Soft links: Initial, incompete implementation

fs/vfs/Make.defs

@@ -1,7 +1,7 @@
 ############################################################################
 # fs/vfs/Make.defs
 #
-#   Copyright (C) 2014-2015 Gregory Nutt. All rights reserved.
+#   Copyright (C) 2014-2015, 2017 Gregory Nutt. All rights reserved.
 #   Author: Gregory Nutt <gnutt@nuttx.org>
 #
 # Redistribution and use in source and binary forms, with or without
@@ -43,7 +43,11 @@ ifneq ($(CONFIG_NSOCKET_DESCRIPTORS),0)
 
 CSRCS += fs_close.c fs_read.c fs_write.c fs_ioctl.c
 
-# Support for network access using streams
+ifneq ($(CONFIG_PSEUDOFS_SOFTLINKS),0)
+CSRCS += fs_softlink.c
+endif
+
+# Stream support
 
 ifneq ($(CONFIG_NFILE_STREAMS),0)
 CSRCS += fs_fdopen.c
@@ -86,6 +90,10 @@ endif
 
 CSRCS += fs_pread.c fs_pwrite.c
 
+ifneq ($(CONFIG_PSEUDOFS_SOFTLINKS),0)
+CSRCS += fs_softlink.c
+endif
+
 # Stream support
 
 ifneq ($(CONFIG_NFILE_STREAMS),0)

fs/vfs/fs_rmdir.c

@@ -84,8 +84,9 @@ int rmdir(FAR const char *pathname)
   const char       *relpath = NULL;
   int               errcode;
 
-  /* Get an inode for this file.  inode_find() automatically increments the
-   * reference count on the inode if one is found.
+  /* Get an inode for the directory (or for the mountpoint containing the
+   * directory).  inode_find() automatically increments the reference count
+   * on the inode if one is found.
    */
 
   inode = inode_find(pathname, &relpath);

fs/vfs/fs_softlink.c

@@ -0,0 +1,169 @@
+/****************************************************************************
+ * fs/vfs/fs_softlink.c
+ *
+ *   Copyright (C) 2017 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 <sys/stat.h>
+#include <errno.h>
+
+#include <nuttx/fs/fs.h>
+
+#include "inode/inode.h"
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+#ifdef CONFIG_PSEUDOFS_SOFTLINKS
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: link
+ *
+ * Description:
+ *   The link() function will create a new link (directory entry) for the
+ *   existing file, path1.  This implementation is simplied for use with
+ *   NuttX in these ways:
+ *
+ *   - Links may be created only within the NuttX top-level, pseudo file
+ *     system.  No file system currently supported by NuttX provides
+ *     symbolic links.
+ *   - For the same reason, only soft links are implemented.
+ *   - File privileges are ignored.
+ *   - c_time is not updated.
+ *
+ * Input Parameters:
+ *   path1 - Points to a pathname naming an existing file.
+ *   path2 - Points to a pathname naming the new directory entry to be created.
+ *
+ * Returned Value:
+ *   On success, zero (OK) is returned.  Otherwise, -1 (ERROR) is returned
+ *   the the errno variable is set appropriately.
+ *
+ ****************************************************************************/
+
+int link(FAR const char *path1, FAR const char *path2)
+{
+  FAR struct inode *inode;
+  int errcode;
+  int ret;
+
+  DEBUGASSERT(path1 != NULL && path2 != NULL && *path2 != '\0');
+
+  /* Check that no inode exists at the 'path2' and that the path up to 'path2'
+   * does not lie on a mounted volume.
+   */
+
+  inode = inode_find(pathname, NULL);
+  if (inode != NULL)
+    {
+#ifndef CONFIG_DISABLE_MOUNTPOINT
+      /* Check if the inode is a mountpoint. */
+
+      if (INODE_IS_MOUNTPT(inode))
+        {
+          /* Symbol links within the mounted volume are not supported */
+
+          errcode = ENOSYS;
+        }
+      else
+#endif
+        {
+          /* A node already exists in the pseudofs at 'path2' */
+
+          errorcode = EEXIST;
+        }
+
+      goto errout_with_inode;
+    }
+
+  /* No inode exists that contains this path.  Create a new inode in the
+   * pseudo-filesystem at this location.
+   */
+
+  else
+    {
+      /* Copy path2 */
+
+      FAR char newpath2 = strdup(path2);
+      if (newpath2 == NULL)
+        {
+          errcode = ENOMEM;
+          goto errout;          
+        }
+
+      /* Create an inode in the pseudo-filesystem at this path.
+       * NOTE that the new inode will be created with a reference
+       * count of zero.
+       */
+
+      inode_semtake();
+      ret = inode_reserve(pathname, &inode);
+      inode_semgive();
+
+      if (ret < 0)
+        {
+          kmm_free(newpath2)
+          errcode = -ret;
+          goto errout;
+        }
+
+      /* Initialize the inode */
+
+      INODE_SET_SOFTLINK(inode);
+      inode->u.i_link = newpath2;
+      inode->i_crefs  = 1;
+    }
+
+  /* Symbolic link successfully created */
+
+  return OK;
+
+errout_with_inode:
+  inode_release(inode);
+errout:
+  set_errno(errcode);
+  return ERROR;
+}
+
+#endif /* CONFIG_PSEUDOFS_SOFTLINKS */