/*
   * V9FS cache definitions.
   *
   *  Copyright (C) 2009 by Abhishek Kulkarni <adkulkar@umail.iu.edu>
   *
   *  This program is free software; you can redistribute it and/or modify
   *  it under the terms of the GNU General Public License version 2
   *  as published by the Free Software Foundation.
   *
   *  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:
   *  Free Software Foundation
   *  51 Franklin Street, Fifth Floor
   *  Boston, MA  02111-1301  USA
   *
   */
  
  #include <linux/jiffies.h>
  #include <linux/file.h>

  #include <linux/slab.h>

  #include <linux/stat.h>
  #include <linux/sched.h>
  #include <linux/fs.h>
  #include <net/9p/9p.h>
  
  #include "v9fs.h"
  #include "cache.h"
  
  #define CACHETAG_LEN  11

  struct fscache_netfs v9fs_cache_netfs = {
  	.name 		= "9p",
  	.version 	= 0,
  };

  /**
   * v9fs_random_cachetag - Generate a random tag to be associated
   *			  with a new cache session.
   *
   * The value of jiffies is used for a fairly randomly cache tag.
   */
  
  static
  int v9fs_random_cachetag(struct v9fs_session_info *v9ses)
  {
  	v9ses->cachetag = kmalloc(CACHETAG_LEN, GFP_KERNEL);
  	if (!v9ses->cachetag)
  		return -ENOMEM;
  
  	return scnprintf(v9ses->cachetag, CACHETAG_LEN, "%lu", jiffies);
  }
  
  static uint16_t v9fs_cache_session_get_key(const void *cookie_netfs_data,
  					   void *buffer, uint16_t bufmax)
  {
  	struct v9fs_session_info *v9ses;
  	uint16_t klen = 0;
  
  	v9ses = (struct v9fs_session_info *)cookie_netfs_data;

  	p9_debug(P9_DEBUG_FSC, "session %p buf %p size %u
  ",
  		 v9ses, buffer, bufmax);

  
  	if (v9ses->cachetag)
  		klen = strlen(v9ses->cachetag);
  
  	if (klen > bufmax)
  		return 0;
  
  	memcpy(buffer, v9ses->cachetag, klen);

  	p9_debug(P9_DEBUG_FSC, "cache session tag %s
  ", v9ses->cachetag);

  	return klen;
  }
  
  const struct fscache_cookie_def v9fs_cache_session_index_def = {

  	.name		= "9P.session",
  	.type		= FSCACHE_COOKIE_TYPE_INDEX,
  	.get_key	= v9fs_cache_session_get_key,

  };
  
  void v9fs_cache_session_get_cookie(struct v9fs_session_info *v9ses)
  {
  	/* If no cache session tag was specified, we generate a random one. */
  	if (!v9ses->cachetag)
  		v9fs_random_cachetag(v9ses);
  
  	v9ses->fscache = fscache_acquire_cookie(v9fs_cache_netfs.primary_index,
  						&v9fs_cache_session_index_def,
  						v9ses);

  	p9_debug(P9_DEBUG_FSC, "session %p get cookie %p
  ",
  		 v9ses, v9ses->fscache);

  }
  
  void v9fs_cache_session_put_cookie(struct v9fs_session_info *v9ses)
  {

  	p9_debug(P9_DEBUG_FSC, "session %p put cookie %p
  ",
  		 v9ses, v9ses->fscache);

  	fscache_relinquish_cookie(v9ses->fscache, 0);
  	v9ses->fscache = NULL;
  }
  
  
  static uint16_t v9fs_cache_inode_get_key(const void *cookie_netfs_data,
  					 void *buffer, uint16_t bufmax)
  {

  	const struct v9fs_inode *v9inode = cookie_netfs_data;

  	memcpy(buffer, &v9inode->qid.path, sizeof(v9inode->qid.path));

  	p9_debug(P9_DEBUG_FSC, "inode %p get key %llu
  ",
  		 &v9inode->vfs_inode, v9inode->qid.path);

  	return sizeof(v9inode->qid.path);

  }
  
  static void v9fs_cache_inode_get_attr(const void *cookie_netfs_data,
  				      uint64_t *size)
  {

  	const struct v9fs_inode *v9inode = cookie_netfs_data;
  	*size = i_size_read(&v9inode->vfs_inode);

  	p9_debug(P9_DEBUG_FSC, "inode %p get attr %llu
  ",
  		 &v9inode->vfs_inode, *size);

  }
  
  static uint16_t v9fs_cache_inode_get_aux(const void *cookie_netfs_data,
  					 void *buffer, uint16_t buflen)
  {

  	const struct v9fs_inode *v9inode = cookie_netfs_data;

  	memcpy(buffer, &v9inode->qid.version, sizeof(v9inode->qid.version));

  	p9_debug(P9_DEBUG_FSC, "inode %p get aux %u
  ",
  		 &v9inode->vfs_inode, v9inode->qid.version);

  	return sizeof(v9inode->qid.version);

  }
  
  static enum
  fscache_checkaux v9fs_cache_inode_check_aux(void *cookie_netfs_data,
  					    const void *buffer,
  					    uint16_t buflen)
  {

  	const struct v9fs_inode *v9inode = cookie_netfs_data;

  	if (buflen != sizeof(v9inode->qid.version))

  		return FSCACHE_CHECKAUX_OBSOLETE;

  	if (memcmp(buffer, &v9inode->qid.version,
  		   sizeof(v9inode->qid.version)))

  		return FSCACHE_CHECKAUX_OBSOLETE;
  
  	return FSCACHE_CHECKAUX_OKAY;
  }
  
  static void v9fs_cache_inode_now_uncached(void *cookie_netfs_data)
  {

  	struct v9fs_inode *v9inode = cookie_netfs_data;

  	struct pagevec pvec;
  	pgoff_t first;
  	int loop, nr_pages;
  
  	pagevec_init(&pvec, 0);
  	first = 0;
  
  	for (;;) {

  		nr_pages = pagevec_lookup(&pvec, v9inode->vfs_inode.i_mapping,

  					  first,
  					  PAGEVEC_SIZE - pagevec_count(&pvec));
  		if (!nr_pages)
  			break;
  
  		for (loop = 0; loop < nr_pages; loop++)
  			ClearPageFsCache(pvec.pages[loop]);
  
  		first = pvec.pages[nr_pages - 1]->index + 1;
  
  		pvec.nr = nr_pages;
  		pagevec_release(&pvec);
  		cond_resched();
  	}
  }
  
  const struct fscache_cookie_def v9fs_cache_inode_index_def = {
  	.name		= "9p.inode",
  	.type		= FSCACHE_COOKIE_TYPE_DATAFILE,
  	.get_key	= v9fs_cache_inode_get_key,
  	.get_attr	= v9fs_cache_inode_get_attr,
  	.get_aux	= v9fs_cache_inode_get_aux,
  	.check_aux	= v9fs_cache_inode_check_aux,
  	.now_uncached	= v9fs_cache_inode_now_uncached,
  };
  
  void v9fs_cache_inode_get_cookie(struct inode *inode)
  {

  	struct v9fs_inode *v9inode;

  	struct v9fs_session_info *v9ses;
  
  	if (!S_ISREG(inode->i_mode))
  		return;

  	v9inode = V9FS_I(inode);
  	if (v9inode->fscache)

  		return;
  
  	v9ses = v9fs_inode2v9ses(inode);

  	v9inode->fscache = fscache_acquire_cookie(v9ses->fscache,

  						  &v9fs_cache_inode_index_def,

  						  v9inode);

  	p9_debug(P9_DEBUG_FSC, "inode %p get cookie %p
  ",
  		 inode, v9inode->fscache);

  }
  
  void v9fs_cache_inode_put_cookie(struct inode *inode)
  {

  	struct v9fs_inode *v9inode = V9FS_I(inode);

  	if (!v9inode->fscache)

  		return;

  	p9_debug(P9_DEBUG_FSC, "inode %p put cookie %p
  ",
  		 inode, v9inode->fscache);

  	fscache_relinquish_cookie(v9inode->fscache, 0);
  	v9inode->fscache = NULL;

  }
  
  void v9fs_cache_inode_flush_cookie(struct inode *inode)
  {

  	struct v9fs_inode *v9inode = V9FS_I(inode);

  	if (!v9inode->fscache)

  		return;

  	p9_debug(P9_DEBUG_FSC, "inode %p flush cookie %p
  ",
  		 inode, v9inode->fscache);

  	fscache_relinquish_cookie(v9inode->fscache, 1);
  	v9inode->fscache = NULL;

  }
  
  void v9fs_cache_inode_set_cookie(struct inode *inode, struct file *filp)
  {

  	struct v9fs_inode *v9inode = V9FS_I(inode);

  	struct p9_fid *fid;

  	if (!v9inode->fscache)

  		return;

  	spin_lock(&v9inode->fscache_lock);

  	fid = filp->private_data;
  	if ((filp->f_flags & O_ACCMODE) != O_RDONLY)
  		v9fs_cache_inode_flush_cookie(inode);
  	else
  		v9fs_cache_inode_get_cookie(inode);

  	spin_unlock(&v9inode->fscache_lock);

  }
  
  void v9fs_cache_inode_reset_cookie(struct inode *inode)
  {

  	struct v9fs_inode *v9inode = V9FS_I(inode);

  	struct v9fs_session_info *v9ses;
  	struct fscache_cookie *old;

  	if (!v9inode->fscache)

  		return;

  	old = v9inode->fscache;

  	spin_lock(&v9inode->fscache_lock);
  	fscache_relinquish_cookie(v9inode->fscache, 1);

  
  	v9ses = v9fs_inode2v9ses(inode);

  	v9inode->fscache = fscache_acquire_cookie(v9ses->fscache,

  						  &v9fs_cache_inode_index_def,

  						  v9inode);

  	p9_debug(P9_DEBUG_FSC, "inode %p revalidating cookie old %p new %p
  ",
  		 inode, old, v9inode->fscache);

  	spin_unlock(&v9inode->fscache_lock);

  }
  
  int __v9fs_fscache_release_page(struct page *page, gfp_t gfp)
  {
  	struct inode *inode = page->mapping->host;

  	struct v9fs_inode *v9inode = V9FS_I(inode);

  	BUG_ON(!v9inode->fscache);

  	return fscache_maybe_release_page(v9inode->fscache, page, gfp);

  }
  
  void __v9fs_fscache_invalidate_page(struct page *page)
  {
  	struct inode *inode = page->mapping->host;

  	struct v9fs_inode *v9inode = V9FS_I(inode);

  	BUG_ON(!v9inode->fscache);

  
  	if (PageFsCache(page)) {

  		fscache_wait_on_page_write(v9inode->fscache, page);

  		BUG_ON(!PageLocked(page));

  		fscache_uncache_page(v9inode->fscache, page);

  	}
  }
  
  static void v9fs_vfs_readpage_complete(struct page *page, void *data,
  				       int error)
  {
  	if (!error)
  		SetPageUptodate(page);
  
  	unlock_page(page);
  }
  
  /**
   * __v9fs_readpage_from_fscache - read a page from cache
   *
   * Returns 0 if the pages are in cache and a BIO is submitted,
   * 1 if the pages are not in cache and -error otherwise.
   */
  
  int __v9fs_readpage_from_fscache(struct inode *inode, struct page *page)
  {
  	int ret;

  	const struct v9fs_inode *v9inode = V9FS_I(inode);

  	p9_debug(P9_DEBUG_FSC, "inode %p page %p
  ", inode, page);

  	if (!v9inode->fscache)

  		return -ENOBUFS;

  	ret = fscache_read_or_alloc_page(v9inode->fscache,

  					 page,
  					 v9fs_vfs_readpage_complete,
  					 NULL,
  					 GFP_KERNEL);
  	switch (ret) {
  	case -ENOBUFS:
  	case -ENODATA:

  		p9_debug(P9_DEBUG_FSC, "page/inode not in cache %d
  ", ret);

  		return 1;
  	case 0:

  		p9_debug(P9_DEBUG_FSC, "BIO submitted
  ");

  		return ret;
  	default:

  		p9_debug(P9_DEBUG_FSC, "ret %d
  ", ret);

  		return ret;
  	}
  }
  
  /**
   * __v9fs_readpages_from_fscache - read multiple pages from cache
   *
   * Returns 0 if the pages are in cache and a BIO is submitted,
   * 1 if the pages are not in cache and -error otherwise.
   */
  
  int __v9fs_readpages_from_fscache(struct inode *inode,
  				  struct address_space *mapping,
  				  struct list_head *pages,
  				  unsigned *nr_pages)
  {
  	int ret;

  	const struct v9fs_inode *v9inode = V9FS_I(inode);

  	p9_debug(P9_DEBUG_FSC, "inode %p pages %u
  ", inode, *nr_pages);

  	if (!v9inode->fscache)

  		return -ENOBUFS;

  	ret = fscache_read_or_alloc_pages(v9inode->fscache,

  					  mapping, pages, nr_pages,
  					  v9fs_vfs_readpage_complete,
  					  NULL,
  					  mapping_gfp_mask(mapping));
  	switch (ret) {
  	case -ENOBUFS:
  	case -ENODATA:

  		p9_debug(P9_DEBUG_FSC, "pages/inodes not in cache %d
  ", ret);

  		return 1;
  	case 0:
  		BUG_ON(!list_empty(pages));
  		BUG_ON(*nr_pages != 0);

  		p9_debug(P9_DEBUG_FSC, "BIO submitted
  ");

  		return ret;
  	default:

  		p9_debug(P9_DEBUG_FSC, "ret %d
  ", ret);

  		return ret;
  	}
  }
  
  /**
   * __v9fs_readpage_to_fscache - write a page to the cache
   *
   */
  
  void __v9fs_readpage_to_fscache(struct inode *inode, struct page *page)
  {
  	int ret;

  	const struct v9fs_inode *v9inode = V9FS_I(inode);

  	p9_debug(P9_DEBUG_FSC, "inode %p page %p
  ", inode, page);

  	ret = fscache_write_page(v9inode->fscache, page, GFP_KERNEL);

  	p9_debug(P9_DEBUG_FSC, "ret =  %d
  ", ret);

  	if (ret != 0)
  		v9fs_uncache_page(inode, page);
  }

  
  /*
   * wait for a page to complete writing to the cache
   */
  void __v9fs_fscache_wait_on_page_write(struct inode *inode, struct page *page)
  {

  	const struct v9fs_inode *v9inode = V9FS_I(inode);

  	p9_debug(P9_DEBUG_FSC, "inode %p page %p
  ", inode, page);

  	if (PageFsCache(page))

  		fscache_wait_on_page_write(v9inode->fscache, page);

  }