Improved and documented workaround for udev

README

@@ -92,6 +92,21 @@ Make sure to re-compile all source files after running ./configure
    make install
 
 
+Linux only:
+
+libburn tries to avoid a collision with udev's drive examination by waiting
+0.1 seconds before opening the device file for a longer time, after udev
+might have been alarmed by drive scanning activities.
+The waiting time can be set at ./configure time with microsecond granularity.
+E.g. 2 seconds:
+  CFLAGS="$CFLAGS -DLibburn_udev_wait_useC=2000000"
+  ./configure ...options...
+Closing and re-opening can be disabled by zero waiting time:
+  CFLAGS="$CFLAGS -DLibburn_udev_wait_useC=0"
+Alternatively, libburn can try to be nice by opening the device file,
+closing it immediately, waiting, and only then opening it for real:
+  CFLAGS="$CFLAGS -DLibburn_udev_extra_open_cyclE"
+
 ------------------------------------------------------------------------------
 
 An important part of the project, libisofs, is hosted in a bzr repository at

cdrskin/README

@@ -438,6 +438,22 @@ It will not read startup files, will abort on option  dev_translation= ,
 will not have a fifo buffer, and will not be able to put out help texts or
 debugging messages.
 
+
+Linux only:
+
+libburn tries to avoid a collision with udev's drive examination by waiting
+0.1 seconds before opening the device file for a longer time, after udev
+might have been alarmed by drive scanning activities.
+The waiting time can be set at ./configure time with microsecond granularity.
+E.g. 2 seconds:
+  CFLAGS="$CFLAGS -DLibburn_udev_wait_useC=2000000"
+  ./configure ...options...
+Closing and re-opening can be disabled by zero waiting time:
+  CFLAGS="$CFLAGS -DLibburn_udev_wait_useC=0"
+Alternatively, libburn can try to be nice by opening the device file,
+closing it immediately, waiting, and only then opening it for real:
+  CFLAGS="$CFLAGS -DLibburn_udev_extra_open_cyclE"
+
 ------------------------------------------------------------------------------
 
                   System Dependend Drive Permission Examples

cdrskin/cdrskin_timestamp.h

@@ -1 +1 @@
-#define Cdrskin_timestamP "2011.09.20.132438"
+#define Cdrskin_timestamP "2011.09.21.133344"

libburn/sg-linux.c

@@ -1531,6 +1531,33 @@ int sg_grab(struct burn_drive *d)
 	   relase of drive. Unclear why not the official error return
 	   value -1 of open(2) war used. */
 	if(! burn_drive_is_open(d)) {
+		char msg[120];
+
+#ifndef Libburn_udev_wait_useC
+#define Libburn_udev_wait_useC 100000
+#endif
+
+#ifndef Libburn_udev_extra_open_cyclE
+
+	if (Libburn_udev_wait_useC > 0) {
+		/* ts B10921 : workaround for udev which might get
+				a kernel event from open() and might
+				remove links if it cannot inspect the
+				drive. This waiting period shall allow udev
+				to act after it was woken up by the drive scan
+				activities.
+		*/
+		sprintf(msg,
+	    "To avoid collision with udev: Waiting %lu usec before grabbing",
+				(unsigned long) Libburn_udev_wait_useC);
+		libdax_msgs_submit(libdax_messenger, -1, 0x00000002,
+				LIBDAX_MSGS_SEV_DEBUG, LIBDAX_MSGS_PRIO_HIGH,
+				msg, 0, 0);
+		usleep(Libburn_udev_wait_useC);
+	}
+
+#endif /* Libburn_udev_extra_open_cyclE */
+
 
 try_open:;
 		/* ts A60821
@@ -1553,21 +1580,34 @@ try_open:;
 
 		fd = open(d->devname, open_mode);
 		os_errno = errno;
-		if (fd >= 0) {
+
+#ifdef Libburn_udev_extra_open_cyclE
+
 		/* ts B10920 : workaround for udev which might get
 				a kernel event from open() and might
 				remove links if it cannot inspect the
 				drive.
+		   ts B10921 : this is more obtrusive than above waiting
+				before open(). The drive scan already has
+				opened and closed the drive several times.
+				So it seems to be merely about giving an
+				opportunity to udev, before long term grabbing
+				happens.
 		*/
+		if (fd >= 0 && Libburn_udev_wait_useC > 0) {
+			close(fd);
+			sprintf(msg,
+	    "To avoid collision with udev: Waiting %lu usec before re-opening",
+				(unsigned long) Libburn_udev_wait_useC);
 			libdax_msgs_submit(libdax_messenger, -1, 0x00000002,
 				LIBDAX_MSGS_SEV_DEBUG, LIBDAX_MSGS_PRIO_HIGH,
-			"Waiting 2 seconds to avoid collision with udev",
+				msg, 0, 0);
-				 0, 0);
+			usleep(Libburn_udev_wait_useC);
-			close(fd);
-			usleep(2000000);
 			fd = open(d->devname, open_mode);
 			os_errno = errno;
 		}
+#endif /* Libburn_udev_extra_open_cyclE */
+
 		if (fd >= 0) {
 			sg_fcntl_lock(&fd, d->devname, F_WRLCK, 1);
 			if (fd < 0)
@@ -1591,6 +1631,10 @@ try_open:;
 drive_is_in_use:;
 	tries++;
 	if (tries < max_tries) {
+		libdax_msgs_submit(libdax_messenger, -1, 0x00000002,
+				LIBDAX_MSGS_SEV_DEBUG, LIBDAX_MSGS_PRIO_HIGH,
+			"Drive is in use. Waiting 2 seconds before re-try", 
+				0, 0);
 		usleep(2000000);
 		goto try_open;
 	}