#include <linux/ceph/ceph_debug.h>

  
  #include <linux/backing-dev.h>
  #include <linux/fs.h>
  #include <linux/mm.h>
  #include <linux/pagemap.h>
  #include <linux/writeback.h>	/* generic_writepages */

  #include <linux/slab.h>

  #include <linux/pagevec.h>
  #include <linux/task_io_accounting_ops.h>
  
  #include "super.h"

  #include "mds_client.h"
  #include <linux/ceph/osd_client.h>

  
  /*
   * Ceph address space ops.
   *
   * There are a few funny things going on here.
   *
   * The page->private field is used to reference a struct
   * ceph_snap_context for _every_ dirty page.  This indicates which
   * snapshot the page was logically dirtied in, and thus which snap
   * context needs to be associated with the osd write during writeback.
   *
   * Similarly, struct ceph_inode_info maintains a set of counters to
   * count dirty pages on the inode.  In the absense of snapshots,
   * i_wrbuffer_ref == i_wrbuffer_ref_head == the dirty page count.
   *
   * When a snapshot is taken (that is, when the client receives
   * notification that a snapshot was taken), each inode with caps and
   * with dirty pages (dirty pages implies there is a cap) gets a new
   * ceph_cap_snap in the i_cap_snaps list (which is sorted in ascending
   * order, new snaps go to the tail).  The i_wrbuffer_ref_head count is
   * moved to capsnap->dirty. (Unless a sync write is currently in
   * progress.  In that case, the capsnap is said to be "pending", new
   * writes cannot start, and the capsnap isn't "finalized" until the
   * write completes (or fails) and a final size/mtime for the inode for
   * that snap can be settled upon.)  i_wrbuffer_ref_head is reset to 0.
   *
   * On writeback, we must submit writes to the osd IN SNAP ORDER.  So,
   * we look for the first capsnap in i_cap_snaps and write out pages in
   * that snap context _only_.  Then we move on to the next capsnap,
   * eventually reaching the "live" or "head" context (i.e., pages that
   * are not yet snapped) and are writing the most recently dirtied
   * pages.
   *
   * Invalidate and so forth must take care to ensure the dirty page
   * accounting is preserved.
   */

  #define CONGESTION_ON_THRESH(congestion_kb) (congestion_kb >> (PAGE_SHIFT-10))
  #define CONGESTION_OFF_THRESH(congestion_kb)				\
  	(CONGESTION_ON_THRESH(congestion_kb) -				\
  	 (CONGESTION_ON_THRESH(congestion_kb) >> 2))

  
  /*
   * Dirty a page.  Optimistically adjust accounting, on the assumption
   * that we won't race with invalidate.  If we do, readjust.
   */
  static int ceph_set_page_dirty(struct page *page)
  {
  	struct address_space *mapping = page->mapping;
  	struct inode *inode;
  	struct ceph_inode_info *ci;
  	int undo = 0;
  	struct ceph_snap_context *snapc;
  
  	if (unlikely(!mapping))
  		return !TestSetPageDirty(page);
  
  	if (TestSetPageDirty(page)) {
  		dout("%p set_page_dirty %p idx %lu -- already dirty
  ",
  		     mapping->host, page, page->index);
  		return 0;
  	}
  
  	inode = mapping->host;
  	ci = ceph_inode(inode);
  
  	/*
  	 * Note that we're grabbing a snapc ref here without holding
  	 * any locks!
  	 */
  	snapc = ceph_get_snap_context(ci->i_snap_realm->cached_context);
  
  	/* dirty the head */
  	spin_lock(&inode->i_lock);

  	if (ci->i_head_snapc == NULL)

  		ci->i_head_snapc = ceph_get_snap_context(snapc);
  	++ci->i_wrbuffer_ref_head;
  	if (ci->i_wrbuffer_ref == 0)

  		ihold(inode);

  	++ci->i_wrbuffer_ref;
  	dout("%p set_page_dirty %p idx %lu head %d/%d -> %d/%d "
  	     "snapc %p seq %lld (%d snaps)
  ",
  	     mapping->host, page, page->index,
  	     ci->i_wrbuffer_ref-1, ci->i_wrbuffer_ref_head-1,
  	     ci->i_wrbuffer_ref, ci->i_wrbuffer_ref_head,
  	     snapc, snapc->seq, snapc->num_snaps);
  	spin_unlock(&inode->i_lock);
  
  	/* now adjust page */
  	spin_lock_irq(&mapping->tree_lock);
  	if (page->mapping) {	/* Race with truncate? */
  		WARN_ON_ONCE(!PageUptodate(page));

  		account_page_dirtied(page, page->mapping);

  		radix_tree_tag_set(&mapping->page_tree,
  				page_index(page), PAGECACHE_TAG_DIRTY);
  
  		/*
  		 * Reference snap context in page->private.  Also set
  		 * PagePrivate so that we get invalidatepage callback.
  		 */
  		page->private = (unsigned long)snapc;
  		SetPagePrivate(page);
  	} else {
  		dout("ANON set_page_dirty %p (raced truncate?)
  ", page);
  		undo = 1;
  	}
  
  	spin_unlock_irq(&mapping->tree_lock);
  
  	if (undo)
  		/* whoops, we failed to dirty the page */
  		ceph_put_wrbuffer_cap_refs(ci, 1, snapc);
  
  	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
  
  	BUG_ON(!PageDirty(page));
  	return 1;
  }
  
  /*
   * If we are truncating the full page (i.e. offset == 0), adjust the
   * dirty page counters appropriately.  Only called if there is private
   * data on the page.
   */
  static void ceph_invalidatepage(struct page *page, unsigned long offset)
  {

  	struct inode *inode;

  	struct ceph_inode_info *ci;
  	struct ceph_snap_context *snapc = (void *)page->private;
  
  	BUG_ON(!PageLocked(page));
  	BUG_ON(!page->private);
  	BUG_ON(!PagePrivate(page));
  	BUG_ON(!page->mapping);

  	inode = page->mapping->host;

  	/*
  	 * We can get non-dirty pages here due to races between
  	 * set_page_dirty and truncate_complete_page; just spit out a
  	 * warning, in case we end up with accounting problems later.
  	 */
  	if (!PageDirty(page))
  		pr_err("%p invalidatepage %p page not dirty
  ", inode, page);
  
  	if (offset == 0)
  		ClearPageChecked(page);
  
  	ci = ceph_inode(inode);
  	if (offset == 0) {
  		dout("%p invalidatepage %p idx %lu full dirty page %lu
  ",
  		     inode, page, page->index, offset);
  		ceph_put_wrbuffer_cap_refs(ci, 1, snapc);
  		ceph_put_snap_context(snapc);
  		page->private = 0;
  		ClearPagePrivate(page);
  	} else {
  		dout("%p invalidatepage %p idx %lu partial dirty page
  ",
  		     inode, page, page->index);
  	}
  }
  
  /* just a sanity check */
  static int ceph_releasepage(struct page *page, gfp_t g)
  {
  	struct inode *inode = page->mapping ? page->mapping->host : NULL;
  	dout("%p releasepage %p idx %lu
  ", inode, page, page->index);
  	WARN_ON(PageDirty(page));
  	WARN_ON(page->private);
  	WARN_ON(PagePrivate(page));
  	return 0;
  }
  
  /*
   * read a single page, without unlocking it.
   */
  static int readpage_nounlock(struct file *filp, struct page *page)
  {
  	struct inode *inode = filp->f_dentry->d_inode;
  	struct ceph_inode_info *ci = ceph_inode(inode);

  	struct ceph_osd_client *osdc = 
  		&ceph_inode_to_client(inode)->client->osdc;

  	int err = 0;
  	u64 len = PAGE_CACHE_SIZE;
  
  	dout("readpage inode %p file %p page %p index %lu
  ",
  	     inode, filp, page, page->index);
  	err = ceph_osdc_readpages(osdc, ceph_vino(inode), &ci->i_layout,
  				  page->index << PAGE_CACHE_SHIFT, &len,
  				  ci->i_truncate_seq, ci->i_truncate_size,

  				  &page, 1, 0);

  	if (err == -ENOENT)
  		err = 0;
  	if (err < 0) {
  		SetPageError(page);
  		goto out;
  	} else if (err < PAGE_CACHE_SIZE) {
  		/* zero fill remainder of page */
  		zero_user_segment(page, err, PAGE_CACHE_SIZE);
  	}
  	SetPageUptodate(page);
  
  out:
  	return err < 0 ? err : 0;
  }
  
  static int ceph_readpage(struct file *filp, struct page *page)
  {
  	int r = readpage_nounlock(filp, page);
  	unlock_page(page);
  	return r;
  }
  
  /*
   * Build a vector of contiguous pages from the provided page list.
   */
  static struct page **page_vector_from_list(struct list_head *page_list,
  					   unsigned *nr_pages)
  {
  	struct page **pages;
  	struct page *page;
  	int next_index, contig_pages = 0;
  
  	/* build page vector */
  	pages = kmalloc(sizeof(*pages) * *nr_pages, GFP_NOFS);
  	if (!pages)
  		return ERR_PTR(-ENOMEM);
  
  	BUG_ON(list_empty(page_list));
  	next_index = list_entry(page_list->prev, struct page, lru)->index;
  	list_for_each_entry_reverse(page, page_list, lru) {
  		if (page->index == next_index) {
  			dout("readpages page %d %p
  ", contig_pages, page);
  			pages[contig_pages] = page;
  			contig_pages++;
  			next_index++;
  		} else {
  			break;
  		}
  	}
  	*nr_pages = contig_pages;
  	return pages;
  }
  
  /*
   * Read multiple pages.  Leave pages we don't read + unlock in page_list;
   * the caller (VM) cleans them up.
   */
  static int ceph_readpages(struct file *file, struct address_space *mapping,
  			  struct list_head *page_list, unsigned nr_pages)
  {
  	struct inode *inode = file->f_dentry->d_inode;
  	struct ceph_inode_info *ci = ceph_inode(inode);

  	struct ceph_osd_client *osdc =
  		&ceph_inode_to_client(inode)->client->osdc;

  	int rc = 0;
  	struct page **pages;

  	loff_t offset;
  	u64 len;
  
  	dout("readpages %p file %p nr_pages %d
  ",
  	     inode, file, nr_pages);
  
  	pages = page_vector_from_list(page_list, &nr_pages);
  	if (IS_ERR(pages))
  		return PTR_ERR(pages);
  
  	/* guess read extent */
  	offset = pages[0]->index << PAGE_CACHE_SHIFT;
  	len = nr_pages << PAGE_CACHE_SHIFT;
  	rc = ceph_osdc_readpages(osdc, ceph_vino(inode), &ci->i_layout,
  				 offset, &len,
  				 ci->i_truncate_seq, ci->i_truncate_size,

  				 pages, nr_pages, 0);

  	if (rc == -ENOENT)
  		rc = 0;
  	if (rc < 0)
  		goto out;

  	for (; !list_empty(page_list) && len > 0;
  	     rc -= PAGE_CACHE_SIZE, len -= PAGE_CACHE_SIZE) {
  		struct page *page =
  			list_entry(page_list->prev, struct page, lru);
  
  		list_del(&page->lru);
  
  		if (rc < (int)PAGE_CACHE_SIZE) {
  			/* zero (remainder of) page */
  			int s = rc < 0 ? 0 : rc;
  			zero_user_segment(page, s, PAGE_CACHE_SIZE);
  		}

  		if (add_to_page_cache_lru(page, mapping, page->index,
  					  GFP_NOFS)) {

  			page_cache_release(page);
  			dout("readpages %p add_to_page_cache failed %p
  ",
  			     inode, page);
  			continue;
  		}
  		dout("readpages %p adding %p idx %lu
  ", inode, page,
  		     page->index);
  		flush_dcache_page(page);
  		SetPageUptodate(page);
  		unlock_page(page);

  		page_cache_release(page);

  	}

  	rc = 0;
  
  out:
  	kfree(pages);
  	return rc;
  }
  
  /*
   * Get ref for the oldest snapc for an inode with dirty data... that is, the
   * only snap context we are allowed to write back.

   */

  static struct ceph_snap_context *get_oldest_context(struct inode *inode,
  						    u64 *snap_size)

  {
  	struct ceph_inode_info *ci = ceph_inode(inode);
  	struct ceph_snap_context *snapc = NULL;
  	struct ceph_cap_snap *capsnap = NULL;

  	spin_lock(&inode->i_lock);

  	list_for_each_entry(capsnap, &ci->i_cap_snaps, ci_item) {
  		dout(" cap_snap %p snapc %p has %d dirty pages
  ", capsnap,
  		     capsnap->context, capsnap->dirty_pages);
  		if (capsnap->dirty_pages) {
  			snapc = ceph_get_snap_context(capsnap->context);
  			if (snap_size)
  				*snap_size = capsnap->size;
  			break;
  		}
  	}

  	if (!snapc && ci->i_wrbuffer_ref_head) {

  		snapc = ceph_get_snap_context(ci->i_head_snapc);

  		dout(" head snapc %p has %d dirty pages
  ",
  		     snapc, ci->i_wrbuffer_ref_head);
  	}

  	spin_unlock(&inode->i_lock);
  	return snapc;
  }
  
  /*
   * Write a single page, but leave the page locked.
   *
   * If we get a write error, set the page error bit, but still adjust the
   * dirty page accounting (i.e., page is no longer dirty).
   */
  static int writepage_nounlock(struct page *page, struct writeback_control *wbc)
  {
  	struct inode *inode;
  	struct ceph_inode_info *ci;

  	struct ceph_fs_client *fsc;

  	struct ceph_osd_client *osdc;
  	loff_t page_off = page->index << PAGE_CACHE_SHIFT;
  	int len = PAGE_CACHE_SIZE;
  	loff_t i_size;
  	int err = 0;

  	struct ceph_snap_context *snapc, *oldest;

  	u64 snap_size = 0;

  	long writeback_stat;

  
  	dout("writepage %p idx %lu
  ", page, page->index);
  
  	if (!page->mapping || !page->mapping->host) {
  		dout("writepage %p - no mapping
  ", page);
  		return -EFAULT;
  	}
  	inode = page->mapping->host;
  	ci = ceph_inode(inode);

  	fsc = ceph_inode_to_client(inode);
  	osdc = &fsc->client->osdc;

  
  	/* verify this is a writeable snap context */
  	snapc = (void *)page->private;
  	if (snapc == NULL) {
  		dout("writepage %p page %p not dirty?
  ", inode, page);
  		goto out;
  	}

  	oldest = get_oldest_context(inode, &snap_size);
  	if (snapc->seq > oldest->seq) {

  		dout("writepage %p page %p snapc %p not writeable - noop
  ",
  		     inode, page, (void *)page->private);
  		/* we should only noop if called by kswapd */
  		WARN_ON((current->flags & PF_MEMALLOC) == 0);

  		ceph_put_snap_context(oldest);

  		goto out;
  	}

  	ceph_put_snap_context(oldest);

  
  	/* is this a partial page at end of file? */
  	if (snap_size)
  		i_size = snap_size;
  	else
  		i_size = i_size_read(inode);
  	if (i_size < page_off + len)
  		len = i_size - page_off;

  	dout("writepage %p page %p index %lu on %llu~%u snapc %p
  ",
  	     inode, page, page->index, page_off, len, snapc);

  	writeback_stat = atomic_long_inc_return(&fsc->writeback_count);

  	if (writeback_stat >

  	    CONGESTION_ON_THRESH(fsc->mount_options->congestion_kb))
  		set_bdi_congested(&fsc->backing_dev_info, BLK_RW_ASYNC);

  	set_page_writeback(page);
  	err = ceph_osdc_writepages(osdc, ceph_vino(inode),
  				   &ci->i_layout, snapc,
  				   page_off, len,
  				   ci->i_truncate_seq, ci->i_truncate_size,
  				   &inode->i_mtime,
  				   &page, 1, 0, 0, true);
  	if (err < 0) {
  		dout("writepage setting page/mapping error %d %p
  ", err, page);
  		SetPageError(page);
  		mapping_set_error(&inode->i_data, err);
  		if (wbc)
  			wbc->pages_skipped++;
  	} else {
  		dout("writepage cleaned page %p
  ", page);
  		err = 0;  /* vfs expects us to return 0 */
  	}
  	page->private = 0;
  	ClearPagePrivate(page);
  	end_page_writeback(page);
  	ceph_put_wrbuffer_cap_refs(ci, 1, snapc);

  	ceph_put_snap_context(snapc);  /* page's reference */

  out:
  	return err;
  }
  
  static int ceph_writepage(struct page *page, struct writeback_control *wbc)
  {

  	int err;
  	struct inode *inode = page->mapping->host;
  	BUG_ON(!inode);
  	igrab(inode);
  	err = writepage_nounlock(page, wbc);

  	unlock_page(page);

  	iput(inode);

  	return err;
  }
  
  
  /*
   * lame release_pages helper.  release_pages() isn't exported to
   * modules.
   */
  static void ceph_release_pages(struct page **pages, int num)
  {
  	struct pagevec pvec;
  	int i;
  
  	pagevec_init(&pvec, 0);
  	for (i = 0; i < num; i++) {
  		if (pagevec_add(&pvec, pages[i]) == 0)
  			pagevec_release(&pvec);
  	}
  	pagevec_release(&pvec);
  }
  
  
  /*
   * async writeback completion handler.
   *
   * If we get an error, set the mapping error bit, but not the individual
   * page error bits.
   */
  static void writepages_finish(struct ceph_osd_request *req,
  			      struct ceph_msg *msg)
  {
  	struct inode *inode = req->r_inode;
  	struct ceph_osd_reply_head *replyhead;
  	struct ceph_osd_op *op;
  	struct ceph_inode_info *ci = ceph_inode(inode);
  	unsigned wrote;

  	struct page *page;
  	int i;
  	struct ceph_snap_context *snapc = req->r_snapc;
  	struct address_space *mapping = inode->i_mapping;

  	__s32 rc = -EIO;
  	u64 bytes = 0;

  	struct ceph_fs_client *fsc = ceph_inode_to_client(inode);

  	long writeback_stat;

  	unsigned issued = ceph_caps_issued(ci);

  
  	/* parse reply */
  	replyhead = msg->front.iov_base;
  	WARN_ON(le32_to_cpu(replyhead->num_ops) == 0);
  	op = (void *)(replyhead + 1);
  	rc = le32_to_cpu(replyhead->result);
  	bytes = le64_to_cpu(op->extent.length);
  
  	if (rc >= 0) {

  		/*
  		 * Assume we wrote the pages we originally sent.  The
  		 * osd might reply with fewer pages if our writeback
  		 * raced with a truncation and was adjusted at the osd,
  		 * so don't believe the reply.
  		 */
  		wrote = req->r_num_pages;

  	} else {
  		wrote = 0;
  		mapping_set_error(mapping, rc);
  	}
  	dout("writepages_finish %p rc %d bytes %llu wrote %d (pages)
  ",
  	     inode, rc, bytes, wrote);
  
  	/* clean all pages */
  	for (i = 0; i < req->r_num_pages; i++) {
  		page = req->r_pages[i];
  		BUG_ON(!page);
  		WARN_ON(!PageUptodate(page));

  		writeback_stat =

  			atomic_long_dec_return(&fsc->writeback_count);

  		if (writeback_stat <

  		    CONGESTION_OFF_THRESH(fsc->mount_options->congestion_kb))
  			clear_bdi_congested(&fsc->backing_dev_info,

  					    BLK_RW_ASYNC);

  		ceph_put_snap_context((void *)page->private);

  		page->private = 0;
  		ClearPagePrivate(page);

  		dout("unlocking %d %p
  ", i, page);
  		end_page_writeback(page);

  
  		/*
  		 * We lost the cache cap, need to truncate the page before
  		 * it is unlocked, otherwise we'd truncate it later in the
  		 * page truncation thread, possibly losing some data that
  		 * raced its way in
  		 */

  		if ((issued & (CEPH_CAP_FILE_CACHE|CEPH_CAP_FILE_LAZYIO)) == 0)

  			generic_error_remove_page(inode->i_mapping, page);

  		unlock_page(page);
  	}
  	dout("%p wrote+cleaned %d pages
  ", inode, wrote);
  	ceph_put_wrbuffer_cap_refs(ci, req->r_num_pages, snapc);
  
  	ceph_release_pages(req->r_pages, req->r_num_pages);
  	if (req->r_pages_from_pool)
  		mempool_free(req->r_pages,

  			     ceph_sb_to_client(inode->i_sb)->wb_pagevec_pool);

  	else
  		kfree(req->r_pages);
  	ceph_osdc_put_request(req);
  }
  
  /*
   * allocate a page vec, either directly, or if necessary, via a the
   * mempool.  we avoid the mempool if we can because req->r_num_pages
   * may be less than the maximum write size.
   */

  static void alloc_page_vec(struct ceph_fs_client *fsc,

  			   struct ceph_osd_request *req)
  {
  	req->r_pages = kmalloc(sizeof(struct page *) * req->r_num_pages,
  			       GFP_NOFS);
  	if (!req->r_pages) {

  		req->r_pages = mempool_alloc(fsc->wb_pagevec_pool, GFP_NOFS);

  		req->r_pages_from_pool = 1;
  		WARN_ON(!req->r_pages);
  	}
  }
  
  /*
   * initiate async writeback
   */
  static int ceph_writepages_start(struct address_space *mapping,
  				 struct writeback_control *wbc)
  {
  	struct inode *inode = mapping->host;

  	struct ceph_inode_info *ci = ceph_inode(inode);

  	struct ceph_fs_client *fsc;

  	pgoff_t index, start, end;
  	int range_whole = 0;
  	int should_loop = 1;
  	pgoff_t max_pages = 0, max_pages_ever = 0;

  	struct ceph_snap_context *snapc = NULL, *last_snapc = NULL, *pgsnapc;

  	struct pagevec pvec;
  	int done = 0;
  	int rc = 0;
  	unsigned wsize = 1 << inode->i_blkbits;
  	struct ceph_osd_request *req = NULL;
  	int do_sync;
  	u64 snap_size = 0;
  
  	/*
  	 * Include a 'sync' in the OSD request if this is a data
  	 * integrity write (e.g., O_SYNC write or fsync()), or if our
  	 * cap is being revoked.
  	 */
  	do_sync = wbc->sync_mode == WB_SYNC_ALL;
  	if (ceph_caps_revoking(ci, CEPH_CAP_FILE_BUFFER))
  		do_sync = 1;
  	dout("writepages_start %p dosync=%d (mode=%s)
  ",
  	     inode, do_sync,
  	     wbc->sync_mode == WB_SYNC_NONE ? "NONE" :
  	     (wbc->sync_mode == WB_SYNC_ALL ? "ALL" : "HOLD"));

  	fsc = ceph_inode_to_client(inode);
  	if (fsc->mount_state == CEPH_MOUNT_SHUTDOWN) {

  		pr_warning("writepage_start %p on forced umount
  ", inode);
  		return -EIO; /* we're in a forced umount, don't write! */
  	}

  	if (fsc->mount_options->wsize && fsc->mount_options->wsize < wsize)
  		wsize = fsc->mount_options->wsize;

  	if (wsize < PAGE_CACHE_SIZE)
  		wsize = PAGE_CACHE_SIZE;
  	max_pages_ever = wsize >> PAGE_CACHE_SHIFT;
  
  	pagevec_init(&pvec, 0);

  	/* where to start/end? */
  	if (wbc->range_cyclic) {
  		start = mapping->writeback_index; /* Start from prev offset */
  		end = -1;
  		dout(" cyclic, start at %lu
  ", start);
  	} else {
  		start = wbc->range_start >> PAGE_CACHE_SHIFT;
  		end = wbc->range_end >> PAGE_CACHE_SHIFT;
  		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
  			range_whole = 1;
  		should_loop = 0;
  		dout(" not cyclic, %lu to %lu
  ", start, end);
  	}
  	index = start;
  
  retry:
  	/* find oldest snap context with dirty data */
  	ceph_put_snap_context(snapc);
  	snapc = get_oldest_context(inode, &snap_size);
  	if (!snapc) {
  		/* hmm, why does writepages get called when there
  		   is no dirty data? */
  		dout(" no snap context with dirty data?
  ");
  		goto out;
  	}
  	dout(" oldest snapc is %p seq %lld (%d snaps)
  ",
  	     snapc, snapc->seq, snapc->num_snaps);
  	if (last_snapc && snapc != last_snapc) {
  		/* if we switched to a newer snapc, restart our scan at the
  		 * start of the original file range. */
  		dout("  snapc differs from last pass, restarting at %lu
  ",
  		     index);
  		index = start;
  	}
  	last_snapc = snapc;
  
  	while (!done && index <= end) {
  		unsigned i;
  		int first;
  		pgoff_t next;
  		int pvec_pages, locked_pages;
  		struct page *page;
  		int want;
  		u64 offset, len;
  		struct ceph_osd_request_head *reqhead;
  		struct ceph_osd_op *op;

  		long writeback_stat;

  
  		next = 0;
  		locked_pages = 0;
  		max_pages = max_pages_ever;
  
  get_more_pages:
  		first = -1;
  		want = min(end - index,
  			   min((pgoff_t)PAGEVEC_SIZE,
  			       max_pages - (pgoff_t)locked_pages) - 1)
  			+ 1;
  		pvec_pages = pagevec_lookup_tag(&pvec, mapping, &index,
  						PAGECACHE_TAG_DIRTY,
  						want);
  		dout("pagevec_lookup_tag got %d
  ", pvec_pages);
  		if (!pvec_pages && !locked_pages)
  			break;
  		for (i = 0; i < pvec_pages && locked_pages < max_pages; i++) {
  			page = pvec.pages[i];
  			dout("? %p idx %lu
  ", page, page->index);
  			if (locked_pages == 0)
  				lock_page(page);  /* first page */
  			else if (!trylock_page(page))
  				break;
  
  			/* only dirty pages, or our accounting breaks */
  			if (unlikely(!PageDirty(page)) ||
  			    unlikely(page->mapping != mapping)) {
  				dout("!dirty or !mapping %p
  ", page);
  				unlock_page(page);
  				break;
  			}
  			if (!wbc->range_cyclic && page->index > end) {
  				dout("end of range %p
  ", page);
  				done = 1;
  				unlock_page(page);
  				break;
  			}
  			if (next && (page->index != next)) {
  				dout("not consecutive %p
  ", page);
  				unlock_page(page);
  				break;
  			}
  			if (wbc->sync_mode != WB_SYNC_NONE) {
  				dout("waiting on writeback %p
  ", page);
  				wait_on_page_writeback(page);
  			}
  			if ((snap_size && page_offset(page) > snap_size) ||
  			    (!snap_size &&
  			     page_offset(page) > i_size_read(inode))) {
  				dout("%p page eof %llu
  ", page, snap_size ?
  				     snap_size : i_size_read(inode));
  				done = 1;
  				unlock_page(page);
  				break;
  			}
  			if (PageWriteback(page)) {
  				dout("%p under writeback
  ", page);
  				unlock_page(page);
  				break;
  			}
  
  			/* only if matching snap context */

  			pgsnapc = (void *)page->private;
  			if (pgsnapc->seq > snapc->seq) {
  				dout("page snapc %p %lld > oldest %p %lld
  ",
  				     pgsnapc, pgsnapc->seq, snapc, snapc->seq);

  				unlock_page(page);
  				if (!locked_pages)
  					continue; /* keep looking for snap */
  				break;
  			}
  
  			if (!clear_page_dirty_for_io(page)) {
  				dout("%p !clear_page_dirty_for_io
  ", page);
  				unlock_page(page);
  				break;
  			}
  
  			/* ok */
  			if (locked_pages == 0) {
  				/* prepare async write request */

  				offset = (unsigned long long)page->index
  					<< PAGE_CACHE_SHIFT;

  				len = wsize;

  				req = ceph_osdc_new_request(&fsc->client->osdc,

  					    &ci->i_layout,
  					    ceph_vino(inode),
  					    offset, &len,
  					    CEPH_OSD_OP_WRITE,
  					    CEPH_OSD_FLAG_WRITE |
  						    CEPH_OSD_FLAG_ONDISK,
  					    snapc, do_sync,
  					    ci->i_truncate_seq,
  					    ci->i_truncate_size,

  					    &inode->i_mtime, true, 1, 0);

  				max_pages = req->r_num_pages;

  				alloc_page_vec(fsc, req);

  				req->r_callback = writepages_finish;
  				req->r_inode = inode;

  			}
  
  			/* note position of first page in pvec */
  			if (first < 0)
  				first = i;
  			dout("%p will write page %p idx %lu
  ",
  			     inode, page, page->index);

  			writeback_stat =

  			       atomic_long_inc_return(&fsc->writeback_count);

  			if (writeback_stat > CONGESTION_ON_THRESH(

  				    fsc->mount_options->congestion_kb)) {
  				set_bdi_congested(&fsc->backing_dev_info,

  						  BLK_RW_ASYNC);

  			}

  			set_page_writeback(page);
  			req->r_pages[locked_pages] = page;
  			locked_pages++;
  			next = page->index + 1;
  		}
  
  		/* did we get anything? */
  		if (!locked_pages)
  			goto release_pvec_pages;
  		if (i) {
  			int j;
  			BUG_ON(!locked_pages || first < 0);
  
  			if (pvec_pages && i == pvec_pages &&
  			    locked_pages < max_pages) {
  				dout("reached end pvec, trying for more
  ");
  				pagevec_reinit(&pvec);
  				goto get_more_pages;
  			}
  
  			/* shift unused pages over in the pvec...  we
  			 * will need to release them below. */
  			for (j = i; j < pvec_pages; j++) {
  				dout(" pvec leftover page %p
  ",
  				     pvec.pages[j]);
  				pvec.pages[j-i+first] = pvec.pages[j];
  			}
  			pvec.nr -= i-first;
  		}
  
  		/* submit the write */
  		offset = req->r_pages[0]->index << PAGE_CACHE_SHIFT;
  		len = min((snap_size ? snap_size : i_size_read(inode)) - offset,
  			  (u64)locked_pages << PAGE_CACHE_SHIFT);
  		dout("writepages got %d pages at %llu~%llu
  ",
  		     locked_pages, offset, len);
  
  		/* revise final length, page count */
  		req->r_num_pages = locked_pages;
  		reqhead = req->r_request->front.iov_base;
  		op = (void *)(reqhead + 1);
  		op->extent.length = cpu_to_le64(len);
  		op->payload_len = cpu_to_le32(len);
  		req->r_request->hdr.data_len = cpu_to_le32(len);

  		ceph_osdc_start_request(&fsc->client->osdc, req, true);

  		req = NULL;
  
  		/* continue? */
  		index = next;
  		wbc->nr_to_write -= locked_pages;
  		if (wbc->nr_to_write <= 0)
  			done = 1;
  
  release_pvec_pages:
  		dout("pagevec_release on %d pages (%p)
  ", (int)pvec.nr,
  		     pvec.nr ? pvec.pages[0] : NULL);
  		pagevec_release(&pvec);
  
  		if (locked_pages && !done)
  			goto retry;
  	}
  
  	if (should_loop && !done) {
  		/* more to do; loop back to beginning of file */
  		dout("writepages looping back to beginning of file
  ");
  		should_loop = 0;
  		index = 0;
  		goto retry;
  	}
  
  	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
  		mapping->writeback_index = index;
  
  out:
  	if (req)
  		ceph_osdc_put_request(req);
  	if (rc > 0)
  		rc = 0;  /* vfs expects us to return 0 */
  	ceph_put_snap_context(snapc);
  	dout("writepages done, rc = %d
  ", rc);

  	return rc;
  }
  
  
  
  /*
   * See if a given @snapc is either writeable, or already written.
   */
  static int context_is_writeable_or_written(struct inode *inode,
  					   struct ceph_snap_context *snapc)
  {
  	struct ceph_snap_context *oldest = get_oldest_context(inode, NULL);

  	int ret = !oldest || snapc->seq <= oldest->seq;
  
  	ceph_put_snap_context(oldest);
  	return ret;

  }
  
  /*
   * We are only allowed to write into/dirty the page if the page is
   * clean, or already dirty within the same snap context.

   *
   * called with page locked.
   * return success with page locked,
   * or any failure (incl -EAGAIN) with page unlocked.

   */

  static int ceph_update_writeable_page(struct file *file,
  			    loff_t pos, unsigned len,
  			    struct page *page)

  {
  	struct inode *inode = file->f_dentry->d_inode;
  	struct ceph_inode_info *ci = ceph_inode(inode);

  	struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;

  	loff_t page_off = pos & PAGE_CACHE_MASK;
  	int pos_in_page = pos & ~PAGE_CACHE_MASK;
  	int end_in_page = pos_in_page + len;
  	loff_t i_size;

  	int r;

  	struct ceph_snap_context *snapc, *oldest;

  retry_locked:
  	/* writepages currently holds page lock, but if we change that later, */
  	wait_on_page_writeback(page);
  
  	/* check snap context */
  	BUG_ON(!ci->i_snap_realm);
  	down_read(&mdsc->snap_rwsem);
  	BUG_ON(!ci->i_snap_realm->cached_context);

  	snapc = (void *)page->private;
  	if (snapc && snapc != ci->i_head_snapc) {

  		/*
  		 * this page is already dirty in another (older) snap
  		 * context!  is it writeable now?
  		 */

  		oldest = get_oldest_context(inode, NULL);

  		up_read(&mdsc->snap_rwsem);

  		if (snapc->seq > oldest->seq) {

  			ceph_put_snap_context(oldest);

  			dout(" page %p snapc %p not current or oldest
  ",

  			     page, snapc);

  			/*
  			 * queue for writeback, and wait for snapc to
  			 * be writeable or written
  			 */

  			snapc = ceph_get_snap_context(snapc);

  			unlock_page(page);

  			ceph_queue_writeback(inode);

  			r = wait_event_interruptible(ci->i_cap_wq,

  			       context_is_writeable_or_written(inode, snapc));
  			ceph_put_snap_context(snapc);

  			if (r == -ERESTARTSYS)
  				return r;

  			return -EAGAIN;

  		}

  		ceph_put_snap_context(oldest);

  
  		/* yay, writeable, do it now (without dropping page lock) */
  		dout(" page %p snapc %p not current, but oldest
  ",
  		     page, snapc);
  		if (!clear_page_dirty_for_io(page))
  			goto retry_locked;
  		r = writepage_nounlock(page, NULL);
  		if (r < 0)
  			goto fail_nosnap;
  		goto retry_locked;
  	}
  
  	if (PageUptodate(page)) {
  		dout(" page %p already uptodate
  ", page);
  		return 0;
  	}
  
  	/* full page? */
  	if (pos_in_page == 0 && len == PAGE_CACHE_SIZE)
  		return 0;
  
  	/* past end of file? */
  	i_size = inode->i_size;   /* caller holds i_mutex */
  
  	if (i_size + len > inode->i_sb->s_maxbytes) {
  		/* file is too big */
  		r = -EINVAL;
  		goto fail;
  	}
  
  	if (page_off >= i_size ||
  	    (pos_in_page == 0 && (pos+len) >= i_size &&
  	     end_in_page - pos_in_page != PAGE_CACHE_SIZE)) {
  		dout(" zeroing %p 0 - %d and %d - %d
  ",
  		     page, pos_in_page, end_in_page, (int)PAGE_CACHE_SIZE);
  		zero_user_segments(page,
  				   0, pos_in_page,
  				   end_in_page, PAGE_CACHE_SIZE);
  		return 0;
  	}
  
  	/* we need to read it. */
  	up_read(&mdsc->snap_rwsem);
  	r = readpage_nounlock(file, page);
  	if (r < 0)
  		goto fail_nosnap;
  	goto retry_locked;
  
  fail:
  	up_read(&mdsc->snap_rwsem);
  fail_nosnap:
  	unlock_page(page);
  	return r;
  }
  
  /*

   * We are only allowed to write into/dirty the page if the page is
   * clean, or already dirty within the same snap context.
   */
  static int ceph_write_begin(struct file *file, struct address_space *mapping,
  			    loff_t pos, unsigned len, unsigned flags,
  			    struct page **pagep, void **fsdata)
  {
  	struct inode *inode = file->f_dentry->d_inode;
  	struct page *page;
  	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
  	int r;
  
  	do {

  		/* get a page */

  		page = grab_cache_page_write_begin(mapping, index, 0);
  		if (!page)
  			return -ENOMEM;
  		*pagep = page;
  
  		dout("write_begin file %p inode %p page %p %d~%d
  ", file,

  		     inode, page, (int)pos, (int)len);

  
  		r = ceph_update_writeable_page(file, pos, len, page);
  	} while (r == -EAGAIN);
  
  	return r;
  }
  
  /*

   * we don't do anything in here that simple_write_end doesn't do
   * except adjust dirty page accounting and drop read lock on
   * mdsc->snap_rwsem.
   */
  static int ceph_write_end(struct file *file, struct address_space *mapping,
  			  loff_t pos, unsigned len, unsigned copied,
  			  struct page *page, void *fsdata)
  {
  	struct inode *inode = file->f_dentry->d_inode;

  	struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
  	struct ceph_mds_client *mdsc = fsc->mdsc;

  	unsigned from = pos & (PAGE_CACHE_SIZE - 1);
  	int check_cap = 0;
  
  	dout("write_end file %p inode %p page %p %d~%d (%d)
  ", file,
  	     inode, page, (int)pos, (int)copied, (int)len);
  
  	/* zero the stale part of the page if we did a short copy */
  	if (copied < len)
  		zero_user_segment(page, from+copied, len);
  
  	/* did file size increase? */
  	/* (no need for i_size_read(); we caller holds i_mutex */
  	if (pos+copied > inode->i_size)
  		check_cap = ceph_inode_set_size(inode, pos+copied);
  
  	if (!PageUptodate(page))
  		SetPageUptodate(page);
  
  	set_page_dirty(page);
  
  	unlock_page(page);
  	up_read(&mdsc->snap_rwsem);
  	page_cache_release(page);
  
  	if (check_cap)
  		ceph_check_caps(ceph_inode(inode), CHECK_CAPS_AUTHONLY, NULL);
  
  	return copied;
  }
  
  /*
   * we set .direct_IO to indicate direct io is supported, but since we
   * intercept O_DIRECT reads and writes early, this function should
   * never get called.
   */
  static ssize_t ceph_direct_io(int rw, struct kiocb *iocb,
  			      const struct iovec *iov,
  			      loff_t pos, unsigned long nr_segs)
  {
  	WARN_ON(1);
  	return -EINVAL;
  }
  
  const struct address_space_operations ceph_aops = {
  	.readpage = ceph_readpage,
  	.readpages = ceph_readpages,
  	.writepage = ceph_writepage,
  	.writepages = ceph_writepages_start,
  	.write_begin = ceph_write_begin,
  	.write_end = ceph_write_end,
  	.set_page_dirty = ceph_set_page_dirty,
  	.invalidatepage = ceph_invalidatepage,
  	.releasepage = ceph_releasepage,
  	.direct_IO = ceph_direct_io,
  };
  
  
  /*
   * vm ops
   */
  
  /*
   * Reuse write_begin here for simplicity.
   */
  static int ceph_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
  {
  	struct inode *inode = vma->vm_file->f_dentry->d_inode;
  	struct page *page = vmf->page;

  	struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;

  	loff_t off = page->index << PAGE_CACHE_SHIFT;
  	loff_t size, len;

  	int ret;
  
  	size = i_size_read(inode);
  	if (off + PAGE_CACHE_SIZE <= size)
  		len = PAGE_CACHE_SIZE;
  	else
  		len = size & ~PAGE_CACHE_MASK;
  
  	dout("page_mkwrite %p %llu~%llu page %p idx %lu
  ", inode,
  	     off, len, page, page->index);

  
  	lock_page(page);
  
  	ret = VM_FAULT_NOPAGE;
  	if ((off > size) ||
  	    (page->mapping != inode->i_mapping))
  		goto out;
  
  	ret = ceph_update_writeable_page(vma->vm_file, off, len, page);
  	if (ret == 0) {
  		/* success.  we'll keep the page locked. */

  		set_page_dirty(page);
  		up_read(&mdsc->snap_rwsem);

  		ret = VM_FAULT_LOCKED;
  	} else {

  		if (ret == -ENOMEM)
  			ret = VM_FAULT_OOM;
  		else
  			ret = VM_FAULT_SIGBUS;

  	}

  out:

  	dout("page_mkwrite %p %llu~%llu = %d
  ", inode, off, len, ret);

  	if (ret != VM_FAULT_LOCKED)
  		unlock_page(page);

  	return ret;
  }
  
  static struct vm_operations_struct ceph_vmops = {
  	.fault		= filemap_fault,
  	.page_mkwrite	= ceph_page_mkwrite,
  };
  
  int ceph_mmap(struct file *file, struct vm_area_struct *vma)
  {
  	struct address_space *mapping = file->f_mapping;
  
  	if (!mapping->a_ops->readpage)
  		return -ENOEXEC;
  	file_accessed(file);
  	vma->vm_ops = &ceph_vmops;
  	vma->vm_flags |= VM_CAN_NONLINEAR;
  	return 0;
  }