// SPDX-License-Identifier: GPL-2.0-only
/* Miscellaneous routines.
 *
 * Copyright (C) 2023 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/swap.h>
#include "internal.h"

/**
 * netfs_dirty_folio - Mark folio dirty and pin a cache object for writeback
 * @mapping: The mapping the folio belongs to.
 * @folio: The folio being dirtied.
 *
 * Set the dirty flag on a folio and pin an in-use cache object in memory so
 * that writeback can later write to it.  This is intended to be called from
 * the filesystem's ->dirty_folio() method.
 *
 * Return: true if the dirty flag was set on the folio, false otherwise.
 */
bool netfs_dirty_folio(struct address_space *mapping, struct folio *folio)
{
	struct inode *inode = mapping->host;
	struct netfs_inode *ictx = netfs_inode(inode);
	struct fscache_cookie *cookie = netfs_i_cookie(ictx);
	bool need_use = false;

	_enter("");

	if (!filemap_dirty_folio(mapping, folio))
		return false;
	if (!fscache_cookie_valid(cookie))
		return true;

	if (!(inode->i_state & I_PINNING_NETFS_WB)) {
		spin_lock(&inode->i_lock);
		if (!(inode->i_state & I_PINNING_NETFS_WB)) {
			inode->i_state |= I_PINNING_NETFS_WB;
			need_use = true;
		}
		spin_unlock(&inode->i_lock);

		if (need_use)
			fscache_use_cookie(cookie, true);
	}
	return true;
}
EXPORT_SYMBOL(netfs_dirty_folio);

/**
 * netfs_unpin_writeback - Unpin writeback resources
 * @inode: The inode on which the cookie resides
 * @wbc: The writeback control
 *
 * Unpin the writeback resources pinned by netfs_dirty_folio().  This is
 * intended to be called as/by the netfs's ->write_inode() method.
 */
int netfs_unpin_writeback(struct inode *inode, struct writeback_control *wbc)
{
	struct fscache_cookie *cookie = netfs_i_cookie(netfs_inode(inode));

	if (wbc->unpinned_netfs_wb)
		fscache_unuse_cookie(cookie, NULL, NULL);
	return 0;
}
EXPORT_SYMBOL(netfs_unpin_writeback);

/**
 * netfs_clear_inode_writeback - Clear writeback resources pinned by an inode
 * @inode: The inode to clean up
 * @aux: Auxiliary data to apply to the inode
 *
 * Clear any writeback resources held by an inode when the inode is evicted.
 * This must be called before clear_inode() is called.
 */
void netfs_clear_inode_writeback(struct inode *inode, const void *aux)
{
	struct fscache_cookie *cookie = netfs_i_cookie(netfs_inode(inode));

	if (inode->i_state & I_PINNING_NETFS_WB) {
		loff_t i_size = i_size_read(inode);
		fscache_unuse_cookie(cookie, aux, &i_size);
	}
}
EXPORT_SYMBOL(netfs_clear_inode_writeback);

/**
 * netfs_invalidate_folio - Invalidate or partially invalidate a folio
 * @folio: Folio proposed for release
 * @offset: Offset of the invalidated region
 * @length: Length of the invalidated region
 *
 * Invalidate part or all of a folio for a network filesystem.  The folio will
 * be removed afterwards if the invalidated region covers the entire folio.
 */
void netfs_invalidate_folio(struct folio *folio, size_t offset, size_t length)
{
	struct netfs_folio *finfo;
	struct netfs_inode *ctx = netfs_inode(folio_inode(folio));
	size_t flen = folio_size(folio);

	_enter("{%lx},%zx,%zx", folio->index, offset, length);

	if (offset == 0 && length == flen) {
		unsigned long long i_size = i_size_read(&ctx->inode);
		unsigned long long fpos = folio_pos(folio), end;

		end = umin(fpos + flen, i_size);
		if (fpos < i_size && end > ctx->zero_point)
			ctx->zero_point = end;
	}

	folio_wait_private_2(folio); /* [DEPRECATED] */

	if (!folio_test_private(folio))
		return;

	finfo = netfs_folio_info(folio);

	if (offset == 0 && length >= flen)
		goto erase_completely;

	if (finfo) {
		/* We have a partially uptodate page from a streaming write. */
		unsigned int fstart = finfo->dirty_offset;
		unsigned int fend = fstart + finfo->dirty_len;
		unsigned int iend = offset + length;

		if (offset >= fend)
			return;
		if (iend <= fstart)
			return;

		/* The invalidation region overlaps the data.  If the region
		 * covers the start of the data, we either move along the start
		 * or just erase the data entirely.
		 */
		if (offset <= fstart) {
			if (iend >= fend)
				goto erase_completely;
			/* Move the start of the data. */
			finfo->dirty_len = fend - iend;
			finfo->dirty_offset = offset;
			return;
		}

		/* Reduce the length of the data if the invalidation region
		 * covers the tail part.
		 */
		if (iend >= fend) {
			finfo->dirty_len = offset - fstart;
			return;
		}

		/* A partial write was split.  The caller has already zeroed
		 * it, so just absorb the hole.
		 */
	}
	return;

erase_completely:
	netfs_put_group(netfs_folio_group(folio));
	folio_detach_private(folio);
	folio_clear_uptodate(folio);
	kfree(finfo);
	return;
}
EXPORT_SYMBOL(netfs_invalidate_folio);

/**
 * netfs_release_folio - Try to release a folio
 * @folio: Folio proposed for release
 * @gfp: Flags qualifying the release
 *
 * Request release of a folio and clean up its private state if it's not busy.
 * Returns true if the folio can now be released, false if not
 */
bool netfs_release_folio(struct folio *folio, gfp_t gfp)
{
	struct netfs_inode *ctx = netfs_inode(folio_inode(folio));
	unsigned long long end;

	if (folio_test_dirty(folio))
		return false;

	end = umin(folio_pos(folio) + folio_size(folio), i_size_read(&ctx->inode));
	if (end > ctx->zero_point)
		ctx->zero_point = end;

	if (folio_test_private(folio))
		return false;
	if (unlikely(folio_test_private_2(folio))) { /* [DEPRECATED] */
		if (current_is_kswapd() || !(gfp & __GFP_FS))
			return false;
		folio_wait_private_2(folio);
	}
	fscache_note_page_release(netfs_i_cookie(ctx));
	return true;
}
EXPORT_SYMBOL(netfs_release_folio);