/* handling of writes to regular files and writing back to the server
   *
   * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)
   *
   * 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.
   */
  #include <linux/backing-dev.h>
  #include <linux/slab.h>
  #include <linux/fs.h>
  #include <linux/pagemap.h>
  #include <linux/writeback.h>
  #include <linux/pagevec.h>
  #include <linux/aio.h>
  #include "internal.h"
  
  static int afs_write_back_from_locked_page(struct afs_writeback *wb,
  					   struct page *page);
  
  /*
   * mark a page as having been made dirty and thus needing writeback
   */
  int afs_set_page_dirty(struct page *page)
  {
  	_enter("");
  	return __set_page_dirty_nobuffers(page);
  }
  
  /*
   * unlink a writeback record because its usage has reached zero
   * - must be called with the wb->vnode->writeback_lock held
   */
  static void afs_unlink_writeback(struct afs_writeback *wb)
  {
  	struct afs_writeback *front;
  	struct afs_vnode *vnode = wb->vnode;
  
  	list_del_init(&wb->link);
  	if (!list_empty(&vnode->writebacks)) {
  		/* if an fsync rises to the front of the queue then wake it
  		 * up */
  		front = list_entry(vnode->writebacks.next,
  				   struct afs_writeback, link);
  		if (front->state == AFS_WBACK_SYNCING) {
  			_debug("wake up sync");
  			front->state = AFS_WBACK_COMPLETE;
  			wake_up(&front->waitq);
  		}
  	}
  }
  
  /*
   * free a writeback record
   */
  static void afs_free_writeback(struct afs_writeback *wb)
  {
  	_enter("");
  	key_put(wb->key);
  	kfree(wb);
  }
  
  /*
   * dispose of a reference to a writeback record
   */
  void afs_put_writeback(struct afs_writeback *wb)
  {
  	struct afs_vnode *vnode = wb->vnode;
  
  	_enter("{%d}", wb->usage);
  
  	spin_lock(&vnode->writeback_lock);
  	if (--wb->usage == 0)
  		afs_unlink_writeback(wb);
  	else
  		wb = NULL;
  	spin_unlock(&vnode->writeback_lock);
  	if (wb)
  		afs_free_writeback(wb);
  }
  
  /*
   * partly or wholly fill a page that's under preparation for writing
   */
  static int afs_fill_page(struct afs_vnode *vnode, struct key *key,
  			 loff_t pos, struct page *page)
  {
  	loff_t i_size;
  	int ret;
  	int len;
  
  	_enter(",,%llu", (unsigned long long)pos);
  
  	i_size = i_size_read(&vnode->vfs_inode);
  	if (pos + PAGE_CACHE_SIZE > i_size)
  		len = i_size - pos;
  	else
  		len = PAGE_CACHE_SIZE;
  
  	ret = afs_vnode_fetch_data(vnode, key, pos, len, page);
  	if (ret < 0) {
  		if (ret == -ENOENT) {
  			_debug("got NOENT from server"
  			       " - marking file deleted and stale");
  			set_bit(AFS_VNODE_DELETED, &vnode->flags);
  			ret = -ESTALE;
  		}
  	}
  
  	_leave(" = %d", ret);
  	return ret;
  }
  
  /*
   * prepare to perform part of a write to a page
   */
  int afs_write_begin(struct file *file, struct address_space *mapping,
  		    loff_t pos, unsigned len, unsigned flags,
  		    struct page **pagep, void **fsdata)
  {
  	struct afs_writeback *candidate, *wb;
  	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
  	struct page *page;
  	struct key *key = file->private_data;
  	unsigned from = pos & (PAGE_CACHE_SIZE - 1);
  	unsigned to = from + len;
  	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
  	int ret;
  
  	_enter("{%x:%u},{%lx},%u,%u",
  	       vnode->fid.vid, vnode->fid.vnode, index, from, to);
  
  	candidate = kzalloc(sizeof(*candidate), GFP_KERNEL);
  	if (!candidate)
  		return -ENOMEM;
  	candidate->vnode = vnode;
  	candidate->first = candidate->last = index;
  	candidate->offset_first = from;
  	candidate->to_last = to;
  	INIT_LIST_HEAD(&candidate->link);
  	candidate->usage = 1;
  	candidate->state = AFS_WBACK_PENDING;
  	init_waitqueue_head(&candidate->waitq);
  
  	page = grab_cache_page_write_begin(mapping, index, flags);
  	if (!page) {
  		kfree(candidate);
  		return -ENOMEM;
  	}
  	*pagep = page;
  	/* page won't leak in error case: it eventually gets cleaned off LRU */
  
  	if (!PageUptodate(page) && len != PAGE_CACHE_SIZE) {
  		ret = afs_fill_page(vnode, key, index << PAGE_CACHE_SHIFT, page);
  		if (ret < 0) {
  			kfree(candidate);
  			_leave(" = %d [prep]", ret);
  			return ret;
  		}
  		SetPageUptodate(page);
  	}
  
  try_again:
  	spin_lock(&vnode->writeback_lock);
  
  	/* see if this page is already pending a writeback under a suitable key
  	 * - if so we can just join onto that one */
  	wb = (struct afs_writeback *) page_private(page);
  	if (wb) {
  		if (wb->key == key && wb->state == AFS_WBACK_PENDING)
  			goto subsume_in_current_wb;
  		goto flush_conflicting_wb;
  	}
  
  	if (index > 0) {
  		/* see if we can find an already pending writeback that we can
  		 * append this page to */
  		list_for_each_entry(wb, &vnode->writebacks, link) {
  			if (wb->last == index - 1 && wb->key == key &&
  			    wb->state == AFS_WBACK_PENDING)
  				goto append_to_previous_wb;
  		}
  	}
  
  	list_add_tail(&candidate->link, &vnode->writebacks);
  	candidate->key = key_get(key);
  	spin_unlock(&vnode->writeback_lock);
  	SetPagePrivate(page);
  	set_page_private(page, (unsigned long) candidate);
  	_leave(" = 0 [new]");
  	return 0;
  
  subsume_in_current_wb:
  	_debug("subsume");
  	ASSERTRANGE(wb->first, <=, index, <=, wb->last);
  	if (index == wb->first && from < wb->offset_first)
  		wb->offset_first = from;
  	if (index == wb->last && to > wb->to_last)
  		wb->to_last = to;
  	spin_unlock(&vnode->writeback_lock);
  	kfree(candidate);
  	_leave(" = 0 [sub]");
  	return 0;
  
  append_to_previous_wb:
  	_debug("append into %lx-%lx", wb->first, wb->last);
  	wb->usage++;
  	wb->last++;
  	wb->to_last = to;
  	spin_unlock(&vnode->writeback_lock);
  	SetPagePrivate(page);
  	set_page_private(page, (unsigned long) wb);
  	kfree(candidate);
  	_leave(" = 0 [app]");
  	return 0;
  
  	/* the page is currently bound to another context, so if it's dirty we
  	 * need to flush it before we can use the new context */
  flush_conflicting_wb:
  	_debug("flush conflict");
  	if (wb->state == AFS_WBACK_PENDING)
  		wb->state = AFS_WBACK_CONFLICTING;
  	spin_unlock(&vnode->writeback_lock);
  	if (PageDirty(page)) {
  		ret = afs_write_back_from_locked_page(wb, page);
  		if (ret < 0) {
  			afs_put_writeback(candidate);
  			_leave(" = %d", ret);
  			return ret;
  		}
  	}
  
  	/* the page holds a ref on the writeback record */
  	afs_put_writeback(wb);
  	set_page_private(page, 0);
  	ClearPagePrivate(page);
  	goto try_again;
  }
  
  /*
   * finalise part of a write to a page
   */
  int afs_write_end(struct file *file, struct address_space *mapping,
  		  loff_t pos, unsigned len, unsigned copied,
  		  struct page *page, void *fsdata)
  {
  	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
  	loff_t i_size, maybe_i_size;
  
  	_enter("{%x:%u},{%lx}",
  	       vnode->fid.vid, vnode->fid.vnode, page->index);
  
  	maybe_i_size = pos + copied;
  
  	i_size = i_size_read(&vnode->vfs_inode);
  	if (maybe_i_size > i_size) {
  		spin_lock(&vnode->writeback_lock);
  		i_size = i_size_read(&vnode->vfs_inode);
  		if (maybe_i_size > i_size)
  			i_size_write(&vnode->vfs_inode, maybe_i_size);
  		spin_unlock(&vnode->writeback_lock);
  	}
  
  	set_page_dirty(page);
  	if (PageDirty(page))
  		_debug("dirtied");
  	unlock_page(page);
  	page_cache_release(page);
  
  	return copied;
  }
  
  /*
   * kill all the pages in the given range
   */
  static void afs_kill_pages(struct afs_vnode *vnode, bool error,
  			   pgoff_t first, pgoff_t last)
  {
  	struct pagevec pv;
  	unsigned count, loop;
  
  	_enter("{%x:%u},%lx-%lx",
  	       vnode->fid.vid, vnode->fid.vnode, first, last);
  
  	pagevec_init(&pv, 0);
  
  	do {
  		_debug("kill %lx-%lx", first, last);
  
  		count = last - first + 1;
  		if (count > PAGEVEC_SIZE)
  			count = PAGEVEC_SIZE;
  		pv.nr = find_get_pages_contig(vnode->vfs_inode.i_mapping,
  					      first, count, pv.pages);
  		ASSERTCMP(pv.nr, ==, count);
  
  		for (loop = 0; loop < count; loop++) {
  			ClearPageUptodate(pv.pages[loop]);
  			if (error)
  				SetPageError(pv.pages[loop]);
  			end_page_writeback(pv.pages[loop]);
  		}
  
  		__pagevec_release(&pv);
  	} while (first < last);
  
  	_leave("");
  }
  
  /*
   * synchronously write back the locked page and any subsequent non-locked dirty
   * pages also covered by the same writeback record
   */
  static int afs_write_back_from_locked_page(struct afs_writeback *wb,
  					   struct page *primary_page)
  {
  	struct page *pages[8], *page;
  	unsigned long count;
  	unsigned n, offset, to;
  	pgoff_t start, first, last;
  	int loop, ret;
  
  	_enter(",%lx", primary_page->index);
  
  	count = 1;
  	if (!clear_page_dirty_for_io(primary_page))
  		BUG();
  	if (test_set_page_writeback(primary_page))
  		BUG();
  
  	/* find all consecutive lockable dirty pages, stopping when we find a
  	 * page that is not immediately lockable, is not dirty or is missing,
  	 * or we reach the end of the range */
  	start = primary_page->index;
  	if (start >= wb->last)
  		goto no_more;
  	start++;
  	do {
  		_debug("more %lx [%lx]", start, count);
  		n = wb->last - start + 1;
  		if (n > ARRAY_SIZE(pages))
  			n = ARRAY_SIZE(pages);
  		n = find_get_pages_contig(wb->vnode->vfs_inode.i_mapping,
  					  start, n, pages);
  		_debug("fgpc %u", n);
  		if (n == 0)
  			goto no_more;
  		if (pages[0]->index != start) {
  			do {
  				put_page(pages[--n]);
  			} while (n > 0);
  			goto no_more;
  		}
  
  		for (loop = 0; loop < n; loop++) {
  			page = pages[loop];
  			if (page->index > wb->last)
  				break;
  			if (!trylock_page(page))
  				break;
  			if (!PageDirty(page) ||
  			    page_private(page) != (unsigned long) wb) {
  				unlock_page(page);
  				break;
  			}
  			if (!clear_page_dirty_for_io(page))
  				BUG();
  			if (test_set_page_writeback(page))
  				BUG();
  			unlock_page(page);
  			put_page(page);
  		}
  		count += loop;
  		if (loop < n) {
  			for (; loop < n; loop++)
  				put_page(pages[loop]);
  			goto no_more;
  		}
  
  		start += loop;
  	} while (start <= wb->last && count < 65536);
  
  no_more:
  	/* we now have a contiguous set of dirty pages, each with writeback set
  	 * and the dirty mark cleared; the first page is locked and must remain
  	 * so, all the rest are unlocked */
  	first = primary_page->index;
  	last = first + count - 1;
  
  	offset = (first == wb->first) ? wb->offset_first : 0;
  	to = (last == wb->last) ? wb->to_last : PAGE_SIZE;
  
  	_debug("write back %lx[%u..] to %lx[..%u]", first, offset, last, to);
  
  	ret = afs_vnode_store_data(wb, first, last, offset, to);
  	if (ret < 0) {
  		switch (ret) {
  		case -EDQUOT:
  		case -ENOSPC:
  			set_bit(AS_ENOSPC,
  				&wb->vnode->vfs_inode.i_mapping->flags);
  			break;
  		case -EROFS:
  		case -EIO:
  		case -EREMOTEIO:
  		case -EFBIG:
  		case -ENOENT:
  		case -ENOMEDIUM:
  		case -ENXIO:
  			afs_kill_pages(wb->vnode, true, first, last);
  			set_bit(AS_EIO, &wb->vnode->vfs_inode.i_mapping->flags);
  			break;
  		case -EACCES:
  		case -EPERM:
  		case -ENOKEY:
  		case -EKEYEXPIRED:
  		case -EKEYREJECTED:
  		case -EKEYREVOKED:
  			afs_kill_pages(wb->vnode, false, first, last);
  			break;
  		default:
  			break;
  		}
  	} else {
  		ret = count;
  	}
  
  	_leave(" = %d", ret);
  	return ret;
  }
  
  /*
   * write a page back to the server
   * - the caller locked the page for us
   */
  int afs_writepage(struct page *page, struct writeback_control *wbc)
  {
  	struct afs_writeback *wb;
  	int ret;
  
  	_enter("{%lx},", page->index);
  
  	wb = (struct afs_writeback *) page_private(page);
  	ASSERT(wb != NULL);
  
  	ret = afs_write_back_from_locked_page(wb, page);
  	unlock_page(page);
  	if (ret < 0) {
  		_leave(" = %d", ret);
  		return 0;
  	}
  
  	wbc->nr_to_write -= ret;
  
  	_leave(" = 0");
  	return 0;
  }
  
  /*
   * write a region of pages back to the server
   */
  static int afs_writepages_region(struct address_space *mapping,
  				 struct writeback_control *wbc,
  				 pgoff_t index, pgoff_t end, pgoff_t *_next)
  {
  	struct afs_writeback *wb;
  	struct page *page;
  	int ret, n;
  
  	_enter(",,%lx,%lx,", index, end);
  
  	do {
  		n = find_get_pages_tag(mapping, &index, PAGECACHE_TAG_DIRTY,
  				       1, &page);
  		if (!n)
  			break;
  
  		_debug("wback %lx", page->index);
  
  		if (page->index > end) {
  			*_next = index;
  			page_cache_release(page);
  			_leave(" = 0 [%lx]", *_next);
  			return 0;
  		}
  
  		/* at this point we hold neither mapping->tree_lock nor lock on
  		 * the page itself: the page may be truncated or invalidated
  		 * (changing page->mapping to NULL), or even swizzled back from
  		 * swapper_space to tmpfs file mapping
  		 */
  		lock_page(page);
  
  		if (page->mapping != mapping) {
  			unlock_page(page);
  			page_cache_release(page);
  			continue;
  		}
  
  		if (wbc->sync_mode != WB_SYNC_NONE)
  			wait_on_page_writeback(page);
  
  		if (PageWriteback(page) || !PageDirty(page)) {
  			unlock_page(page);
  			continue;
  		}
  
  		wb = (struct afs_writeback *) page_private(page);
  		ASSERT(wb != NULL);
  
  		spin_lock(&wb->vnode->writeback_lock);
  		wb->state = AFS_WBACK_WRITING;
  		spin_unlock(&wb->vnode->writeback_lock);
  
  		ret = afs_write_back_from_locked_page(wb, page);
  		unlock_page(page);
  		page_cache_release(page);
  		if (ret < 0) {
  			_leave(" = %d", ret);
  			return ret;
  		}
  
  		wbc->nr_to_write -= ret;
  
  		cond_resched();
  	} while (index < end && wbc->nr_to_write > 0);
  
  	*_next = index;
  	_leave(" = 0 [%lx]", *_next);
  	return 0;
  }
  
  /*
   * write some of the pending data back to the server
   */
  int afs_writepages(struct address_space *mapping,
  		   struct writeback_control *wbc)
  {
  	pgoff_t start, end, next;
  	int ret;
  
  	_enter("");
  
  	if (wbc->range_cyclic) {
  		start = mapping->writeback_index;
  		end = -1;
  		ret = afs_writepages_region(mapping, wbc, start, end, &next);
  		if (start > 0 && wbc->nr_to_write > 0 && ret == 0)
  			ret = afs_writepages_region(mapping, wbc, 0, start,
  						    &next);
  		mapping->writeback_index = next;
  	} else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
  		end = (pgoff_t)(LLONG_MAX >> PAGE_CACHE_SHIFT);
  		ret = afs_writepages_region(mapping, wbc, 0, end, &next);
  		if (wbc->nr_to_write > 0)
  			mapping->writeback_index = next;
  	} else {
  		start = wbc->range_start >> PAGE_CACHE_SHIFT;
  		end = wbc->range_end >> PAGE_CACHE_SHIFT;
  		ret = afs_writepages_region(mapping, wbc, start, end, &next);
  	}
  
  	_leave(" = %d", ret);
  	return ret;
  }
  
  /*
   * completion of write to server
   */
  void afs_pages_written_back(struct afs_vnode *vnode, struct afs_call *call)
  {
  	struct afs_writeback *wb = call->wb;
  	struct pagevec pv;
  	unsigned count, loop;
  	pgoff_t first = call->first, last = call->last;
  	bool free_wb;
  
  	_enter("{%x:%u},{%lx-%lx}",
  	       vnode->fid.vid, vnode->fid.vnode, first, last);
  
  	ASSERT(wb != NULL);
  
  	pagevec_init(&pv, 0);
  
  	do {
  		_debug("done %lx-%lx", first, last);
  
  		count = last - first + 1;
  		if (count > PAGEVEC_SIZE)
  			count = PAGEVEC_SIZE;
  		pv.nr = find_get_pages_contig(call->mapping, first, count,
  					      pv.pages);
  		ASSERTCMP(pv.nr, ==, count);
  
  		spin_lock(&vnode->writeback_lock);
  		for (loop = 0; loop < count; loop++) {
  			struct page *page = pv.pages[loop];
  			end_page_writeback(page);
  			if (page_private(page) == (unsigned long) wb) {
  				set_page_private(page, 0);
  				ClearPagePrivate(page);
  				wb->usage--;
  			}
  		}
  		free_wb = false;
  		if (wb->usage == 0) {
  			afs_unlink_writeback(wb);
  			free_wb = true;
  		}
  		spin_unlock(&vnode->writeback_lock);
  		first += count;
  		if (free_wb) {
  			afs_free_writeback(wb);
  			wb = NULL;
  		}
  
  		__pagevec_release(&pv);
  	} while (first <= last);
  
  	_leave("");
  }
  
  /*
   * write to an AFS file
   */
  ssize_t afs_file_write(struct kiocb *iocb, const struct iovec *iov,
  		       unsigned long nr_segs, loff_t pos)
  {
  	struct afs_vnode *vnode = AFS_FS_I(file_inode(iocb->ki_filp));
  	ssize_t result;
  	size_t count = iov_length(iov, nr_segs);
  
  	_enter("{%x.%u},{%zu},%lu,",
  	       vnode->fid.vid, vnode->fid.vnode, count, nr_segs);
  
  	if (IS_SWAPFILE(&vnode->vfs_inode)) {
  		printk(KERN_INFO
  		       "AFS: Attempt to write to active swap file!
  ");
  		return -EBUSY;
  	}
  
  	if (!count)
  		return 0;
  
  	result = generic_file_aio_write(iocb, iov, nr_segs, pos);
  	if (IS_ERR_VALUE(result)) {
  		_leave(" = %zd", result);
  		return result;
  	}
  
  	_leave(" = %zd", result);
  	return result;
  }
  
  /*
   * flush the vnode to the fileserver
   */
  int afs_writeback_all(struct afs_vnode *vnode)
  {
  	struct address_space *mapping = vnode->vfs_inode.i_mapping;
  	struct writeback_control wbc = {
  		.sync_mode	= WB_SYNC_ALL,
  		.nr_to_write	= LONG_MAX,
  		.range_cyclic	= 1,
  	};
  	int ret;
  
  	_enter("");
  
  	ret = mapping->a_ops->writepages(mapping, &wbc);
  	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
  
  	_leave(" = %d", ret);
  	return ret;
  }
  
  /*
   * flush any dirty pages for this process, and check for write errors.
   * - the return status from this call provides a reliable indication of
   *   whether any write errors occurred for this process.
   */
  int afs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
  {
  	struct dentry *dentry = file->f_path.dentry;
  	struct inode *inode = file->f_mapping->host;
  	struct afs_writeback *wb, *xwb;
  	struct afs_vnode *vnode = AFS_FS_I(dentry->d_inode);
  	int ret;
  
  	_enter("{%x:%u},{n=%s},%d",
  	       vnode->fid.vid, vnode->fid.vnode, dentry->d_name.name,
  	       datasync);
  
  	ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
  	if (ret)
  		return ret;
  	mutex_lock(&inode->i_mutex);
  
  	/* use a writeback record as a marker in the queue - when this reaches
  	 * the front of the queue, all the outstanding writes are either
  	 * completed or rejected */
  	wb = kzalloc(sizeof(*wb), GFP_KERNEL);
  	if (!wb) {
  		ret = -ENOMEM;
  		goto out;
  	}
  	wb->vnode = vnode;
  	wb->first = 0;
  	wb->last = -1;
  	wb->offset_first = 0;
  	wb->to_last = PAGE_SIZE;
  	wb->usage = 1;
  	wb->state = AFS_WBACK_SYNCING;
  	init_waitqueue_head(&wb->waitq);
  
  	spin_lock(&vnode->writeback_lock);
  	list_for_each_entry(xwb, &vnode->writebacks, link) {
  		if (xwb->state == AFS_WBACK_PENDING)
  			xwb->state = AFS_WBACK_CONFLICTING;
  	}
  	list_add_tail(&wb->link, &vnode->writebacks);
  	spin_unlock(&vnode->writeback_lock);
  
  	/* push all the outstanding writebacks to the server */
  	ret = afs_writeback_all(vnode);
  	if (ret < 0) {
  		afs_put_writeback(wb);
  		_leave(" = %d [wb]", ret);
  		goto out;
  	}
  
  	/* wait for the preceding writes to actually complete */
  	ret = wait_event_interruptible(wb->waitq,
  				       wb->state == AFS_WBACK_COMPLETE ||
  				       vnode->writebacks.next == &wb->link);
  	afs_put_writeback(wb);
  	_leave(" = %d", ret);
  out:
  	mutex_unlock(&inode->i_mutex);
  	return ret;
  }
  
  /*
   * notification that a previously read-only page is about to become writable
   * - if it returns an error, the caller will deliver a bus error signal
   */
  int afs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
  {
  	struct afs_vnode *vnode = AFS_FS_I(vma->vm_file->f_mapping->host);
  
  	_enter("{{%x:%u}},{%lx}",
  	       vnode->fid.vid, vnode->fid.vnode, page->index);
  
  	/* wait for the page to be written to the cache before we allow it to
  	 * be modified */
  #ifdef CONFIG_AFS_FSCACHE
  	fscache_wait_on_page_write(vnode->cache, page);
  #endif
  
  	_leave(" = 0");
  	return 0;
  }