- A+
int ext4_mpage_readpages(struct address_space *mapping, struct list_head *pages, struct page *page, unsigned nr_pages) { struct bio *bio = NULL; unsigned page_idx; sector_t last_block_in_bio = 0; struct inode *inode = mapping->host; const unsigned blkbits = inode->i_blkbits; const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits; const unsigned blocksize = 1 << blkbits; 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; struct block_device *bdev = inode->i_sb->s_bdev; int length; unsigned relative_block = 0; struct ext4_map_blocks map; map.m_pblk = 0; map.m_lblk = 0; map.m_len = 0; map.m_flags = 0; for (page_idx = 0; nr_pages; page_idx++, nr_pages--) { int fully_mapped = 1; unsigned first_hole = blocks_per_page; prefetchw(&page->flags); if (pages) { page = list_entry(pages->prev, struct page, lru); list_del(&page->lru); if (add_to_page_cache_lru(page, mapping, page->index, mapping_gfp_constraint(mapping, GFP_KERNEL))) goto next_page; } if (page_has_buffers(page)) goto confused; block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits); last_block = block_in_file + 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 previous result first. */ if ((map.m_flags & EXT4_MAP_MAPPED) && block_in_file > map.m_lblk && block_in_file < (map.m_lblk + map.m_len)) { unsigned map_offset = block_in_file - map.m_lblk; unsigned last = map.m_len - map_offset; for (relative_block = 0; ; relative_block++) { if (relative_block == last) { /* needed? */ map.m_flags &= ~EXT4_MAP_MAPPED; break; } if (page_block == blocks_per_page) break; blocks[page_block] = map.m_pblk + map_offset + relative_block; page_block++; block_in_file++; } } /* * Then do more ext4_map_blocks() calls until we are * done with this page. */ while (page_block < blocks_per_page) { if (block_in_file < last_block) { map.m_lblk = block_in_file; map.m_len = last_block - block_in_file; if (ext4_map_blocks(NULL, inode, &map, 0) < 0) { set_error_page: SetPageError(page); zero_user_segment(page, 0, PAGE_CACHE_SIZE); unlock_page(page); goto next_page; } } if ((map.m_flags & EXT4_MAP_MAPPED) == 0) { fully_mapped = 0; if (first_hole == blocks_per_page) first_hole = page_block; page_block++; block_in_file++; continue; } if (first_hole != blocks_per_page) goto confused; /* hole -> non-hole */ /* Contiguous blocks? */ if (page_block && blocks[page_block-1] != map.m_pblk-1) goto confused; for (relative_block = 0; ; relative_block++) { if (relative_block == map.m_len) { /* needed? */ map.m_flags &= ~EXT4_MAP_MAPPED; break; } else if (page_block == blocks_per_page) break; blocks[page_block] = map.m_pblk+relative_block; page_block++; block_in_file++; } } if (first_hole != blocks_per_page) { zero_user_segment(page, first_hole << blkbits, PAGE_CACHE_SIZE); if (first_hole == 0) { SetPageUptodate(page); unlock_page(page); goto next_page; } } 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 (bio && (last_block_in_bio != blocks[0] - 1)) { submit_and_realloc: ext4_submit_bio_read(bio); bio = NULL; } if (bio == NULL) { struct ext4_crypto_ctx *ctx = NULL; if (ext4_encrypted_inode(inode) && S_ISREG(inode->i_mode)) { ctx = ext4_get_crypto_ctx(inode); if (IS_ERR(ctx)) goto set_error_page; } bio = bio_alloc(GFP_KERNEL, min_t(int, nr_pages, BIO_MAX_PAGES)); if (!bio) { if (ctx) ext4_release_crypto_ctx(ctx); goto set_error_page; } bio->bi_bdev = bdev; bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9); bio->bi_end_io = mpage_end_io; bio->bi_private = ctx; } length = first_hole << blkbits; if (bio_add_page(bio, page, length, 0) < length) goto submit_and_realloc; if (((map.m_flags & EXT4_MAP_BOUNDARY) && (relative_block == map.m_len)) || (first_hole != blocks_per_page)) { ext4_submit_bio_read(bio); bio = NULL; } else last_block_in_bio = blocks[blocks_per_page - 1]; goto next_page; confused: if (bio) { ext4_submit_bio_read(bio); bio = NULL; } if (!PageUptodate(page)) block_read_full_page(page, ext4_get_block); else unlock_page(page); next_page: if (pages) page_cache_release(page); } BUG_ON(pages && !list_empty(pages)); if (bio) ext4_submit_bio_read(bio); return 0; } int bio_add_page(struct bio *bio, struct page *page, unsigned int len, unsigned int offset) { struct bio_vec *bv; /* * cloned bio must not modify vec list */ if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED))) return 0; /* * For filesystems with a blocksize smaller than the pagesize * we will often be called with the same page as last time and * a consecutive offset. Optimize this special case. */ if (bio->bi_vcnt > 0) { bv = &bio->bi_io_vec[bio->bi_vcnt - 1]; if (page == bv->bv_page && offset == bv->bv_offset + bv->bv_len) { bv->bv_len += len; goto done; } } if (bio->bi_vcnt >= bio->bi_max_vecs) return 0; bv = &bio->bi_io_vec[bio->bi_vcnt]; bv->bv_page = page; bv->bv_len = len; bv->bv_offset = offset; bio->bi_vcnt++; done: bio->bi_iter.bi_size += len; return len; } // sumbit (bio) /****************************************驱动程序****************************************************************/ getbio(); struct bio_vec* bvec; pRHdata = pdev->data + (bio->bi_sector * RAMHD_SECTOR_SIZE); bio_for_each_segment(bvec, bio, i){ pBuffer = kmap(bvec->bv_page) + bvec->bv_offset; switch(bio_data_dir(bio)){ case READ: memcpy(pBuffer, pRHdata, bvec->bv_len); flush_dcache_page(bvec->bv_page); break; case WRITE: flush_dcache_page(bvec->bv_page); memcpy(pRHdata, pBuffer, bvec->bv_len); break; default: kunmap(bvec->bv_page); goto out; } kunmap(bvec->bv_page); pRHdata += bvec->bv_len; }
- 首先是疑问,就是在准备探索cfq和红黑树的时候,知道红黑树应该是根据磁盘的bi_sector进行树的组织的,那么这个bi_setctor是哪里来的,
- 第二个疑问:然后之前也一直疑问bio,应该是好几个page组成的,之前没有看到,所以就用单个bio去探索也不影响分析代码,今天顺便一起看下
第一问解答:
从上面代码就知道了,第一个标黑体的地方和第二个标记黑体的地方就是bi_setctor的由来
const unsigned blkbits = inode->i_blkbits;
bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
虽然还有些模糊,比如blkbits 是inode节点,相当于节点编号,相当于硬盘位置,但是这个iNode的又是最终是怎么来的呢?还需要探索。
还有减去9,还有blocks 左移是什么意思。
第二问解答:
bio_alloc
bio_add_page
如果bio还是空的,就用bio_alloc开辟一个,然后后面的page用bio_add_page,
然后在bio_add_page函数中我们对比bvec的小节点的数据流动,很清楚的看到,每个page的数据指针进行的数据传递,其实是个数组,并没有组织成链表。
# Linux必备书籍推荐
《LINUX内核源代码情景分析(上册) 》毛德操,胡希明 >>>京东购买 >>>淘宝购买
《LINUX内核源代码情景分析(下册) 》毛德操,胡希明 >>>京东购买 >>>淘宝购买
《嵌入式Linux应用开发完全手册 》韦东山 著 >>>京东购买 >>>淘宝购买 (领券)
《深入理解Linux内核第3版》(美)博韦 >>>京东购买 >>>淘宝购买
《鸟哥的Linux私房菜:基础学习篇(第四版)》鸟哥 >>>京东购买 >>>淘宝购买

扫一扫关注微信公众号,上述5本电子书免费领取。
https://pan.baidu.com/s/1q5IjXAmybs8NBseR4R8Ksg
扫码关注微信公众号,回复“Linux” ,即可获取提取码
--- Linux文件系统学习系列笔记 ---
(原创笔记,转载请联系博主授权)
Linux文件系统学习:io的plug过程-request请求(9)
Linux文件系统学习:io的plug过程-blk_init_queue(10)
Linux文件系统学习:io的plug过程-blk_flush_plug_list的情况(11)
Linux文件系统学习:io的plug过程-queuelist的问题(12)
<欢迎关注微信公众号,第一时间查看最新内容>
您可以选择一种方式赞助本站
支付宝扫一扫赞助
微信钱包扫描赞助
赏