Prototype versions of ptmx/pty suppoprt. Still under developement; not yet hooked into build or configuration system.

drivers/serial/ptmx.c

@@ -0,0 +1,330 @@
+/****************************************************************************
+ * drivers/serial/ptmx.c
+ *
+ *   Copyright (C) 2016 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <sys/types.h>
+#include <stdbool.h>
+#include <string.h>
+#include <poll.h>
+#include <errno.h>
+#include <nuttx/fs/fs.h>
+
+/****************************************************************************
+ * Private Function Prototypes
+ ****************************************************************************/
+
+#ifndef CONFIG_PTY_MAXPTY
+#  define CONFIG_PTY_MAXPTY 32
+#endif
+
+#if CONFIG_PTY_MAXPTY > 256
+#  define CONFIG_PTY_MAXPTY 256
+#endif
+
+#define PTY_MAX   ((CONFIG_PTY_MAXPTY + 31) & ~31)
+#define INDEX_MAX (PTY_MAX >> 5)
+
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+
+/* PTMX device state */
+
+struct ptmx_dev_s
+{
+  uint8_t px_next;                  /* Next minor number to allocate */
+  sem_t px_exclsem;                 /* Supports mutual exclusion */
+  uint32_t px_alloctab[INDEX_MAX];  /* Set of allocated PTYs */
+};
+
+/****************************************************************************
+ * Private Function Prototypes
+ ****************************************************************************/
+
+static int     ptmx_open(FAR struct file *filep);
+static ssize_t ptmx_read(FAR struct file *filep, FAR char *buffer,
+                 size_t buflen);
+static ssize_t ptmx_write(FAR struct file *filep, FAR const char *buffer,
+                 size_t buflen);
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+static const struct file_operations g_ptmx_fops =
+{
+  ptmx_open,     /* open */
+  NULL,          /* close */
+  ptmx_read,     /* read */
+  ptmx_write,    /* write */
+  NULL,          /* seek */
+  NULL           /* ioctl */
+#ifndef CONFIG_DISABLE_POLL
+  , NULL         /* poll */
+#endif
+#ifndef CONFIG_DISABLE_PSEUDOFS_OPERATIONS
+  , NULL         /* unlink */
+#endif
+};
+
+static struct ptmx_dev_s g_ptmx;
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: ptmx_semtake and ptmx_semgive
+ *
+ * Description:
+ *   This is just a wrapper to handle the annoying behavior of semaphore
+ *   waits that return due to the receipt of a signal.
+ *
+ ****************************************************************************/
+
+static void ptmx_semtake(void)
+{
+  /* Take the semaphore (perhaps waiting) */
+
+  while (sem_wait(&g_ptmx.px_exclsem) != 0)
+    {
+      /* The only case that an error should occur here is if the wait was
+       * awakened by a signal.
+       */
+
+      DEBUGASSERT(errno == EINTR);
+    }
+}
+
+#define ptmx_semgive() sem_post(&g_ptmx.px_exclsem)
+
+/****************************************************************************
+ * Name: ptmx_minor_allocate
+ *
+ * Description:
+ *   Allocate a new unique PTY minor number.
+ *
+ * Assumptions:
+ *   Caller hold the px_exclsem
+ *
+ ****************************************************************************/
+
+static int ptmx_minor_allocate(FAR struct ptmx_dev_s *ptmx)
+{
+  uint8_t startaddr = g_ptmx.px_next;
+  uint8_t minor;
+  int index;
+  int bitno;
+
+  /* Loop until we find a valid device address */
+
+  for (; ; )
+    {
+      /* Try the next device address */
+
+      minor = g_ptmx.px_next;
+      if (g_ptmx.px_next >= PTY_MAX)
+        {
+          g_ptmx.px_next = 0;
+        }
+      else
+        {
+          g_ptmx.px_next++;
+        }
+
+      /* Is this address already allocated? */
+
+      index = minor >> 5;
+      bitno = minor & 31;
+      if ((g_ptmx.px_alloctab[index] & (1 << bitno)) == 0)
+        {
+          /* No... allocate it now */
+
+          g_ptmx.px_alloctab[index] |= (1 << bitno);
+          return (int)minor;
+        }
+
+      /* This address has already been allocated.  The following logic will
+       * prevent (unexpected) infinite loops.
+       */
+
+      if (startaddr == minor)
+        {
+          /* We are back where we started... the are no free device address */
+
+          return -ENOMEM;
+        }
+    }
+}
+
+/****************************************************************************
+ * Name: ptmx_minor_free
+ *
+ * Description:
+ *   De-allocate a PTY minor number.
+ *
+ * Assumptions:
+ *   Caller hold the px_exclsem
+ *
+ ****************************************************************************/
+
+static void ptmx_minor_free(uint8_t minor)
+{
+  int index;
+  int bitno;
+
+  /* Free the address by clearing the associated bit in the px_alloctab[]; */
+
+  index = minor >> 5;
+  bitno = minor & 31;
+
+  DEBUGASSERT((g_ptmx.px_alloctab[index] |= (1 << bitno)) != 0);
+  g_ptmx.px_alloctab[index] &= ~(1 << bitno);
+
+  /* Reset the next pointer if the one just released has a lower value */
+
+  if (minor < g_ptmx.px_next)
+    {
+      g_ptmx.px_next = minor;
+    }
+}
+
+/****************************************************************************
+ * Name: ptmx_open
+ ****************************************************************************/
+
+static int ptmx_open(FAR struct file *filep)
+{
+  char devname[16];
+  int minor;
+  int fd;
+  int ret;
+
+  /* Get exclusive access */
+
+  ptmx_semtake();
+
+  /* Allocate a PTY minor */
+
+  minor = ptmx_minor_allocate();
+  if (minor < 0)
+    {
+      ret = minor;
+      goto errout_with_sem;
+    }
+
+  /* Create the master slave pair */
+
+  ret = pty_register(minor);
+  if (ret < 0)
+    {
+      goto errout_with_minor;
+    }
+
+  /* Open the master side */
+
+  snprintf(devname, 16, "/dev/ttyp%d", minor);
+  fd = open(devname, O_RDWR);
+  DEBUGASSERT(fd >= 0);  /* open() should never fail */
+
+  /* No unlink the master.  This will remove it from the VFS namespace,
+   * the the driver will still persist because of the open count on the
+   * driver.
+   */
+
+  ret = unlink(devname);
+  DEBUGASSERT(ret >= 0);  /* unlink() should never fail */
+  UNUSED(ret);
+
+  /* Return the master file descriptor */
+
+  ptmx_semgive();
+  return fd;
+
+errout_with_minor:
+  ptmx_minor_free(minor);
+
+errout_with_sem:
+  ptmx_semgive();
+  return ret;
+}
+
+/****************************************************************************
+ * Name: ptmx_read
+ ****************************************************************************/
+
+static ssize_t ptmx_read(FAR struct file *filep, FAR char *buffer, size_t len)
+{
+  return 0; /* Return EOF */
+}
+
+/****************************************************************************
+ * Name: ptmx_write
+ ****************************************************************************/
+
+static ssize_t ptmx_write(FAR struct file *filep, FAR const char *buffer, size_t len)
+{
+  return len; /* Say that everything was written */
+}
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: ptmx_register
+ *
+ * Description:
+ *   Register /dev/null
+ *
+ ****************************************************************************/
+
+void ptmx_register(void)
+{
+  FAR struct ptmx_dev_s *ptmx;
+
+  /* Initialize driver state */
+
+  sem_init(&g_ptmx.px_exclsem, 0, 1);
+
+  /* Register the PTMX driver */
+
+  (void)register_driver("/dev/ptmx", &g_ptmx_fops, 0666, NULL);
+}