lib: Add libusb allocation helper

doc/libfprint-docs.xml

@@ -42,6 +42,7 @@
     <xi:include href="xml/fpi-dev.xml"/>
     <xi:include href="xml/fpi-ssm.xml"/>
     <xi:include href="xml/fpi-poll.xml"/>
+    <xi:include href="xml/fpi-usb.xml"/>
   </part>
 
   <index id="api-index">

doc/libfprint-sections.txt

@@ -193,3 +193,9 @@ FP_IMG_DEV
 fp_dev_set_instance_data
 FP_INSTANCE_DATA
 </SECTION>
+
+<SECTION>
+<INCLUDE>fpi-usb.h</INCLUDE>
+<FILE>fpi-usb</FILE>
+fpi_usb_alloc
+</SECTION>

libfprint/drivers_api.h

@@ -27,13 +27,13 @@
 #include <string.h>
 #include <stdlib.h>
 #include <glib.h>
-#include <libusb.h>
 
 #include "fprint.h"
 #include "fpi-log.h"
 #include "fpi-ssm.h"
 #include "fpi-poll.h"
 #include "fpi-dev.h"
+#include "fpi-usb.h"
 #include "assembling.h"
 #include "drivers/driver_ids.h"
 

libfprint/fpi-usb.c

@@ -0,0 +1,77 @@
+/*
+ * Driver API definitions
+ * Copyright (C) 2018 Bastien Nocera <hadess@hadess.net>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "fpi-usb.h"
+
+/**
+ * SECTION:fpi-usb
+ * @title: Helpers for libusb
+ *
+ * A collection of [libusb helpers](http://libusb.sourceforge.net/api-1.0/group__poll.html#details)
+ * to make driver development easier. Please refer to the libusb API documentation for more
+ * information about the original API.
+ */
+
+/* Helpers from glib */
+#include <glib.h>
+#include <glib/gprintf.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+/* special helpers to avoid gmessage.c dependency */
+static void mem_error (const char *format, ...) G_GNUC_PRINTF (1,2);
+#define mem_assert(cond)    do { if (G_LIKELY (cond)) ; else mem_error ("assertion failed: %s", #cond); } while (0)
+
+static void
+mem_error (const char *format,
+           ...)
+{
+  const char *pname;
+  va_list args;
+  /* at least, put out "MEMORY-ERROR", in case we segfault during the rest of the function */
+  fputs ("\n***MEMORY-ERROR***: ", stderr);
+  pname = g_get_prgname();
+  g_fprintf (stderr, "%s[%ld]: ", pname ? pname : "", (long)getpid());
+  va_start (args, format);
+  g_vfprintf (stderr, format, args);
+  va_end (args);
+  fputs ("\n", stderr);
+  abort();
+  _exit (1);
+}
+
+/**
+ * fpi_usb_alloc:
+ *
+ * Returns a struct libusb_transfer, similar to calling
+ * `libusb_alloc_transfer(0)`[[1](http://libusb.sourceforge.net/api-1.0/group__asyncio.html#ga13cc69ea40c702181c430c950121c000)]. As libfprint uses GLib internally,
+ * and [memory allocation failures will make applications fail](https://developer.gnome.org/glib/stable/glib-Memory-Allocation.html#glib-Memory-Allocation.description),
+ * this helper will assert when the libusb call fails.
+ */
+struct libusb_transfer *
+fpi_usb_alloc(void)
+{
+	struct libusb_transfer *transfer;
+
+	transfer = libusb_alloc_transfer(0);
+	mem_assert(transfer);
+
+	return transfer;
+}

libfprint/fpi-usb.h

@@ -0,0 +1,27 @@
+/*
+ * Driver API definitions
+ * Copyright (C) 2018 Bastien Nocera <hadess@hadess.net>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef __FPI_USB_H__
+#define __FPI_USB_H__
+
+#include <libusb.h>
+
+struct libusb_transfer *fpi_usb_alloc(void) __attribute__((returns_nonnull));
+
+#endif

libfprint/meson.build

@@ -11,6 +11,8 @@ libfprint_sources = [
     'fpi-ssm.h',
     'fpi-poll.h',
     'fpi-poll.c',
+    'fpi-usb.h',
+    'fpi-usb.c',
     'img.c',
     'imgdev.c',
     'sync.c',