path: root/fs/cachefiles/rdwr.c

/* Storage object read/write
 *
 * 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 Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#include <linux/mount.h>
#include <linux/slab.h>
#include <linux/file.h>
#include "internal.h"

/*
 * detect wake up events generated by the unlocking of pages in which we're
 * interested
 * - we use this to detect read completion of backing pages
 * - the caller holds the waitqueue lock
 */
static int cachefiles_read_waiter(wait_queue_t *wait, unsigned mode,
				  int sync, void *_key)
{
	struct cachefiles_one_read *monitor =
		container_of(wait, struct cachefiles_one_read, monitor);
	struct cachefiles_object *object;
	struct wait_bit_key *key = _key;
	struct page *page = wait->private;

	ASSERT(key);

	_enter("{%lu},%u,%d,{%p,%u}",
	       monitor->netfs_page->index, mode, sync,
	       key->flags, key->bit_nr);

	if (key->flags != &page->flags ||
	    key->bit_nr != PG_locked)
		return 0;

	_debug("--- monitor %p %lx ---", page, page->flags);

	if (!PageUptodate(page) && !PageError(page)) {
		/* unlocked, not uptodate and not erronous? */
		_debug("page probably truncated");
	}

	/* remove from the waitqueue */
	list_del(&wait->task_list);

	/* move onto the action list and queue for FS-Cache thread pool */
	ASSERT(monitor->op);

	object = container_of(monitor->op->op.object,
			      struct cachefiles_object, fscache);

	spin_lock(&object->work_lock);
	list_add_tail(&monitor->op_link, &monitor->op->to_do);
	spin_unlock(&object->work_lock);

	fscache_enqueue_retrieval(monitor->op);
	return 0;
}

/*
 * handle a probably truncated page
 * - check to see if the page is still relevant and reissue the read if
 *   possible
 * - return -EIO on error, -ENODATA if the page is gone, -EINPROGRESS if we
 *   must wait again and 0 if successful
 */
static int cachefiles_read_reissue(struct cachefiles_object *object,
				   struct cachefiles_one_read *monitor)
{
	struct address_space *bmapping = object->backer->d_inode->i_mapping;
	struct page *backpage = monitor->back_page, *backpage2;
	int ret;

	kenter("{ino=%lx},{%lx,%lx}",
	       object->backer->d_inode->i_ino,
	       backpage->index, backpage->flags);

	/* skip if the page was truncated away completely */
	if (backpage->mapping != bmapping) {
		kleave(" = -ENODATA [mapping]");
		return -ENODATA;
	}

	backpage2 = find_get_page(bmapping, backpage->index);
	if (!backpage2) {
		kleave(" = -ENODATA [gone]");
		return -ENODATA;
	}

	if (backpage != backpage2) {
		put_page(backpage2);
		kleave(" = -ENODATA [different]");
		return -ENODATA;
	}

	/* the page is still there and we already have a ref on it, so we don't
	 * need a second */
	put_page(backpage2);

	INIT_LIST_HEAD(&monitor->op_link);
	add_page_wait_queue(backpage, &monitor->monitor);

	if (trylock_page(backpage)) {
		ret = -EIO;
		if (PageError(backpage))
			goto unlock_discard;
		ret = 0;
		if (PageUptodate(backpage))
			goto unlock_discard;

		kdebug("reissue read");
		ret = bmapping->a_ops->readpage(NULL, backpage);
		if (ret < 0)
			goto unlock_discard;
	}

	/* but the page may have been read before the monitor was installed, so
	 * the monitor may miss the event - so we have to ensure that we do get
	 * one in such a case */
	if (trylock_page(backpage)) {
		_debug("jumpstart %p {%lx}", backpage, backpage->flags);
		unlock_page(backpage);
	}

	/* it'll reappear on the todo list */
	kleave(" = -EINPROGRESS");
	return -EINPROGRESS;

unlock_discard:
	unlock_page(backpage);
	spin_lock_irq(&object->work_lock);
	list_del(&monitor->op_link);
	spin_unlock_irq(&object->work_lock);
	kleave(" = %d", ret);
	return ret;
}

/*
 * copy data from backing pages to netfs pages to complete a read operation
 * - driven by FS-Cache's thread pool
 */
static void cachefiles_read_copier(struct fscache_operation *_op)
{
	struct cachefiles_one_read *monitor;
	struct cachefiles_object *object;
	struct fscache_retrieval *op;
	struct pagevec pagevec;
	int error, max;

	op = container_of(_op, struct fscache_retrieval, op);
	object = container_of(op->op.object,
			      struct cachefiles_object, fscache);

	_enter("{ino=%lu}", object->backer->d_inode->i_ino);

	pagevec_init(&pagevec, 0);

	max =