// 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 axboe@suse.de * 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 <linux/cleancache.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_page(). * * 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_end_io(struct bio *bio){ struct bio_vec *bv; struct bvec_iter_all iter_all; bio_for_each_segment_all(bv, bio, iter_all) { struct page *page = bv->bv_page; page_endio(page, bio_op(bio), blk_status_to_errno(bio->bi_status)); } bio_put(bio);} static struct bio *mpage_bio_submit(int op, int op_flags, struct bio *bio){ bio->bi_end_io = mpage_end_io; bio_set_op_attrs(bio, op, op_flags); guard_bio_eod(bio); submit_bio(bio); return NULL;} static struct bio *mpage_alloc(struct block_device *bdev, sector_t first_sector, int nr_vecs, gfp_t gfp_flags){ struct bio *bio; /* Restrict the given (page cache) mask for slab allocations */ gfp_flags &= GFP_KERNEL; bio = bio_alloc(gfp_flags, nr_vecs); if (bio == NULL && (current->flags & PF_MEMALLOC)) { while (!bio && (nr_vecs /= 2)) bio = bio_alloc(gfp_flags, nr_vecs); } if (bio) { bio_set_dev(bio, bdev); bio->bi_iter.bi_sector = first_sector; } return bio;} /* * 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 readpage 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_page(struct page *page, struct buffer_head *bh, int page_block) { struct inode *inode = page->mapping->host; struct buffer_head *page_bh, *head; int block = 0; if (!page_has_buffers(page)) { /* * don't make any buffers if there is only one buffer on * the page and the page just needs to be set up to date */ if (inode->i_blkbits == PAGE_SHIFT && buffer_uptodate(bh)) { SetPageUptodate(page); return; } create_empty_buffers(page, i_blocksize(inode), 0); } head = page_buffers(page); 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 page *page; 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 page *page = args->page; struct inode *inode = page->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 blocks[MAX_BUF_PER_PAGE]; unsigned page_block; unsigned first_hole = blocks_per_page; struct block_device *bdev = NULL; int length; int fully_mapped = 1; int op_flags; unsigned nblocks; unsigned relative_block; gfp_t gfp; if (args->is_readahead) { op_flags = REQ_RAHEAD; gfp = readahead_gfp_mask(page->mapping); } else { op_flags = 0; gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL); } if (page_has_buffers(page)) goto confused; block_in_file = (sector_t)page->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; for (relative_block = 0; ; relative_block++) { if (relative_block == last) { clear_buffer_mapped(map_bh); break; } if (page_block == blocks_per_page) break; blocks[page_block] = map_bh->b_blocknr + map_offset + relative_block; page_block++; block_in_file++; } bdev = map_bh->b_bdev; } /* * Then do more get_blocks calls until we are done with this page. */ map_bh->b_page = page; 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_page copies the data * we just collected from get_block into the page's buffers * so readpage doesn't have to repeat the get_block call */ if (buffer_uptodate(map_bh)) { map_buffer_to_page(page, map_bh, page_block); goto confused; } if (first_hole != blocks_per_page) goto confused; /* hole -> non-hole */ /* Contiguous blocks? */ if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1) 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; blocks[page_block] = map_bh->b_blocknr+relative_block; page_block++; block_in_file++; } bdev = map_bh->b_bdev; } if (first_hole != blocks_per_page) { zero_user_segment(page, first_hole << blkbits, PAGE_SIZE); if (first_hole == 0) { SetPageUptodate(page); unlock_page(page); goto out; } } else if (fully_mapped) { SetPageMappedToDisk(page); } if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) && cleancache_get_page(page) == 0) { SetPageUptodate(page); goto confused; } /* * This page will go to BIO. Do we need to send this BIO off first? */ if (args->bio && (args->last_block_in_bio != blocks[0] - 1)) args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio); alloc_new: if (args->bio == NULL) { if (first_hole == blocks_per_page) { if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9), page)) goto out; } args->bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9), bio_max_segs(args->nr_pages), gfp); if (args->bio == NULL) goto confused; } length = first_hole << blkbits; if (bio_add_page(args->bio, page, length, 0) < length) { args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, 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(REQ_OP_READ, op_flags, args->bio); else args->last_block_in_bio = blocks[blocks_per_page - 1];out: return args->bio; confused: if (args->bio) args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio); if (!PageUptodate(page)) block_read_full_page(page, args->get_block); else unlock_page(page); 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 page *page; struct mpage_readpage_args args = { .get_block = get_block, .is_readahead = true, }; while ((page = readahead_page(rac))) { prefetchw(&page->flags); args.page = page; args.nr_pages = readahead_count(rac); args.bio = do_mpage_readpage(&args); put_page(page); } if (args.bio) mpage_bio_submit(REQ_OP_READ, REQ_RAHEAD, args.bio);}EXPORT_SYMBOL(mpage_readahead); /* * This isn't called much at all */int mpage_readpage(struct page *page, get_block_t get_block){ struct mpage_readpage_args args = { .page = page, .nr_pages = 1, .get_block = get_block, }; args.bio = do_mpage_readpage(&args); if (args.bio) mpage_bio_submit(REQ_OP_READ, 0, args.bio); return 0;}EXPORT_SYMBOL(mpage_readpage); /* * 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; unsigned use_writepage;}; /* * 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 page *page, unsigned first_unmapped){ unsigned buffer_counter = 0; struct buffer_head *bh, *head; if (!page_has_buffers(page)) return; head = page_buffers(page); 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 * readpage would fail to serialize with the bh and it would read from * disk before we reach the platter. */ if (buffer_heads_over_limit && PageUptodate(page)) try_to_free_buffers(page);} /* * For situations where we want to clean all buffers attached to a page. * We don't need to calculate how many buffers are attached to the page, * we just need to specify a number larger than the maximum number of buffers. */void clean_page_buffers(struct page *page){ clean_buffers(page, ~0U);} static int __mpage_writepage(struct page *page, struct writeback_control *wbc, void *data){ struct mpage_data *mpd = data; struct bio *bio = mpd->bio; struct address_space *mapping = page->mapping; struct inode *inode = page->mapping->host; const unsigned blkbits = inode->i_blkbits; unsigned long end_index; const unsigned blocks_per_page = PAGE_SIZE >> blkbits; sector_t last_block; sector_t block_in_file; sector_t blocks[MAX_BUF_PER_PAGE]; 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; int length; struct buffer_head map_bh; loff_t i_size = i_size_read(inode); int ret = 0;Lines 1–500 of 741. 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// 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 axboe@suse.de * 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 <linux/cleancache.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_page(). * * 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_end_io(struct bio *bio) { struct bio_vec *bv; struct bvec_iter_all iter_all; bio_for_each_segment_all(bv, bio, iter_all) { struct page *page = bv->bv_page; page_endio(page, bio_op(bio), blk_status_to_errno(bio->bi_status)); } bio_put(bio); } static struct bio *mpage_bio_submit(int op, int op_flags, struct bio *bio) { bio->bi_end_io = mpage_end_io; bio_set_op_attrs(bio, op, op_flags); guard_bio_eod(bio); submit_bio(bio); return NULL; } static struct bio * mpage_alloc(struct block_device *bdev, sector_t first_sector, int nr_vecs, gfp_t gfp_flags) { struct bio *bio; /* Restrict the given (page cache) mask for slab allocations */ gfp_flags &= GFP_KERNEL; bio = bio_alloc(gfp_flags, nr_vecs); if (bio == NULL && (current->flags & PF_MEMALLOC)) { while (!bio && (nr_vecs /= 2)) bio = bio_alloc(gfp_flags, nr_vecs); } if (bio) { bio_set_dev(bio, bdev); bio->bi_iter.bi_sector = first_sector; } return bio; } /* * 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 readpage 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_page(struct page *page, struct buffer_head *bh, int page_block) { struct inode *inode = page->mapping->host; struct buffer_head *page_bh, *head; int block = 0; if (!page_has_buffers(page)) { /* * don't make any buffers if there is only one buffer on * the page and the page just needs to be set up to date */ if (inode->i_blkbits == PAGE_SHIFT && buffer_uptodate(bh)) { SetPageUptodate(page); return; } create_empty_buffers(page, i_blocksize(inode), 0); } head = page_buffers(page); 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 page *page; 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 page *page = args->page; struct inode *inode = page->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 blocks[MAX_BUF_PER_PAGE]; unsigned page_block; unsigned first_hole = blocks_per_page; struct block_device *bdev = NULL; int length; int fully_mapped = 1; int op_flags; unsigned nblocks; unsigned relative_block; gfp_t gfp; if (args->is_readahead) { op_flags = REQ_RAHEAD; gfp = readahead_gfp_mask(page->mapping); } else { op_flags = 0; gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL); } if (page_has_buffers(page)) goto confused; block_in_file = (sector_t)page->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; for (relative_block = 0; ; relative_block++) { if (relative_block == last) { clear_buffer_mapped(map_bh); break; } if (page_block == blocks_per_page) break; blocks[page_block] = map_bh->b_blocknr + map_offset + relative_block; page_block++; block_in_file++; } bdev = map_bh->b_bdev; } /* * Then do more get_blocks calls until we are done with this page. */ map_bh->b_page = page; 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_page copies the data * we just collected from get_block into the page's buffers * so readpage doesn't have to repeat the get_block call */ if (buffer_uptodate(map_bh)) { map_buffer_to_page(page, map_bh, page_block); goto confused; } if (first_hole != blocks_per_page) goto confused; /* hole -> non-hole */ /* Contiguous blocks? */ if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1) 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; blocks[page_block] = map_bh->b_blocknr+relative_block; page_block++; block_in_file++; } bdev = map_bh->b_bdev; } if (first_hole != blocks_per_page) { zero_user_segment(page, first_hole << blkbits, PAGE_SIZE); if (first_hole == 0) { SetPageUptodate(page); unlock_page(page); goto out; } } else if (fully_mapped) { SetPageMappedToDisk(page); } if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) && cleancache_get_page(page) == 0) { SetPageUptodate(page); goto confused; } /* * This page will go to BIO. Do we need to send this BIO off first? */ if (args->bio && (args->last_block_in_bio != blocks[0] - 1)) args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio); alloc_new: if (args->bio == NULL) { if (first_hole == blocks_per_page) { if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9), page)) goto out; } args->bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9), bio_max_segs(args->nr_pages), gfp); if (args->bio == NULL) goto confused; } length = first_hole << blkbits; if (bio_add_page(args->bio, page, length, 0) < length) { args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, 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(REQ_OP_READ, op_flags, args->bio); else args->last_block_in_bio = blocks[blocks_per_page - 1]; out: return args->bio; confused: if (args->bio) args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio); if (!PageUptodate(page)) block_read_full_page(page, args->get_block); else unlock_page(page); 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 page *page; struct mpage_readpage_args args = { .get_block = get_block, .is_readahead = true, }; while ((page = readahead_page(rac))) { prefetchw(&page->flags); args.page = page; args.nr_pages = readahead_count(rac); args.bio = do_mpage_readpage(&args); put_page(page); } if (args.bio) mpage_bio_submit(REQ_OP_READ, REQ_RAHEAD, args.bio); } EXPORT_SYMBOL(mpage_readahead); /* * This isn't called much at all */ int mpage_readpage(struct page *page, get_block_t get_block) { struct mpage_readpage_args args = { .page = page, .nr_pages = 1, .get_block = get_block, }; args.bio = do_mpage_readpage(&args); if (args.bio) mpage_bio_submit(REQ_OP_READ, 0, args.bio); return 0; } EXPORT_SYMBOL(mpage_readpage); /* * 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; unsigned use_writepage; }; /* * 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 page *page, unsigned first_unmapped) { unsigned buffer_counter = 0; struct buffer_head *bh, *head; if (!page_has_buffers(page)) return; head = page_buffers(page); 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 * readpage would fail to serialize with the bh and it would read from * disk before we reach the platter. */ if (buffer_heads_over_limit && PageUptodate(page)) try_to_free_buffers(page); } /* * For situations where we want to clean all buffers attached to a page. * We don't need to calculate how many buffers are attached to the page, * we just need to specify a number larger than the maximum number of buffers. */ void clean_page_buffers(struct page *page) { clean_buffers(page, ~0U); } static int __mpage_writepage(struct page *page, struct writeback_control *wbc, void *data) { struct mpage_data *mpd = data; struct bio *bio = mpd->bio; struct address_space *mapping = page->mapping; struct inode *inode = page->mapping->host; const unsigned blkbits = inode->i_blkbits; unsigned long end_index; const unsigned blocks_per_page = PAGE_SIZE >> blkbits; sector_t last_block; sector_t block_in_file; sector_t blocks[MAX_BUF_PER_PAGE]; 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; int length; struct buffer_head map_bh; loff_t i_size = i_size_read(inode); int ret = 0;