// SPDX-License-Identifier: GPL-2.0
/*
* fs/mpage.c
*
* Copyright (C) 2002, Linus Torvalds.
*
* Contains functions related to preparing and submitting BIOs which contain
* multiple pagecache pages.
*
* 15May2002 Andrew Morton
* Initial version
* 27Jun2002 [email protected]
* use bio_add_page() to build bio's just the right size
*/
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/kdev_t.h>
#include <linux/gfp.h>
#include <linux/bio.h>
#include <linux/fs.h>
#include <linux/buffer_head.h>
#include <linux/blkdev.h>
#include <linux/highmem.h>
#include <linux/prefetch.h>
#include <linux/mpage.h>
#include <linux/mm_inline.h>
#include <linux/writeback.h>
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
#include "internal.h"
/*
* I/O completion handler for multipage BIOs.
*
* The mpage code never puts partial pages into a BIO (except for end-of-file).
* If a page does not map to a contiguous run of blocks then it simply falls
* back to block_read_full_folio().
*
* Why is this? If a page's completion depends on a number of different BIOs
* which can complete in any order (or at the same time) then determining the
* status of that page is hard. See end_buffer_async_read() for the details.
* There is no point in duplicating all that complexity.
*/
static void mpage_read_end_io(struct bio *bio)
{
struct folio_iter fi;
int err = blk_status_to_errno(bio->bi_status);
bio_for_each_folio_all(fi, bio)
folio_end_read(fi.folio, err == 0);
bio_put(bio);
}
static void mpage_write_end_io(struct bio *bio)
{
struct folio_iter fi;
int err = blk_status_to_errno(bio->bi_status);
bio_for_each_folio_all(fi, bio) {
if (err)
mapping_set_error(fi.folio->mapping, err);
folio_end_writeback(fi.folio);
}
bio_put(bio);
}
static struct bio *mpage_bio_submit_read(struct bio *bio)
{
bio->bi_end_io = mpage_read_end_io;
guard_bio_eod(bio);
submit_bio(bio);
return NULL;
}
static struct bio *mpage_bio_submit_write(struct bio *bio)
{
bio->bi_end_io = mpage_write_end_io;
guard_bio_eod(bio);
submit_bio(bio);
return NULL;
}
/*
* support function for mpage_readahead. The fs supplied get_block might
* return an up to date buffer. This is used to map that buffer into
* the page, which allows read_folio to avoid triggering a duplicate call
* to get_block.
*
* The idea is to avoid adding buffers to pages that don't already have
* them. So when the buffer is up to date and the page size == block size,
* this marks the page up to date instead of adding new buffers.
*/
static void map_buffer_to_folio(struct folio *folio, struct buffer_head *bh,
int page_block)
{
struct inode *inode = folio->mapping->host;
struct buffer_head *page_bh, *head;
int block = 0;
head = folio_buffers(folio);
if (!head) {
/*
* don't make any buffers if there is only one buffer on
* the folio and the folio just needs to be set up to date
*/
if (inode->i_blkbits == PAGE_SHIFT &&
buffer_uptodate(bh)) {
folio_mark_uptodate(folio);
return;
}
head = create_empty_buffers(folio, i_blocksize(inode), 0);
}
page_bh = head;
do {
if (block == page_block) {
page_bh->b_state = bh->b_state;
page_bh->b_bdev = bh->b_bdev;
page_bh->b_blocknr = bh->b_blocknr;
break;
}
page_bh = page_bh->b_this_page;
block++;
} while (page_bh != head);
}
struct mpage_readpage_args {
struct bio *bio;
struct folio *folio;
unsigned int nr_pages;
bool is_readahead;
sector_t last_block_in_bio;
struct buffer_head map_bh;
unsigned long first_logical_block;
get_block_t *get_block;
};
/*
* This is the worker routine which does all the work of mapping the disk
* blocks and constructs largest possible bios, submits them for IO if the
* blocks are not contiguous on the disk.
*
* We pass a buffer_head back and forth and use its buffer_mapped() flag to
* represent the validity of its disk mapping and to decide when to do the next
* get_block() call.
*/
static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
{
struct folio *folio = args->folio;
struct inode *inode = folio->mapping->host;
const unsigned blkbits = inode->i_blkbits;
const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
const unsigned blocksize = 1 << blkbits;
struct buffer_head *map_bh = &args->map_bh;
sector_t block_in_file;
sector_t last_block;
sector_t last_block_in_file;
sector_t first_block;
unsigned page_block;
unsigned first_hole = blocks_per_page;
struct block_device *bdev = NULL;
int length;
int fully_mapped = 1;
blk_opf_t opf = REQ_OP_READ;
unsigned nblocks;
unsigned relative_block;
gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
/* MAX_BUF_PER_PAGE, for example */
VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
if (args->is_readahead) {
opf |= REQ_RAHEAD;
gfp |= __GFP_NORETRY | __GFP_NOWARN;
}
if (folio_buffers(folio))
goto confused;
block_in_file = (sector_t)folio->index << (PAGE_SHIFT - blkbits);
last_block = block_in_file + args->nr_pages * blocks_per_page;
last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
if (last_block > last_block_in_file)
last_block = last_block_in_file;
page_block = 0;
/*
* Map blocks using the result from the previous get_blocks call first.
*/
nblocks = map_bh->b_size >> blkbits;
if (buffer_mapped(map_bh) &&
block_in_file > args->first_logical_block &&
block_in_file < (args->first_logical_block + nblocks)) {
unsigned map_offset = block_in_file - args->first_logical_block;
unsigned last = nblocks - map_offset;
first_block = map_bh->b_blocknr + map_offset;
for (relative_block = 0; ; relative_block++) {
if (relative_block == last) {
clear_buffer_mapped(map_bh);
break;
}
if (page_block == blocks_per_page)
break;
page_block++;
block_in_file++;
}
bdev = map_bh->b_bdev;
}
/*
* Then do more get_blocks calls until we are done with this folio.
*/
map_bh->b_folio = folio;
while (page_block < blocks_per_page) {
map_bh->b_state = 0;
map_bh->b_size = 0;
if (block_in_file < last_block) {
map_bh->b_size = (last_block-block_in_file) << blkbits;
if (args->get_block(inode, block_in_file, map_bh, 0))
goto confused;
args->first_logical_block = block_in_file;
}
if (!buffer_mapped(map_bh)) {
fully_mapped = 0;
if (first_hole == blocks_per_page)
first_hole = page_block;
page_block++;
block_in_file++;
continue;
}
/* some filesystems will copy data into the page during
* the get_block call, in which case we don't want to
* read it again. map_buffer_to_folio copies the data
* we just collected from get_block into the folio's buffers
* so read_folio doesn't have to repeat the get_block call
*/
if (buffer_uptodate(map_bh)) {
map_buffer_to_folio(folio, map_bh, page_block);
goto confused;
}
if (first_hole != blocks_per_page)
goto confused; /* hole -> non-hole */
/* Contiguous blocks? */
if (!page_block)
first_block = map_bh->b_blocknr;
else if (first_block + page_block != map_bh->b_blocknr)
goto confused;
nblocks = map_bh->b_size >> blkbits;
for (relative_block = 0; ; relative_block++) {
if (relative_block == nblocks) {
clear_buffer_mapped(map_bh);
break;
} else if (page_block == blocks_per_page)
break;
page_block++;
block_in_file++;
}
bdev = map_bh->b_bdev;
}
if (first_hole != blocks_per_page) {
folio_zero_segment(folio, first_hole << blkbits, PAGE_SIZE);
if (first_hole == 0) {
folio_mark_uptodate(folio);
folio_unlock(folio);
goto out;
}
} else if (fully_mapped) {
folio_set_mappedtodisk(folio);
}
/*
* This folio will go to BIO. Do we need to send this BIO off first?
*/
if (args->bio && (args->last_block_in_bio != first_block - 1))
args->bio = mpage_bio_submit_read(args->bio);
alloc_new:
if (args->bio == NULL) {
args->bio = bio_alloc(bdev, bio_max_segs(args->nr_pages), opf,
gfp);
if (args->bio == NULL)
goto confused;
args->bio->bi_iter.bi_sector = first_block << (blkbits - 9);
}
length = first_hole << blkbits;
if (!bio_add_folio(args->bio, folio, length, 0)) {
args->bio = mpage_bio_submit_read(args->bio);
goto alloc_new;
}
relative_block = block_in_file - args->first_logical_block;
nblocks = map_bh->b_size >> blkbits;
if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
(first_hole != blocks_per_page))
args->bio = mpage_bio_submit_read(args->bio);
else
args->last_block_in_bio = first_block + blocks_per_page - 1;
out:
return args->bio;
confused:
if (args->bio)
args->bio = mpage_bio_submit_read(args->bio);
if (!folio_test_uptodate(folio))
block_read_full_folio(folio, args->get_block);
else
folio_unlock(folio);
goto out;
}
/**
* mpage_readahead - start reads against pages
* @rac: Describes which pages to read.
* @get_block: The filesystem's block mapper function.
*
* This function walks the pages and the blocks within each page, building and
* emitting large BIOs.
*
* If anything unusual happens, such as:
*
* - encountering a page which has buffers
* - encountering a page which has a non-hole after a hole
* - encountering a page with non-contiguous blocks
*
* then this code just gives up and calls the buffer_head-based read function.
* It does handle a page which has holes at the end - that is a common case:
* the end-of-file on blocksize < PAGE_SIZE setups.
*
* BH_Boundary explanation:
*
* There is a problem. The mpage read code assembles several pages, gets all
* their disk mappings, and then submits them all. That's fine, but obtaining
* the disk mappings may require I/O. Reads of indirect blocks, for example.
*
* So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
* submitted in the following order:
*
* 12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
*
* because the indirect block has to be read to get the mappings of blocks
* 13,14,15,16. Obviously, this impacts performance.
*
* So what we do it to allow the filesystem's get_block() function to set
* BH_Boundary when it maps block 11. BH_Boundary says: mapping of the block
* after this one will require I/O against a block which is probably close to
* this one. So you should push what I/O you have currently accumulated.
*
* This all causes the disk requests to be issued in the correct order.
*/
void mpage_readahead(struct readahead_control *rac, get_block_t get_block)
{
struct folio *folio;
struct mpage_readpage_args args = {
.get_block = get_block,
.is_readahead = true,
};
while ((folio = readahead_folio(rac))) {
prefetchw(&folio->flags);
args.folio = folio;
args.nr_pages = readahead_count(rac);
args.bio = do_mpage_readpage(&args);
}
if (args.bio)
mpage_bio_submit_read(args.bio);
}
EXPORT_SYMBOL(mpage_readahead);
/*
* This isn't called much at all
*/
int mpage_read_folio(struct folio *folio, get_block_t get_block)
{
struct mpage_readpage_args args = {
.folio = folio,
.nr_pages = 1,
.get_block = get_block,
};
args.bio = do_mpage_readpage(&args);
if (args.bio)
mpage_bio_submit_read(args.bio);
return 0;
}
EXPORT_SYMBOL(mpage_read_folio);
/*
* Writing is not so simple.
*
* If the page has buffers then they will be used for obtaining the disk
* mapping. We only support pages which are fully mapped-and-dirty, with a
* special case for pages which are unmapped at the end: end-of-file.
*
* If the page has no buffers (preferred) then the page is mapped here.
*
* If all blocks are found to be contiguous then the page can go into the
* BIO. Otherwise fall back to the mapping's writepage().
*
* FIXME: This code wants an estimate of how many pages are still to be
* written, so it can intelligently allocate a suitably-sized BIO. For now,
* just allocate full-size (16-page) BIOs.
*/
struct mpage_data {
struct bio *bio;
sector_t last_block_in_bio;
get_block_t *get_block;
};
/*
* We have our BIO, so we can now mark the buffers clean. Make
* sure to only clean buffers which we know we'll be writing.
*/
static void clean_buffers(struct folio *folio, unsigned first_unmapped)
{
unsigned buffer_counter = 0;
struct buffer_head *bh, *head = folio_buffers(folio);
if (!head)
return;
bh = head;
do {
if (buffer_counter++ == first_unmapped)
break;
clear_buffer_dirty(bh);
bh = bh->b_this_page;
} while (bh != head);
/*
* we cannot drop the bh if the page is not uptodate or a concurrent
* read_folio would fail to serialize with the bh and it would read from
* disk before we reach the platter.
*/
if (buffer_heads_over_limit && folio_test_uptodate(folio))
try_to_free_buffers(folio);
}
static int __mpage_writepage(struct folio *folio, struct writeback_control *wbc,
void *data)
{
struct mpage_data *mpd = data;
struct bio *bio = mpd->bio;
struct address_space *mapping = folio->mapping;
struct inode *inode = mapping->host;
const unsigned blkbits = inode->i_blkbits;
const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
sector_t last_block;
sector_t block_in_file;
sector_t first_block;
unsigned page_block;
unsigned first_unmapped = blocks_per_page;
struct block_device *bdev = NULL;
int boundary = 0;
sector_t boundary_block = 0;
struct block_device *boundary_bdev = NULL;
size_t length;
struct buffer_head map_bh;
loff_t i_size = i_size_read(inode);
int ret = 0;
struct buffer_head *head = folio_buffers(folio);
if (head) {
struct buffer_head *bh = head;
/* If they're all mapped and dirty, do it */
page_block = 0;
do {
BUG_ON(buffer_locked(bh));
if (!buffer_mapped(bh)) {
/*
* unmapped dirty buffers are created by
* block_dirty_folio -> mmapped data
*/
if (buffer_dirty(bh))
goto confused;
if (first_unmapped == blocks_per_page)
first_unmapped = page_block;
continue;
}
if (first_unmapped != blocks_per_page)
goto confused; /* hole -> non-hole */
if (!buffer_dirty(bh) || !buffer_uptodate(bh))
goto confused;
if (page_block) {
if (bh->b_blocknr != first_block + page_block)
goto confused;
} else {
first_block = bh->b_blocknr;
}
page_block++;
boundary = buffer_boundary(bh);
if (boundary) {
boundary_block = bh->b_blocknr;
boundary_bdev = bh->b_bdev;
}
bdev = bh->b_bdev;
} while ((bh = bh->b_this_page) != head);
if (first_unmapped)
goto page_is_mapped;
/*
* Page has buffers, but they are all unmapped. The page was
* created by pagein or read over a hole which was handled by
* block_read_full_folio(). If this address_space is also
* using mpage_readahead then this can rarely happen.
*/
goto confused;
}
/*
* The page has no buffers: map it to disk
*/
BUG_ON(!folio_test_uptodate(folio));
block_in_file = (sector_t)folio->index << (PAGE_SHIFT - blkbits);
/*
* Whole page beyond EOF? Skip allocating blocks to avoid leaking
* space.
*/
if (block_in_file >= (i_size + (1 << blkbits) - 1) >> blkbits)
goto page_is_mapped;
last_block = (i_size - 1) >> blkbits;
map_bh.b_folio = folio;
for (page_block = 0; page_block < blocks_per_page; ) {
map_bh.b_state = 0;
map_bh.b_size = 1 << blkbits;
if (mpd->get_block(inode, block_in_file, &map_bh, 1))
goto confused;
if (!buffer_mapped(&map_bh))
goto confused;
if (buffer_new(&map_bh))
clean_bdev_bh_alias(&map_bh);
if (buffer_boundary(&map_bh)) {
boundary_block = map_bh.b_blocknr;
boundary_bdev = map_bh.b_bdev;
}
if (page_block) {
if (map_bh.b_blocknr != first_block + page_block)
goto confused;
} else {
first_block = map_bh.b_blocknr;
}
page_block++;
boundary = buffer_boundary(&map_bh);
bdev = map_bh.b_bdev;
if (block_in_file == last_block)
break;
block_in_file++;
}
BUG_ON(page_block == 0);
first_unmapped = page_block;
page_is_mapped:
/* Don't bother writing beyond EOF, truncate will discard the folio */
if (folio_pos(folio) >= i_size)
goto confused;
length = folio_size(folio);
if (folio_pos(folio) + length > i_size) {
/*
* The page straddles i_size. It must be zeroed out on each
* and every writepage invocation because it may be mmapped.
* "A file is mapped in multiples of the page size. For a file
* that is not a multiple of the page size, the remaining memory
* is zeroed when mapped, and writes to that region are not
* written out to the file."
*/
length = i_size - folio_pos(folio);
folio_zero_segment(folio, length, folio_size(folio));
}
/*
* This page will go to BIO. Do we need to send this BIO off first?
*/
if (bio && mpd->last_block_in_bio != first_block - 1)
bio = mpage_bio_submit_write(bio);
alloc_new:
if (bio == NULL) {
bio = bio_alloc(bdev, BIO_MAX_VECS,
REQ_OP_WRITE | wbc_to_write_flags(wbc),
GFP_NOFS);
bio->bi_iter.bi_sector = first_block << (blkbits - 9);
wbc_init_bio(wbc, bio);
bio->bi_write_hint = inode->i_write_hint;
}
/*
* Must try to add the page before marking the buffer clean or
* the confused fail path above (OOM) will be very confused when
* it finds all bh marked clean (i.e. it will not write anything)
*/
wbc_account_cgroup_owner(wbc, &folio->page, folio_size(folio));
length = first_unmapped << blkbits;
if (!bio_add_folio(bio, folio, length, 0)) {
bio = mpage_bio_submit_write(bio);
goto alloc_new;
}
clean_buffers(folio, first_unmapped);
BUG_ON(folio_test_writeback(folio));
folio_start_writeback(folio);
folio_unlock(folio);
if (boundary || (first_unmapped != blocks_per_page)) {
bio = mpage_bio_submit_write(bio);
if (boundary_block) {
write_boundary_block(boundary_bdev,
boundary_block, 1 << blkbits);
}
} else {
mpd->last_block_in_bio = first_block + blocks_per_page - 1;
}
goto out;
confused:
if (bio)
bio = mpage_bio_submit_write(bio);
/*
* The caller has a ref on the inode, so *mapping is stable
*/
ret = block_write_full_folio(folio, wbc, mpd->get_block);
mapping_set_error(mapping, ret);
out:
mpd->bio = bio;
return ret;
}
/**
* mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
* @mapping: address space structure to write
* @wbc: subtract the number of written pages from *@wbc->nr_to_write
* @get_block: the filesystem's block mapper function.
*
* This is a library function, which implements the writepages()
* address_space_operation.
*/
int
mpage_writepages(struct address_space *mapping,
struct writeback_control *wbc, get_block_t get_block)
{
struct mpage_data mpd = {
.get_block = get_block,
};
struct blk_plug plug;
int ret;
blk_start_plug(&plug);
ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
if (mpd.bio)
mpage_bio_submit_write(mpd.bio);
blk_finish_plug(&plug);
return ret;
}
EXPORT_SYMBOL(mpage_writepages);
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