf[256];
+    char *s;
+    va_list ap;
+
+    va_start(ap, fmt);
+    vsprintf(buf, fmt, ap);
+    va_end(ap);
+
+    s = strdup(buf);
+    if (s == 0) die("out of memory");
+    return s;
+}
+
+void die(const char *fmt, ...)
+{
+    va_list ap;
+    va_start(ap, fmt);
+    fprintf(stderr,"error: ");
+    vfprintf(stderr, fmt, ap);
+    fprintf(stderr,"\n");
+    va_end(ap);
+    exit(1);
+}