drivers/serial/pty.c: Add support so that a PTY can poll for both IN/OUT event simultaneously.

drivers/pipes/pipe_common.c

@@ -1,7 +1,8 @@
 /****************************************************************************
  * drivers/pipes/pipe_common.c
  *
- *   Copyright (C) 2008-2009, 2011, 2015-2016 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2008-2009, 2011, 2015-2016, 2018 Gregory Nutt. All
+ *     rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -721,17 +722,18 @@ int pipecommon_poll(FAR struct file *filep, FAR struct pollfd *fds,
         }
 
       /* Notify the POLLOUT event if the pipe is not full, but only if
-       * there is readers. */
+       * there is readers.
+       */
 
       eventset = 0;
-      if (nbytes < (dev->d_bufsize - 1))
+      if ((filep->f_oflags & O_WROK) && (nbytes < (dev->d_bufsize - 1)))
         {
           eventset |= POLLOUT;
         }
 
       /* Notify the POLLIN event if the pipe is not empty */
 
-      if (nbytes > 0)
+      if ((filep->f_oflags & O_RDOK) && (nbytes > 0))
         {
           eventset |= POLLIN;
         }

drivers/serial/pty.c

@@ -1,7 +1,7 @@
 /****************************************************************************
  * drivers/serial/pty.c
  *
- *   Copyright (C) 2016-2017 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2016-2018 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -112,10 +112,22 @@
 
 #undef CONFIG_PSEUDOTERM_FULLBLOCKS
 
+/* Maximum number of threads than can be waiting for POLL events */
+
+#ifndef CONFIG_DEV_PTY_NPOLLWAITERS
+#  define CONFIG_DEV_PTY_NPOLLWAITERS 2
+#endif
+
 /****************************************************************************
  * Private Types
  ****************************************************************************/
 
+struct pty_poll_s
+{
+  FAR void *src;
+  FAR void *sink;
+};
+
 /* This device structure describes on memory of the PTY device pair */
 
 struct pty_devpair_s;
@@ -132,6 +144,10 @@ struct pty_dev_s
   tcflag_t pd_iflag;            /* Terminal nput modes */
   tcflag_t pd_oflag;            /* Terminal output modes */
 #endif
+
+#ifndef CONFIG_DISABLE_POLL
+  struct pty_poll_s pd_poll[CONFIG_DEV_PTY_NPOLLWAITERS];
+#endif
 };
 
 /* This structure describes the pipe pair */
@@ -160,8 +176,10 @@ static void    pty_semtake(FAR struct pty_devpair_s *devpair);
 static void    pty_destroy(FAR struct pty_devpair_s *devpair);
 #endif
 
+#ifndef CONFIG_DISABLE_PSEUDOFS_OPERATIONS
 static int     pty_open(FAR struct file *filep);
 static int     pty_close(FAR struct file *filep);
+#endif
 static ssize_t pty_read(FAR struct file *filep, FAR char *buffer,
                  size_t buflen);
 static ssize_t pty_write(FAR struct file *filep, FAR const char *buffer,
@@ -922,34 +940,81 @@ static int pty_poll(FAR struct file *filep, FAR struct pollfd *fds,
 {
   FAR struct inode *inode;
   FAR struct pty_dev_s *dev;
+  FAR struct pty_devpair_s *devpair;
+  FAR struct pty_poll_s *pollp = NULL;
   int ret = -ENOSYS;
+  int i;
 
   DEBUGASSERT(filep != NULL && filep->f_inode != NULL);
   inode   = filep->f_inode;
   dev     = inode->i_private;
+  devpair = dev->pd_devpair;
 
-  /* REVISIT: If both POLLIN and POLLOUT are set, might the following logic
+  pty_semtake(devpair);
-   * fail?  Could we not get POLLIN on the sink file and POLLOUT on the source
+
-   * file?
+  if (setup)
-   */
+    {
+      for (i = 0; i < CONFIG_DEV_PTY_NPOLLWAITERS; i++)
+        {
+          if (dev->pd_poll[i].src == NULL && dev->pd_poll[i].sink == NULL)
+            {
+              pollp = &dev->pd_poll[i];
+              break;
+            }
+        }
+
+      if (i >= CONFIG_DEV_PTY_NPOLLWAITERS)
+        {
+          ret = -EBUSY;
+          goto errout;
+        }
+    }
+  else
+    {
+      pollp = (FAR struct pty_poll_s *)fds->priv;
+    }
 
   /* POLLIN: Data other than high-priority data may be read without blocking. */
 
   if ((fds->events & POLLIN) != 0)
     {
+      fds->priv = pollp->src;
       ret = file_poll(&dev->pd_src, fds, setup);
-    }
+      if (ret < 0)
-
-  if (ret >= OK || ret == -ENOTTY)
-    {
-      /* POLLOUT: Normal data may be written without blocking. */
-
-      if ((fds->events & POLLOUT) != 0)
         {
-          ret = file_poll(&dev->pd_sink, fds, setup);
+          goto errout;
         }
+
+      pollp->src = fds->priv;
     }
 
+  /* POLLOUT: Normal data may be written without blocking. */
+
+  if ((fds->events & POLLOUT) != 0)
+    {
+      fds->priv = pollp->sink;
+      ret = file_poll(&dev->pd_sink, fds, setup);
+      if (ret < 0)
+        {
+          if (pollp->src)
+            {
+              fds->priv = pollp->src;
+              file_poll(&dev->pd_src, fds, false);
+              pollp->src = NULL;
+            }
+
+          goto errout;
+        }
+      pollp->sink = fds->priv;
+    }
+
+  if (setup)
+    {
+      fds->priv = pollp;
+    }
+
+errout:
+  pty_semgive(devpair);
   return ret;
 }
 #endif