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43f0070582
nuttx/fs/inode/fs_inodesearch.c
Xiang Xiao 43f0070582 fs: Simplify the symbol link process in inode_search 
avoid the recursive call by moving the path catenation into _inode_search

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
2020-09-22 16:39:47 +08:00

541 lines
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/****************************************************************************
* fs/inode/fs_inodesearch.c
*
* Copyright (C) 2007-2009, 2011-2012, 2016-2017 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 <stdio.h>
#include <string.h>
#include <limits.h>
#include <assert.h>
#include <errno.h>
#include <nuttx/fs/fs.h>
#include "inode/inode.h"
/****************************************************************************
* Private Function Prototypes
****************************************************************************/
static int _inode_compare(FAR const char *fname, FAR struct inode *node);
#ifdef CONFIG_PSEUDOFS_SOFTLINKS
static int _inode_linktarget(FAR struct inode *node,
FAR struct inode_search_s *desc);
#endif
static int _inode_search(FAR struct inode_search_s *desc);
/****************************************************************************
* Public Data
****************************************************************************/
FAR struct inode *g_root_inode = NULL;
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: _inode_compare
*
* Description:
* Compare two inode names
*
****************************************************************************/
static int _inode_compare(FAR const char *fname, FAR struct inode *node)
{
char *nname = node->i_name;
if (!nname)
{
return 1;
}
if (!fname)
{
return -1;
}
for (; ; )
{
/* At the end of the node name? */
if (!*nname)
{
/* Yes.. also at the end of find name? */
if (!*fname || *fname == '/')
{
/* Yes.. return match */
return 0;
}
else
{
/* No... return find name > node name */
return 1;
}
}
/* At end of the find name? */
else if (!*fname || *fname == '/')
{
/* Yes... return find name < node name */
return -1;
}
/* Check for non-matching characters */
else if (*fname > *nname)
{
return 1;
}
else if (*fname < *nname)
{
return -1;
}
/* Not at the end of either string and all of the
* characters still match. keep looking.
*/
else
{
fname++;
nname++;
}
}
}
/****************************************************************************
* Name: _inode_linktarget
*
* Description:
* If the inode is a soft link, then (1) recursively look-up the inode
* referenced by the soft link, and (2) return the inode referenced by
* the soft link.
*
* Assumptions:
* The caller holds the g_inode_sem semaphore
*
****************************************************************************/
#ifdef CONFIG_PSEUDOFS_SOFTLINKS
static int _inode_linktarget(FAR struct inode *node,
FAR struct inode_search_s *desc)
{
unsigned int count = 0;
bool save;
int ret = -ENOENT;
DEBUGASSERT(desc != NULL && node != NULL);
/* An infinite loop is avoided only by the loop count. */
save = desc->nofollow;
while (INODE_IS_SOFTLINK(node))
{
FAR const char *link = (FAR const char *)node->u.i_link;
/* Reset and reinitialize the search descriptor. */
RELEASE_SEARCH(desc);
SETUP_SEARCH(desc, link, true);
/* Look up inode associated with the target of the symbolic link */
ret = _inode_search(desc);
if (ret < 0)
{
break;
}
/* Limit the number of symbolic links that we pass through */
if (++count > SYMLOOP_MAX)
{
ret = -ELOOP;
break;
}
/* Set up for the next time through the loop */
node = desc->node;
DEBUGASSERT(node != NULL);
}
desc->nofollow = save;
return ret;
}
#endif
/****************************************************************************
* Name: _inode_search
*
* Description:
* Find the inode associated with 'path' returning the inode references
* and references to its companion nodes. This is the internal, common
* implementation of inode_search().
*
* If a mountpoint is encountered in the search prior to encountering the
* terminal node, the search will terminate at the mountpoint inode. That
* inode and the relative path from the mountpoint, 'relpath' will be
* returned.
*
* If a soft link is encountered that is not the terminal node in the path,
* that link WILL be deferenced unconditionally.
*
* Assumptions:
* The caller holds the g_inode_sem semaphore
*
****************************************************************************/
static int _inode_search(FAR struct inode_search_s *desc)
{
FAR const char *name;
FAR struct inode *node = g_root_inode;
FAR struct inode *left = NULL;
FAR struct inode *above = NULL;
FAR const char *relpath = NULL;
int ret = -ENOENT;
/* Get the search path, skipping over the leading '/'. The leading '/' is
* mandatory because only absolute paths are expected in this context.
*/
DEBUGASSERT(desc != NULL && desc->path != NULL);
name = desc->path;
if (*name != '/')
{
return -EINVAL;
}
/* Traverse the pseudo file system node tree until either (1) all nodes
* have been examined without finding the matching node, or (2) the
* matching node is found.
*/
while (node != NULL)
{
int result = _inode_compare(name, node);
/* Case 1: The name is less than the name of the node.
* Since the names are ordered, these means that there
* is no peer node with this name and that there can be
* no match in the filesystem.
*/
if (result < 0)
{
node = NULL;
break;
}
/* Case 2: the name is greater than the name of the node.
* In this case, the name may still be in the list to the
* "right"
*/
else if (result > 0)
{
/* Continue looking to the "right" of this inode. */
left = node;
node = node->i_peer;
}
/* The names match */
else
{
/* Now there are three remaining possibilities:
* (1) This is the node that we are looking for.
* (2) The node we are looking for is "below" this one.
* (3) This node is a mountpoint and will absorb all requests
* below this one
*/
name = inode_nextname(name);
if (*name == '\0' || INODE_IS_MOUNTPT(node))
{
/* Either (1) we are at the end of the path, so this must be
* the node we are looking for or else (2) this node is a
* mountpoint and will handle the remaining part of the
* pathname
*/
relpath = name;
ret = OK;
break;
}
else
{
/* More nodes to be examined in the path "below" this one. */
#ifdef CONFIG_PSEUDOFS_SOFTLINKS
/* Was the node a soft link? If so, then we need need to
* continue below the target of the link, not the link itself.
*/
if (INODE_IS_SOFTLINK(node))
{
int status;
/* If this intermediate inode in the is a soft link, then
* (1) recursively look-up the inode referenced by the
* soft link, and (2) continue searching with that inode
* instead.
*/
status = _inode_linktarget(node, desc);
if (status < 0)
{
/* Probably means that the target of the symbolic link
* does not exist.
*/
ret = status;
break;
}
else
{
FAR struct inode *newnode = desc->node;
if (newnode != node)
{
/* The node was a valid symbolic link and we have
* jumped to a different, spot in the pseudo file
* system tree.
*/
/* Check if this took us to a mountpoint. */
if (INODE_IS_MOUNTPT(newnode))
{
/* Return the mountpoint information.
* NOTE that the last path to the link target
* was already set by _inode_linktarget().
*/
node = newnode;
above = desc->parent;
left = desc->peer;
ret = OK;
if (*desc->relpath != '\0')
{
char *buffer = NULL;
asprintf(&buffer,
"%s/%s", desc->relpath, name);
if (buffer != NULL)
{
kmm_free(desc->buffer);
desc->buffer = buffer;
relpath = buffer;
}
else
{
ret = -ENOMEM;
}
}
else
{
relpath = name;
}
break;
}
/* Continue from this new inode. */
node = newnode;
}
}
}
#endif
/* Keep looking at the next level "down" */
above = node;
left = NULL;
node = node->i_child;
}
}
}
/* The node may or may not be null as per one of the following four cases
* cases:
*
* With node = NULL
*
* (1) We went left past the final peer: The new node name is larger
* than any existing node name at that level.
* (2) We broke out in the middle of the list of peers because the name
* was not found in the ordered list.
* (3) We went down past the final parent: The new node name is
* "deeper" than anything that we currently have in the tree.
*
* With node != NULL
*
* (4) When the node matching the full path is found
*/
desc->path = name;
desc->node = node;
desc->peer = left;
desc->parent = above;
desc->relpath = relpath;
return ret;
}
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: inode_search
*
* Description:
* Find the inode associated with 'path' returning the inode references
* and references to its companion nodes.
*
* If a mountpoint is encountered in the search prior to encountering the
* terminal node, the search will terminate at the mountpoint inode. That
* inode and the relative path from the mountpoint, 'relpath' will be
* returned.
*
* inode_search will follow soft links in path leading up to the terminal
* node. Whether or no inode_search() will deference that terminal node
* depends on the 'nofollow' input.
*
* If a soft link is encountered that is not the terminal node in the path,
* that link WILL be deferenced unconditionally.
*
* Assumptions:
* The caller holds the g_inode_sem semaphore
*
****************************************************************************/
int inode_search(FAR struct inode_search_s *desc)
{
int ret;
/* Perform the common _inode_search() logic. This does everything except
* operations special operations that must be performed on the terminal
* node if node is a symbolic link.
*/
DEBUGASSERT(desc != NULL);
ret = _inode_search(desc);
#ifdef CONFIG_PSEUDOFS_SOFTLINKS
if (ret >= 0)
{
FAR struct inode *node;
/* Search completed successfully */
node = desc->node;
DEBUGASSERT(node != NULL);
/* Is the terminal node a softlink? Should we follow it? */
if (!desc->nofollow && INODE_IS_SOFTLINK(node))
{
/* The terminating inode is a valid soft link: Return the inode,
* corresponding to link target. _inode_linktarget() will follow
* a link (or a series of links to links) and will return the
* link target of the final symbolic link in the series.
*/
ret = _inode_linktarget(node, desc);
if (ret < 0)
{
/* The most likely cause for failure is that the target of the
* symbolic link does not exist.
*/
return ret;
}
}
}
#endif
return ret;
}
/****************************************************************************
* Name: inode_nextname
*
* Description:
* Given a path with node names separated by '/', return the next path
* segment name.
*
****************************************************************************/
FAR const char *inode_nextname(FAR const char *name)
{
/* Search for the '/' delimiter or the NUL terminator at the end of the
* path segment.
*/
while (*name != '\0' && *name != '/')
{
name++;
}
/* If we found the '/' delimiter, then the path segment we want begins at
* the next character (which might also be the NUL terminator).
*/
while (*name == '/')
{
name++;
}
return name;
}
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