[xiph-cvs] cvs commit: ao/src/plugins/oss ao_oss.c

[Stan Seibert]

volsung     01/08/12 08:12:45

  Modified:    src/plugins/oss ao_oss.c
  Log:
  Changed the way we open the dsp to prevent deadlock if another program
  opens the dsp between plugin_test() and plugin_open().  Now we always
  open it with O_NONBLOCK and remove the blocking later if needed.  The
  ALSA docs claim that this is required by the OSS spec, but that is
  not so obvious.

Revision  Changes    Path
1.10      +35 -17    ao/src/plugins/oss/ao_oss.c

Index: ao_oss.c
===================================================================
RCS file: /usr/local/cvsroot/ao/src/plugins/oss/ao_oss.c,v
retrieving revision 1.9
retrieving revision 1.10
diff -u -r1.9 -r1.10
--- ao_oss.c	2001/08/10 00:32:20	1.9
+++ ao_oss.c	2001/08/12 15:12:45	1.10
@@ -68,39 +68,57 @@
  * open either the devfs device or the traditional device and return a
  * file handle.  Also strdup() path to the selected device into
  * *dev_path.  Assumes that *dev_path does not need to be free()'ed
- * initially.  The extra_open_flags allows additional flags to be
- * passed to open() if needed.
+ * initially.
+ *
+ * This opens the device in non-blocking mode at first in order to prevent
+ * deadlock caused by ALSA's OSS emulation and some OSS drivers if the
+ * device is already in use.  If blocking is non-zero, we remove the blocking
+ * flag if possible so that the device can be used for actual output.
  */
-int _open_default_oss_device (char **dev_path, int extra_open_flags)
+int _open_default_oss_device (char **dev_path, int blocking)
 {
         int fd;
+	char *err = NULL;
+	char *dev = NULL;
 
         /* default: first try the devfs path */
         *dev_path = strdup("/dev/sound/dsp");
-	fd = open(*dev_path, O_WRONLY | extra_open_flags);
+	fd = open(*dev_path, O_WRONLY | O_NONBLOCK);
 
+	/* then try the original dsp path */
         if(fd < 0) 
         {
                 /* no? then try the traditional path */
-		char *err = strdup(strerror(errno));
-		char *dev = strdup(*dev_path);
+		err = strdup(strerror(errno));
+		dev = strdup(*dev_path);
                 free(*dev_path);
                 *dev_path = strdup("/dev/dsp");
-		fd = open(*dev_path, O_WRONLY | extra_open_flags);
+		fd = open(*dev_path, O_WRONLY | O_NONBLOCK);
+	}
+
+	/* Now have to remove the O_NONBLOCK flag if so instructed. */
+	if (fd > 0 && blocking) {
+		if (fcntl(fd, F_SETFL, 0) < 0) { /* Remove O_NONBLOCK */
+			/* If we can't go to blocking mode, we can't use
+			   this device */
+			close(fd);
+			fd = -1;
+		}
+	}
 
-		if(fd < 0) 
-		{
-		  /*			fprintf(stderr,
+	/* Deal with error cases */
+	if(fd < 0) 
+	{
+	  /*			fprintf(stderr,
                                 "libao - error: Could not open either default device:\n"
                                 "  %s - %s\n"
                                 "  %s - %s\n",
                                 err, dev,
                                 strerror(errno), *dev_path); */
-			free(err);
-			free(dev);
-			free(*dev_path);
-			*dev_path = NULL;
-		}
+		free(err);
+		free(dev);
+		free(*dev_path);
+		*dev_path = NULL;
         }
 
         return fd;
@@ -117,7 +135,7 @@
            driver detection unless the O_NONBLOCK flag is passed to 
            open().  We cannot use this flag when we actually open the
            device for writing because then we will overflow the buffer. */
-	if ( (fd = _open_default_oss_device(&dev_path, O_NONBLOCK)) < 0 )
+	if ( (fd = _open_default_oss_device(&dev_path, 0)) < 0 )
                 return 0; /* Cannot use this plugin with default parameters */
         else {
                 free(dev_path);
@@ -185,7 +203,7 @@
                 }
 
         } else {
-		internal->fd = _open_default_oss_device(&internal->dev, 0);
+		internal->fd = _open_default_oss_device(&internal->dev, 1);
                 if (internal->fd < 0)
                         return 0;  /* Cannot open default device */
         }

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