/*
   * Copyright (c) 2006-2007 Silicon Graphics, Inc.

   * Copyright (c) 2014 Christoph Hellwig.

   * All Rights Reserved.
   *
   * 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.
   *
   * This program is distributed in the hope that it would 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 the Free Software Foundation,
   * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
   */
  #include "xfs.h"

  #include "xfs_format.h"

  #include "xfs_log_format.h"
  #include "xfs_trans_resv.h"

  #include "xfs_sb.h"
  #include "xfs_mount.h"

  #include "xfs_defer.h"

  #include "xfs_inode.h"

  #include "xfs_bmap.h"

  #include "xfs_bmap_util.h"

  #include "xfs_alloc.h"

  #include "xfs_mru_cache.h"
  #include "xfs_filestream.h"

  #include "xfs_trace.h"

  #include "xfs_ag_resv.h"

  struct xfs_fstrm_item {
  	struct xfs_mru_cache_elem	mru;
  	struct xfs_inode		*ip;
  	xfs_agnumber_t			ag; /* AG in use for this directory */
  };
  
  enum xfs_fstrm_alloc {
  	XFS_PICK_USERDATA = 1,
  	XFS_PICK_LOWSPACE = 2,
  };

  /*
   * Allocation group filestream associations are tracked with per-ag atomic

   * counters.  These counters allow xfs_filestream_pick_ag() to tell whether a

   * particular AG already has active filestreams associated with it. The mount
   * point's m_peraglock is used to protect these counters from per-ag array
   * re-allocation during a growfs operation.  When xfs_growfs_data_private() is
   * about to reallocate the array, it calls xfs_filestream_flush() with the
   * m_peraglock held in write mode.
   *
   * Since xfs_mru_cache_flush() guarantees that all the free functions for all
   * the cache elements have finished executing before it returns, it's safe for
   * the free functions to use the atomic counters without m_peraglock protection.
   * This allows the implementation of xfs_fstrm_free_func() to be agnostic about
   * whether it was called with the m_peraglock held in read mode, write mode or
   * not held at all.  The race condition this addresses is the following:
   *
   *  - The work queue scheduler fires and pulls a filestream directory cache
   *    element off the LRU end of the cache for deletion, then gets pre-empted.
   *  - A growfs operation grabs the m_peraglock in write mode, flushes all the
   *    remaining items from the cache and reallocates the mount point's per-ag
   *    array, resetting all the counters to zero.
   *  - The work queue thread resumes and calls the free function for the element
   *    it started cleaning up earlier.  In the process it decrements the
   *    filestreams counter for an AG that now has no references.
   *
   * With a shrinkfs feature, the above scenario could panic the system.
   *
   * All other uses of the following macros should be protected by either the
   * m_peraglock held in read mode, or the cache's internal locking exposed by the
   * interval between a call to xfs_mru_cache_lookup() and a call to
   * xfs_mru_cache_done().  In addition, the m_peraglock must be held in read mode
   * when new elements are added to the cache.
   *
   * Combined, these locking rules ensure that no associations will ever exist in
   * the cache that reference per-ag array elements that have since been
   * reallocated.
   */

  int

  xfs_filestream_peek_ag(
  	xfs_mount_t	*mp,
  	xfs_agnumber_t	agno)
  {
  	struct xfs_perag *pag;
  	int		ret;
  
  	pag = xfs_perag_get(mp, agno);
  	ret = atomic_read(&pag->pagf_fstrms);
  	xfs_perag_put(pag);
  	return ret;
  }
  
  static int
  xfs_filestream_get_ag(
  	xfs_mount_t	*mp,
  	xfs_agnumber_t	agno)
  {
  	struct xfs_perag *pag;
  	int		ret;
  
  	pag = xfs_perag_get(mp, agno);
  	ret = atomic_inc_return(&pag->pagf_fstrms);
  	xfs_perag_put(pag);
  	return ret;
  }
  
  static void
  xfs_filestream_put_ag(
  	xfs_mount_t	*mp,
  	xfs_agnumber_t	agno)
  {
  	struct xfs_perag *pag;
  
  	pag = xfs_perag_get(mp, agno);
  	atomic_dec(&pag->pagf_fstrms);
  	xfs_perag_put(pag);
  }

  static void
  xfs_fstrm_free_func(
  	struct xfs_mru_cache_elem *mru)
  {
  	struct xfs_fstrm_item	*item =
  		container_of(mru, struct xfs_fstrm_item, mru);
  
  	xfs_filestream_put_ag(item->ip->i_mount, item->ag);

  	trace_xfs_filestream_free(item->ip, item->ag);

  	kmem_free(item);

  }

  /*
   * Scan the AGs starting at startag looking for an AG that isn't in use and has
   * at least minlen blocks free.
   */
  static int

  xfs_filestream_pick_ag(
  	struct xfs_inode	*ip,
  	xfs_agnumber_t		startag,
  	xfs_agnumber_t		*agp,
  	int			flags,
  	xfs_extlen_t		minlen)

  {

  	struct xfs_mount	*mp = ip->i_mount;
  	struct xfs_fstrm_item	*item;
  	struct xfs_perag	*pag;

  	xfs_extlen_t		longest, free = 0, minfree, maxfree = 0;

  	xfs_agnumber_t		ag, max_ag = NULLAGNUMBER;

  	int			err, trylock, nscan;

  	ASSERT(S_ISDIR(VFS_I(ip)->i_mode));

  
  	/* 2% of an AG's blocks must be free for it to be chosen. */
  	minfree = mp->m_sb.sb_agblocks / 50;
  
  	ag = startag;
  	*agp = NULLAGNUMBER;
  
  	/* For the first pass, don't sleep trying to init the per-AG. */
  	trylock = XFS_ALLOC_FLAG_TRYLOCK;
  
  	for (nscan = 0; 1; nscan++) {

  		trace_xfs_filestream_scan(ip, ag);

  		pag = xfs_perag_get(mp, ag);

  
  		if (!pag->pagf_init) {
  			err = xfs_alloc_pagf_init(mp, NULL, ag, trylock);

  			if (err && !trylock) {
  				xfs_perag_put(pag);

  				return err;

  			}

  		}
  
  		/* Might fail sometimes during the 1st pass with trylock set. */
  		if (!pag->pagf_init)
  			goto next_ag;
  
  		/* Keep track of the AG with the most free blocks. */
  		if (pag->pagf_freeblks > maxfree) {
  			maxfree = pag->pagf_freeblks;
  			max_ag = ag;
  		}
  
  		/*
  		 * The AG reference count does two things: it enforces mutual
  		 * exclusion when examining the suitability of an AG in this
  		 * loop, and it guards against two filestreams being established
  		 * in the same AG as each other.
  		 */
  		if (xfs_filestream_get_ag(mp, ag) > 1) {
  			xfs_filestream_put_ag(mp, ag);
  			goto next_ag;
  		}

  		longest = xfs_alloc_longest_free_extent(mp, pag,

  				xfs_alloc_min_freelist(mp, pag),
  				xfs_ag_resv_needed(pag, XFS_AG_RESV_NONE));

  		if (((minlen && longest >= minlen) ||
  		     (!minlen && pag->pagf_freeblks >= minfree)) &&
  		    (!pag->pagf_metadata || !(flags & XFS_PICK_USERDATA) ||
  		     (flags & XFS_PICK_LOWSPACE))) {
  
  			/* Break out, retaining the reference on the AG. */
  			free = pag->pagf_freeblks;

  			xfs_perag_put(pag);

  			*agp = ag;
  			break;
  		}
  
  		/* Drop the reference on this AG, it's not usable. */
  		xfs_filestream_put_ag(mp, ag);
  next_ag:

  		xfs_perag_put(pag);

  		/* Move to the next AG, wrapping to AG 0 if necessary. */
  		if (++ag >= mp->m_sb.sb_agcount)
  			ag = 0;
  
  		/* If a full pass of the AGs hasn't been done yet, continue. */
  		if (ag != startag)
  			continue;
  
  		/* Allow sleeping in xfs_alloc_pagf_init() on the 2nd pass. */
  		if (trylock != 0) {
  			trylock = 0;
  			continue;
  		}
  
  		/* Finally, if lowspace wasn't set, set it for the 3rd pass. */
  		if (!(flags & XFS_PICK_LOWSPACE)) {
  			flags |= XFS_PICK_LOWSPACE;
  			continue;
  		}
  
  		/*
  		 * Take the AG with the most free space, regardless of whether
  		 * it's already in use by another filestream.
  		 */
  		if (max_ag != NULLAGNUMBER) {
  			xfs_filestream_get_ag(mp, max_ag);

  			free = maxfree;
  			*agp = max_ag;
  			break;
  		}
  
  		/* take AG 0 if none matched */

  		trace_xfs_filestream_pick(ip, *agp, free, nscan);

  		*agp = 0;
  		return 0;
  	}

  	trace_xfs_filestream_pick(ip, *agp, free, nscan);

  	if (*agp == NULLAGNUMBER)

  		return 0;

  	err = -ENOMEM;

  	item = kmem_alloc(sizeof(*item), KM_MAYFAIL);

  	if (!item)

  		goto out_put_ag;

  	item->ag = *agp;

  	item->ip = ip;

  	err = xfs_mru_cache_insert(mp->m_filestream, ip->i_ino, &item->mru);

  	if (err) {

  		if (err == -EEXIST)

  			err = 0;
  		goto out_free_item;

  	}

  	return 0;

  out_free_item:

  	kmem_free(item);

  out_put_ag:
  	xfs_filestream_put_ag(mp, *agp);
  	return err;

  }

  static struct xfs_inode *
  xfs_filestream_get_parent(
  	struct xfs_inode	*ip)

  {

  	struct inode		*inode = VFS_I(ip), *dir = NULL;
  	struct dentry		*dentry, *parent;

  	dentry = d_find_alias(inode);
  	if (!dentry)
  		goto out;

  	parent = dget_parent(dentry);
  	if (!parent)
  		goto out_dput;

  	dir = igrab(d_inode(parent));

  	dput(parent);

  out_dput:
  	dput(dentry);
  out:
  	return dir ? XFS_I(dir) : NULL;

  }
  
  /*

   * Find the right allocation group for a file, either by finding an
   * existing file stream or creating a new one.
   *
   * Returns NULLAGNUMBER in case of an error.

   */
  xfs_agnumber_t
  xfs_filestream_lookup_ag(

  	struct xfs_inode	*ip)

  {

  	struct xfs_mount	*mp = ip->i_mount;

  	struct xfs_inode	*pip = NULL;

  	xfs_agnumber_t		startag, ag = NULLAGNUMBER;

  	struct xfs_mru_cache_elem *mru;

  	ASSERT(S_ISREG(VFS_I(ip)->i_mode));

  	pip = xfs_filestream_get_parent(ip);
  	if (!pip)

  		return NULLAGNUMBER;

  
  	mru = xfs_mru_cache_lookup(mp->m_filestream, pip->i_ino);

  	if (mru) {

  		ag = container_of(mru, struct xfs_fstrm_item, mru)->ag;

  		xfs_mru_cache_done(mp->m_filestream);

  		trace_xfs_filestream_lookup(ip, ag);

  		goto out;

  	}
  
  	/*
  	 * Set the starting AG using the rotor for inode32, otherwise
  	 * use the directory inode's AG.
  	 */
  	if (mp->m_flags & XFS_MOUNT_32BITINODES) {

  		xfs_agnumber_t	 rotorstep = xfs_rotorstep;

  		startag = (mp->m_agfrotor / rotorstep) % mp->m_sb.sb_agcount;
  		mp->m_agfrotor = (mp->m_agfrotor + 1) %
  		                 (mp->m_sb.sb_agcount * rotorstep);
  	} else
  		startag = XFS_INO_TO_AGNO(mp, pip->i_ino);

  	if (xfs_filestream_pick_ag(pip, startag, &ag, 0, 0))
  		ag = NULLAGNUMBER;
  out:
  	IRELE(pip);
  	return ag;

  }
  
  /*

   * Pick a new allocation group for the current file and its file stream.
   *
   * This is called when the allocator can't find a suitable extent in the
   * current AG, and we have to move the stream into a new AG with more space.

   */
  int
  xfs_filestream_new_ag(

  	struct xfs_bmalloca	*ap,
  	xfs_agnumber_t		*agp)

  {

  	struct xfs_inode	*ip = ap->ip, *pip;
  	struct xfs_mount	*mp = ip->i_mount;
  	xfs_extlen_t		minlen = ap->length;
  	xfs_agnumber_t		startag = 0;

  	int			flags = 0;
  	int			err = 0;

  	struct xfs_mru_cache_elem *mru;

  	*agp = NULLAGNUMBER;

  	pip = xfs_filestream_get_parent(ip);
  	if (!pip)
  		goto exit;

  	mru = xfs_mru_cache_remove(mp->m_filestream, pip->i_ino);
  	if (mru) {
  		struct xfs_fstrm_item *item =
  			container_of(mru, struct xfs_fstrm_item, mru);
  		startag = (item->ag + 1) % mp->m_sb.sb_agcount;

  	}

  	if (xfs_alloc_is_userdata(ap->datatype))
  		flags |= XFS_PICK_USERDATA;
  	if (ap->dfops->dop_low)
  		flags |= XFS_PICK_LOWSPACE;

  	err = xfs_filestream_pick_ag(pip, startag, agp, flags, minlen);

  
  	/*

  	 * Only free the item here so we skip over the old AG earlier.

  	 */

  	if (mru)
  		xfs_fstrm_free_func(mru);

  	IRELE(pip);
  exit:
  	if (*agp == NULLAGNUMBER)
  		*agp = 0;
  	return err;
  }

  void
  xfs_filestream_deassociate(
  	struct xfs_inode	*ip)
  {
  	xfs_mru_cache_delete(ip->i_mount->m_filestream, ip->i_ino);
  }

  int
  xfs_filestream_mount(
  	xfs_mount_t	*mp)
  {

  	/*

  	 * The filestream timer tunable is currently fixed within the range of
  	 * one second to four minutes, with five seconds being the default.  The
  	 * group count is somewhat arbitrary, but it'd be nice to adhere to the
  	 * timer tunable to within about 10 percent.  This requires at least 10
  	 * groups.

  	 */

  	return xfs_mru_cache_create(&mp->m_filestream, xfs_fstrm_centisecs * 10,
  				    10, xfs_fstrm_free_func);
  }

  void
  xfs_filestream_unmount(
  	xfs_mount_t	*mp)
  {
  	xfs_mru_cache_destroy(mp->m_filestream);
  }