alistair23-linux/fs/squashfs/file_direct.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2013
 * Phillip Lougher <phillip@squashfs.org.uk>
 */

#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/pagemap.h>
#include <linux/mutex.h>

#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs_fs_i.h"
#include "squashfs.h"
#include "page_actor.h"

static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
	int pages, struct page **page, int bytes);

/* Read separately compressed datablock directly into page cache */
int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
	int expected)

{
	struct inode *inode = target_page->mapping->host;
	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;

	int file_end = (i_size_read(inode) - 1) >> PAGE_SHIFT;
	int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
	int start_index = target_page->index & ~mask;
	int end_index = start_index | mask;
	int i, n, pages, missing_pages, bytes, res = -ENOMEM;
	struct page **page;
	struct squashfs_page_actor *actor;
	void *pageaddr;

	if (end_index > file_end)
		end_index = file_end;

	pages = end_index - start_index + 1;

	page = kmalloc_array(pages, sizeof(void *), GFP_KERNEL);
	if (page == NULL)
		return res;

	/*
	 * Create a "page actor" which will kmap and kunmap the
	 * page cache pages appropriately within the decompressor
	 */
	actor = squashfs_page_actor_init_special(page, pages, 0);
	if (actor == NULL)
		goto out;

	/* Try to grab all the pages covered by the Squashfs block */
	for (missing_pages = 0, i = 0, n = start_index; i < pages; i++, n++) {
		page[i] = (n == target_page->index) ? target_page :
			grab_cache_page_nowait(target_page->mapping, n);

		if (page[i] == NULL) {
			missing_pages++;
			continue;
		}

		if (PageUptodate(page[i])) {
			unlock_page(page[i]);
			put_page(page[i]);
			page[i] = NULL;
			missing_pages++;
		}
	}

	if (missing_pages) {
		/*
		 * Couldn't get one or more pages, this page has either
		 * been VM reclaimed, but others are still in the page cache
		 * and uptodate, or we're racing with another thread in
		 * squashfs_readpage also trying to grab them.  Fall back to
		 * using an intermediate buffer.
		 */
		res = squashfs_read_cache(target_page, block, bsize, pages,
							page, expected);
		if (res < 0)
			goto mark_errored;

		goto out;
	}

	/* Decompress directly into the page cache buffers */
	res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
	if (res < 0)
		goto mark_errored;

	if (res != expected) {
		res = -EIO;
		goto mark_errored;
	}

	/* Last page may have trailing bytes not filled */
	bytes = res % PAGE_SIZE;
	if (bytes) {
		pageaddr = kmap_atomic(page[pages - 1]);
		memset(pageaddr + bytes, 0, PAGE_SIZE - bytes);
		kunmap_atomic(pageaddr);
	}

	/* Mark pages as uptodate, unlock and release */
	for (i = 0; i < pages; i++) {
		flush_dcache_page(page[i]);
		SetPageUptodate(page[i]);
		unlock_page(page[i]);
		if (page[i] != target_page)
			put_page(page[i]);
	}

	kfree(actor);
	kfree(page);

	return 0;

mark_errored:
	/* Decompression failed, mark pages as errored.  Target_page is
	 * dealt with by the caller
	 */
	for (i = 0; i < pages; i++) {
		if (page[i] == NULL || page[i] == target_page)
			continue;
		flush_dcache_page(page[i]);
		SetPageError(page[i]);
		unlock_page(page[i]);
		put_page(page[i]);
	}

out:
	kfree(actor);
	kfree(page);
	return res;
}


static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
	int pages, struct page **page, int bytes)
{
	struct inode *i = target_page->mapping->host;
	struct squashfs_cache_entry *buffer = squashfs_get_datablock(i->i_sb,
						 block, bsize);
	int res = buffer->error, n, offset = 0;

	if (res) {
		ERROR("Unable to read page, block %llx, size %x\n", block,
			bsize);
		goto out;
	}

	for (n = 0; n < pages && bytes > 0; n++,
			bytes -= PAGE_SIZE, offset += PAGE_SIZE) {
		int avail = min_t(int, bytes, PAGE_SIZE);

		if (page[n] == NULL)
			continue;

		squashfs_fill_page(page[n], buffer, offset, avail);
		unlock_page(page[n]);
		if (page[n] != target_page)
			put_page(page[n]);
	}

out:
	squashfs_cache_put(buffer);
	return res;
}