cdrom_id: retry to open the device, if EBUSY

We might fight about the device with polling processes, or other
users who probe the device. Retry a few times if the other one goes
away in the meantime.

Based on a patch from Harald Hoyer.

diff --git a/extras/cdrom_id/cdrom_id.c b/extras/cdrom_id/cdrom_id.c
index 036ef284bf89a25b7783d837a48bba0d3dc6f0c1..7c9f8cc73eb3fee57322b822bd5ac30cef9dca97 100644 (file)
--- a/extras/cdrom_id/cdrom_id.c
+++ b/extras/cdrom_id/cdrom_id.c
@@ -30,6 +30,7 @@
 #include <fcntl.h>
 #include <errno.h>
 #include <getopt.h>
+#include <time.h>
 #include <scsi/sg.h>
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -591,7 +592,22 @@ int main(int argc, char *argv[])
                goto exit;
        }
 
-       fd = open(node, O_RDONLY|O_NONBLOCK|(is_mounted(node) ? 0 : O_EXCL));
+       if (is_mounted(node)) {
+               fd = open(node, O_RDONLY|O_NONBLOCK);
+       } else {
+               int cnt;
+               struct timespec duration;
+
+               srand((unsigned int)getpid());
+               for (cnt = 40; cnt > 0; cnt--) {
+                       fd = open(node, O_RDONLY|O_NONBLOCK|O_EXCL);
+                       if (fd >= 0 || errno != EBUSY)
+                               break;
+                       duration.tv_sec = 0;
+                       duration.tv_nsec = (100 * 1000 * 1000) + (rand() % 100 * 1000 * 1000);
+                       nanosleep(&duration, NULL);
+               }
+       }
        if (fd < 0) {
                info(udev, "unable to open '%s'\n", node);
                fprintf(stderr, "unable to open '%s'\n", node);