Soft links: Add an (untested) implementation of readlink()

fs/vfs/Make.defs

@@ -87,7 +87,7 @@ endif
 CSRCS += fs_pread.c fs_pwrite.c
 
 ifneq ($(CONFIG_PSEUDOFS_SOFTLINKS),0)
-CSRCS += fs_link.c
+CSRCS += fs_link.c fs_readlink.c
 endif
 
 # Stream support

fs/vfs/fs_readlink.c

@@ -0,0 +1,130 @@
+/****************************************************************************
+ * fs/vfs/fs_readlink.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 will 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 <string.h>
+#include <assert.h>
+#include <errno.h>
+
+#include <nuttx/fs/fs.h>
+
+#include "inode/inode.h"
+
+#ifdef CONFIG_PSEUDOFS_SOFTLINKS
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: mkdir
+ *
+ * Description:
+ *   The readlink() function will place the contents of the symbolic link
+ *   referred to by 'path' in the buffer 'buf' which has size 'bufsize'. If
+ *   the number of bytes in the symbolic link is less than bufsize, the
+ *   contents of the remainder of 'buf' are unspecified. If the buf argument
+ *   is not large enough to contain the link content, the first bufsize bytes
+ *   will be placed in buf.  If the value of bufsize is greater than
+ *   {SSIZE_MAX}, the result is implementation-defined. *
+ *
+ * Input Parameters:
+ *   path   - The full path to the symbolic link
+ *   buf    - The user-provided buffer in which to return the path to the
+ *            link target.
+ *   bufixe - The size of 'buf'
+ *
+ * Returned Value:
+ *   Upon successful completion, readlink() will return the count of bytes
+ *   placed in the buffer. Otherwise, it will return a value of -1, leave the
+ *   buffer unchanged, and set errno to indicate the error.
+ *
+ ****************************************************************************/
+
+ssize_t readlink(FAR const char *path, FAR char *buf, size_t bufsize)
+{
+  FAR struct inode *node;
+  const char *relpath = NULL;
+  int errcode;
+
+  DEBUGASSERT(path != NULL && buf != NULL && bufsize > 0);
+
+  /* Find the inode that includes this path (without derefencing the final)
+   * symbolic link node.
+   */
+
+  node = inode_find(path, &relpath);
+  if (node == NULL)
+    {
+      errcode = ENOENT;
+      goto errout;
+    }
+
+  /* An inode was found that includes this path and possibly refers to a
+   * symbolic link.
+   *
+   * Check if the inode is a valid symbolic link.
+   */
+
+  if (!INODE_IS_SOFTLINK(node))
+    {
+      errcode = EINVAL;
+      goto errout_with_inode;
+    }
+
+  /* Copy the link target pathto the user-provided buffer. */
+
+  *buf = '\0';
+  (void)strncpy(node->u.i_link, buf, bufsize);
+
+  /* Release our reference on the inode and return the length */
+
+  inode_release(node);
+  return strlen(buf);
+
+errout_with_inode:
+  inode_release(node);
+errout:
+  set_errno(errcode);
+  return ERROR;
+}
+
+#endif /* CONFIG_PSEUDOFS_SOFTLINKS */

include/sys/syscall.h

@@ -325,7 +325,8 @@
 
 #  if defined(CONFIG_PSEUDOFS_SOFTLINKS)
 #    define SYS_link                   (__SYS_filedesc+14)
-#    define __SYS_pipes                (__SYS_filedesc+15)
+#    define SYS_readlink               (__SYS_filedesc+15)
+#    define __SYS_pipes                (__SYS_filedesc+16)
 #  else
 #    define __SYS_pipes                (__SYS_filedesc+14)
 #  endif

include/unistd.h

@@ -190,7 +190,11 @@ FAR char *getcwd(FAR char *buf, size_t size);
 int     access(FAR const char *path, int amode);
 int     rmdir(FAR const char *pathname);
 int     unlink(FAR const char *pathname);
+
+#ifdef CONFIG_PSEUDOFS_SOFTLINKS
 int     link(FAR const char *path1, FAR const char *path2);
+ssize_t readlink(FAR const char *path, FAR char *buf, size_t bufsize);
+#endif
 
 /* Execution of programs from files */
 

syscall/syscall.csv

@@ -99,6 +99,7 @@
 "putenv","stdlib.h","!defined(CONFIG_DISABLE_ENVIRON)","int","FAR const char*"
 "read","unistd.h","CONFIG_NSOCKET_DESCRIPTORS > 0 || CONFIG_NFILE_DESCRIPTORS > 0","ssize_t","int","FAR void*","size_t"
 "readdir","dirent.h","CONFIG_NFILE_DESCRIPTORS > 0","FAR struct dirent*","FAR DIR*"
+"readlink","unistd.h","defined(CONFIG_PSEUDOFS_SOFTLINKS)","ssize_t","FAR const char *","FAR char *","size_t"
 "recv","sys/socket.h","CONFIG_NSOCKET_DESCRIPTORS > 0 && defined(CONFIG_NET)","ssize_t","int","FAR void*","size_t","int"
 "recvfrom","sys/socket.h","CONFIG_NSOCKET_DESCRIPTORS > 0 && defined(CONFIG_NET)","ssize_t","int","FAR void*","size_t","int","FAR struct sockaddr*","FAR socklen_t*"
 "rename","stdio.h","CONFIG_NFILE_DESCRIPTORS > 0 && !defined(CONFIG_DISABLE_MOUNTPOINT)","int","FAR const char*","FAR const char*"

syscall/syscall_lookup.h

@@ -234,6 +234,7 @@ SYSCALL_LOOKUP(up_assert,                 2, STUB_up_assert)
 
 #  if defined(CONFIG_PSEUDOFS_SOFTLINKS)
   SYSCALL_LOOKUP(link,                    2, STUB_link)
+  SYSCALL_LOOKUP(readlink,                3, STUB_readlink)
 #  endif
 
 #  if defined(CONFIG_PIPES) && CONFIG_DEV_PIPE_SIZE > 0

syscall/syscall_stublookup.c

@@ -239,6 +239,8 @@ uintptr_t STUB_statfs(int nbr, uintptr_t parm1, uintptr_t parm2);
 uintptr_t STUB_telldir(int nbr, uintptr_t parm1);
 
 uintptr_t STUB_link(int nbr, uintptr_t parm1, uintptr_t parm2);
+uintptr_t STUB_readlink(int nbr, uintptr_t parm1, uintptr_t parm2,
+            uintptr_t parm3);
 
 uintptr_t STUB_pipe2(int nbr, uintptr_t parm1, uintptr_t parm2);
 uintptr_t STUB_mkfifo2(int nbr, uintptr_t parm1, uintptr_t parm2,