sos-code-article10/sos/fs_nscache.c

/* Copyright (C) 2005      David Decotigny
   Copyright (C) 2000-2005 The KOS Team (Thomas Petazzoni, David
                           Decotigny, Julien Munier)

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation; either version 2
   of the License, or (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
   USA. 
*/

#include <sos/assert.h>
#include <sos/list.h>
#include <sos/kmem_slab.h>
#include <sos/kmalloc.h>

#include "fs_nscache.h"


/**
 * A so-called "dentry" / "nsnode" structure. Used to make the
 * "in-memory" representation of the file system files/dir/devices
 * that have been used up to now
 */
struct sos_fs_nscache_node
{
  /** The reference to the associated sos_fs_node */
  struct sos_fs_node     *fs_node;

  struct sos_fs_pathname name;

  /** Number of references to that node, reference from parent (if
      any) is EXCLUDED */
  sos_count_t ref_cnt;

  /*
   * Ued to chain the mounted filesystem
   */

  /** If this node is a mountpoint (a file system is mounted on it):
      reference to the filesystem mounted on it */
  struct sos_fs_nscache_node *mounted_root;
  /** If this node is the root of a mounted filesystem: reference to
      the mountpoint where it is mounted on */
  struct sos_fs_nscache_node *mountpoint;

  /** ".." */
  struct sos_fs_nscache_node *parent;

  /** List of the already known children */
  struct sos_fs_nscache_node *children;
  
  /** Other children for the same parent */
  struct sos_fs_nscache_node *siblings_prev, *siblings_next;
};


/** The cache of nscache_node objects */
static struct sos_kslab_cache * cache_of_nscache_nodes;


sos_ret_t sos_fs_nscache_subsystem_setup()
{
  cache_of_nscache_nodes
    = sos_kmem_cache_create("fs_nscache",
			    sizeof(struct sos_fs_nscache_node),
			    3, 0,
			    SOS_KSLAB_CREATE_MAP | SOS_KSLAB_CREATE_ZERO);
  if (! cache_of_nscache_nodes)
    return -SOS_ENOMEM;

  return SOS_OK;
};


sos_bool_t
sos_fs_pathname_eat_slashes(const struct sos_fs_pathname * path,
			    struct sos_fs_pathname * result)
{
  sos_bool_t retval = FALSE;

  result->contents = path->contents;
  result->length   = path->length;
  while (result->length > 0)
    {
      if (*result->contents != '/')
	break;

      result->contents ++;
      result->length --;
      retval = TRUE;
    }

  if(result->length <= 0)
    result->contents = NULL;

  return retval;
}


static sos_bool_t
sos_fs_pathname_eat_non_slashes(const struct sos_fs_pathname * path,
				struct sos_fs_pathname * result)
{
  sos_bool_t retval = FALSE;

  result->contents = path->contents;
  result->length   = path->length;
  while (result->length > 0)
    {
      if (*result->contents == '/')
	break;

      result->contents ++;
      result->length --;
      retval = TRUE;
    }

  if(result->length <= 0)
    result->contents = NULL;

  return retval;
}


sos_bool_t
sos_fs_pathname_split_path(const struct sos_fs_pathname * path,
			   struct sos_fs_pathname * result_first_component,
			   struct sos_fs_pathname * result_remaining_path)
{
  result_first_component->contents = path->contents;
  result_first_component->length   = path->length;

  /* Skip any leading slash */
  sos_fs_pathname_eat_slashes(result_first_component,
			      result_first_component);

  /* Extract the first component */
  sos_fs_pathname_eat_non_slashes(result_first_component,
				  result_remaining_path);
  SOS_ASSERT_FATAL(result_remaining_path->length >= 0);
  result_first_component->length -= result_remaining_path->length;

  /* Return true if there is something left (at least one slash) */
  return (result_remaining_path->length > 0);
}


sos_bool_t fs_pathname_iseq(const struct sos_fs_pathname * p1,
			    const struct sos_fs_pathname * p2)
{
  if (!p1->contents)
    SOS_ASSERT_FATAL(p1->length == 0);
  if (!p2->contents)
    SOS_ASSERT_FATAL(p2->length == 0);

  if (p1->length != p2->length)
    return FALSE;

  if (p1->length == 0)
    return TRUE;

  return (0 == memcmp(p1->contents, p2->contents, p1->length));
}


#define fs_pathname_isstr(str,path) \
  ({ struct sos_fs_pathname _s; _s.contents = str; _s.length = sizeof(str)-1; \
     fs_pathname_iseq(&_s, (path)); })


struct sos_fs_node *
sos_fs_nscache_get_fs_node(const struct sos_fs_nscache_node * nsnode)
{
  return nsnode->fs_node;
}


sos_ret_t
sos_fs_nscache_get_parent(const struct sos_fs_nscache_node * nsnode,
			  struct sos_fs_nscache_node ** result_parent)
{
  *result_parent = nsnode->parent;
  if (*result_parent)
    return SOS_OK;
  return -SOS_ENOENT;
}


sos_ret_t
sos_fs_nscache_get_name(const struct sos_fs_nscache_node * nsnode,
			struct sos_fs_pathname * result_pathname)
{
  result_pathname->contents = nsnode->name.contents;
  result_pathname->length   = nsnode->name.length;
  return SOS_OK;
}


sos_ret_t
sos_fs_nscache_get_ref_cnt(const struct sos_fs_nscache_node * nsnode)
{
  return nsnode->ref_cnt;
}


sos_ret_t
sos_fs_nscache_lookup(struct sos_fs_nscache_node * cur_nsnode,
		      const struct sos_fs_pathname * node_name,
		      const struct sos_fs_nscache_node * root_nsnode,
		      struct sos_fs_nscache_node ** result_nsnode)
{
  if (fs_pathname_isstr(".", node_name))
    {
      *result_nsnode = cur_nsnode;
    }
  else if (fs_pathname_isstr("..", node_name))
    {
      /* Effectively go up only if we did not reach a root node */
      if (cur_nsnode == root_nsnode) /* did reach chroot */
	{
	  /* Simply stay here */
	  *result_nsnode = cur_nsnode;
	}
      else
	{
	  /* If current node is a mounted FS, rewind the mountpoint
	     chain */
	  for ( ; cur_nsnode->mountpoint ; cur_nsnode = cur_nsnode->mountpoint)
	    /* nop */ ;

	  /* Now go up to parent */
	  SOS_ASSERT_FATAL(NULL != cur_nsnode->parent);
	  *result_nsnode = cur_nsnode->parent;
	}

      /* Update the nscache_node result */
      sos_fs_nscache_ref_node(*result_nsnode);
      return SOS_OK;
    }
  else
    {
      /* Normal lookup: we iterate over the list of children nscache
	 nodes */
      int nb_children;
      struct sos_fs_nscache_node * child;

      /* Lookup the child node with the correct name, if any */
      list_foreach_named(cur_nsnode->children,
			 child, nb_children,
			 siblings_prev, siblings_next)
	{
	  struct sos_fs_node * fs_node = cur_nsnode->fs_node;
	  
	  if (fs_node->fs->nsnode_same_name)
	    {
	      if (fs_node->fs->
		    nsnode_same_name(child->name.contents,
				     child->name.length,
				     node_name->contents,
				     node_name->length))
		break;
	    }
	  else
	    if (fs_pathname_iseq(& child->name,
				 node_name))
	      break;
	}

      /* Did not find it ! */
      if (! list_foreach_early_break(cur_nsnode->children,
				     child, nb_children))
	return -SOS_ENOENT;

      /* Yes, found it ! */
      *result_nsnode = child;
    }

  /* Found it. Now, Follow the mountpoint chain, if any */
  for ( ; (*result_nsnode)->mounted_root ;
	*result_nsnode = (*result_nsnode)->mounted_root)
    /* nop */ ;

  /* Update the nscache_node result */
  sos_fs_nscache_ref_node(*result_nsnode);

  return SOS_OK;
}


sos_ret_t sos_fs_nscache_ref_node(struct sos_fs_nscache_node * nsnode)
{
  SOS_ASSERT_FATAL(nsnode->ref_cnt > 0);
  nsnode->ref_cnt ++;
  return SOS_OK;
}


/* Eventually collapses a whole list of nsnodes (non recursive) */
sos_ret_t _sos_fs_nscache_unref_node(struct sos_fs_nscache_node ** nsnode)
{
  struct sos_fs_nscache_node * to_delete = NULL, *node;

  node = *nsnode;
  *nsnode = NULL;

  while (node)
    {
      /* Unreference this node */
      SOS_ASSERT_FATAL(node->ref_cnt > 0);
      node->ref_cnt --;

      /* Is it a good candidate for deletion ? */
      if (node->ref_cnt > 0)
	break; /* No */

      if (node->parent)
	{
	  struct sos_fs_nscache_node * parent = node->parent;

	  SOS_ASSERT_FATAL(node->parent->ref_cnt >= 1);

	  list_delete_named(parent->children, node,
			    siblings_prev, siblings_next);
	  /* The parent lost one child: next iteration will decrement
	     ths parent's ref cnt */
	}

      /* Add to the list of elements to suppress */
      list_add_tail_named(to_delete, node, siblings_prev, siblings_next);

      /* Now look if parent (if any) can be destroyed */
      node = node->parent;
    }

  /* Now destroy all the elements gathered */
  while (! list_is_empty_named(to_delete, siblings_prev, siblings_next))
    {
      node = list_pop_head_named(to_delete, siblings_prev, siblings_next);
      sos_fs_unref_fsnode(node->fs_node);
      sos_kfree((sos_vaddr_t)node);
    }

  return SOS_OK;
}


sos_ret_t
sos_fs_nscache_add_new_child_node(struct sos_fs_nscache_node * parent,
				  const struct sos_fs_pathname * node_name,
				  struct sos_fs_node * fsnode,
				  struct sos_fs_nscache_node ** result_nsnode)
{
  struct sos_fs_nscache_node * nsnode;

  /* Allocate a new nscache node from slab */
  nsnode = (struct sos_fs_nscache_node*)
    sos_kmem_cache_alloc(cache_of_nscache_nodes,
			 SOS_KSLAB_ALLOC_ATOMIC);
  if (! nsnode)
    return -SOS_ENOMEM;

  /* Allocate a new memory chunk to hold the node's name */
  if (node_name && (node_name->length > 0))
    {
      char * contents = (char*) sos_kmalloc(node_name->length,
					    SOS_KMALLOC_ATOMIC);
      if (! contents)
	{
	  sos_kfree((sos_vaddr_t)nsnode);
	  return -SOS_ENOMEM;
	}

      memcpy(contents, node_name->contents, node_name->length);
      nsnode->name.contents = contents;
      nsnode->name.length   = node_name->length;
    }

  /* Now initialize the new node's fields */
  nsnode->ref_cnt = 1;
  sos_fs_ref_fsnode(fsnode);
  nsnode->fs_node = fsnode;

  /* Register this node as a child of its parent, if any */
  nsnode->parent  = parent;
  if (parent)
    {
      sos_fs_nscache_ref_node(parent);
      list_add_head_named(parent->children, nsnode,
			  siblings_prev, siblings_next);
    }

  *result_nsnode = nsnode;
  return SOS_OK;
}


sos_ret_t
sos_fs_nscache_add_existing_child_node(struct sos_fs_nscache_node * parent,
				       const struct sos_fs_pathname * node_name,
				       struct sos_fs_nscache_node * nsnode)
{
  SOS_ASSERT_FATAL(nsnode->parent == NULL);

  /* If the node already had a name, suppress it */
  if (NULL != nsnode->name.contents)
    {
      sos_kfree((sos_vaddr_t)nsnode->name.contents);
    }
  memset(& nsnode->name, 0x0, sizeof(struct sos_fs_pathname));

  /* Allocate a new memory chunk to hold the node's name */
  if (node_name && (node_name->length > 0))
    {
      char * contents = (char*) sos_kmalloc(node_name->length,
					    SOS_KMALLOC_ATOMIC);
      if (! contents)
	{
	  sos_kfree((sos_vaddr_t)nsnode);
	  return -SOS_ENOMEM;
	}

      memcpy(contents, node_name->contents, node_name->length);
      nsnode->name.contents = contents;
      nsnode->name.length   = node_name->length;
    }


  /* Register this node as a child of its parent, if any */
  nsnode->parent  = parent;
  if (parent)
    {
      sos_fs_nscache_ref_node(parent);
      list_add_head_named(parent->children, nsnode,
			  siblings_prev, siblings_next);
    }
  return SOS_OK;
}


sos_ret_t
sos_fs_nscache_disconnect_node(struct sos_fs_nscache_node * nsnode)
{
  if (! nsnode->parent)
    return SOS_OK;

  list_delete_named(nsnode->parent->children, nsnode,
		    siblings_prev, siblings_next);
  sos_fs_nscache_unref_node(nsnode->parent);
  nsnode->parent = NULL;

  return SOS_OK;
}


sos_ret_t
sos_fs_nscache_register_opened_file(struct sos_fs_nscache_node * nsnode,
				    struct sos_fs_opened_file * of)
{
  of->direntry = nsnode;
  sos_fs_nscache_ref_node(nsnode);
  return SOS_OK;
}


sos_ret_t
sos_fs_nscache_mount(struct sos_fs_nscache_node * mountpoint,
		     struct sos_fs_nscache_node * mounted_root)
{
  SOS_ASSERT_FATAL(NULL == mountpoint->mounted_root);
  SOS_ASSERT_FATAL(NULL == mounted_root->mountpoint);
  mountpoint->mounted_root = mounted_root;
  mounted_root->mountpoint = mountpoint;
  sos_fs_nscache_ref_node(mountpoint);
  sos_fs_nscache_ref_node(mounted_root);
  
  return SOS_OK;
}


sos_ret_t
sos_fs_nscache_umount(struct sos_fs_nscache_node * mounted_root)
{
  struct sos_fs_manager_instance *fs;

  SOS_ASSERT_FATAL(NULL != mounted_root->mountpoint);
  SOS_ASSERT_FATAL(mounted_root->mountpoint->mounted_root == mounted_root);

  /* No FS should be mounted on the mounted root to umount */
  SOS_ASSERT_FATAL(NULL == mounted_root->mounted_root);

  /* The mounted root should have its own reference, plus a reference
     from the mountpoint and from the fs instance */
  SOS_ASSERT_FATAL(mounted_root->ref_cnt >= 3);
  if (mounted_root->ref_cnt != 3)
    return -SOS_EBUSY;

  fs = mounted_root->fs_node->fs;
  SOS_ASSERT_FATAL(NULL != fs);
  SOS_ASSERT_FATAL(fs->root == mounted_root);

  /* Undo the mountpoint <-> mounted_root mutual reference */
  mounted_root->mountpoint->mounted_root = NULL;
  sos_fs_nscache_unref_node(mounted_root->mountpoint);
  mounted_root->mountpoint = NULL;
  sos_fs_nscache_unref_node(mounted_root);

  /* Undo the fs->root -> mounted_root reference */
  sos_fs_nscache_unref_node(fs->root);

  return SOS_OK;
}

sos_bool_t
sos_fs_nscache_is_mountnode(const struct sos_fs_nscache_node * nsnode)
{
  return ( (NULL != nsnode->mounted_root) || (NULL != nsnode->mountpoint) );
}