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*参照元 [#b0908ca0] #backlinks *説明 [#z8a74fb7] -パス: [[linux-2.6.33/fs/direct-io.c]] -FIXME: これは何？ --説明 **引数 [#ic1f3a23] -struct dio *dio -- --[[linux-2.6.33/dio]] **返り値 [#q51b1a39] -int -- **参考 [#pa3526bb] *実装 [#sd2d9661] /* * Walk the user pages, and the file, mapping blocks to disk and generating * a sequence of (page,offset,len,block) mappings. These mappings are injected * into submit_page_section(), which takes care of the next stage of submission * * Direct IO against a blockdev is different from a file. Because we can * happily perform page-sized but 512-byte aligned IOs. It is important that * blockdev IO be able to have fine alignment and large sizes. * * So what we do is to permit the ->get_block function to populate bh.b_size * with the size of IO which is permitted at this offset and this i_blkbits. * * For best results, the blockdev should be set up with 512-byte i_blkbits and * it should set b_size to PAGE_SIZE or more inside get_block(). This gives * fine alignment but still allows this function to work in PAGE_SIZE units. */ static int do_direct_IO(struct dio *dio) { const unsigned blkbits = dio->blkbits; const unsigned blocks_per_page = PAGE_SIZE >> blkbits; struct page *page; unsigned block_in_page; struct buffer_head *map_bh = &dio->map_bh; int ret = 0; - --[[linux-2.6.33/PAGE_SIZE]] --[[linux-2.6.33/page]] --[[linux-2.6.33/buffer_head]] /* The I/O can start at any block offset within the first page */ block_in_page = dio->first_block_in_page; while (dio->block_in_file < dio->final_block_in_request) { page = dio_get_page(dio); if (IS_ERR(page)) { ret = PTR_ERR(page); goto out; } - --[[linux-2.6.33/dio_get_page()]] --[[linux-2.6.33/IS_ERR()]] --[[linux-2.6.33/PTR_ERR()]] while (block_in_page < blocks_per_page) { unsigned offset_in_page = block_in_page << blkbits; unsigned this_chunk_bytes; /* # of bytes mapped */ unsigned this_chunk_blocks; /* # of blocks */ unsigned u; if (dio->blocks_available == 0) { /* * Need to go and map some more disk */ unsigned long blkmask; unsigned long dio_remainder; ret = get_more_blocks(dio); if (ret) { page_cache_release(page); goto out; } - --[[linux-2.6.33/get_more_blocks()]] --[[linux-2.6.33/page_cache_release()]] if (!buffer_mapped(map_bh)) goto do_holes; - --[[linux-2.6.33/buffer_mapped()]] dio->blocks_available = map_bh->b_size >> dio->blkbits; dio->next_block_for_io = map_bh->b_blocknr << dio->blkfactor; if (buffer_new(map_bh)) clean_blockdev_aliases(dio); - --[[linux-2.6.33/buffer_new()]] --[[linux-2.6.33/clean_blockdev_aliases()]] if (!dio->blkfactor) goto do_holes; blkmask = (1 << dio->blkfactor) - 1; dio_remainder = (dio->block_in_file & blkmask); /* * If we are at the start of IO and that IO * starts partway into a fs-block, * dio_remainder will be non-zero. If the IO * is a read then we can simply advance the IO * cursor to the first block which is to be * read. But if the IO is a write and the * block was newly allocated we cannot do that; * the start of the fs block must be zeroed out * on-disk */ if (!buffer_new(map_bh)) dio->next_block_for_io += dio_remainder; dio->blocks_available -= dio_remainder; } do_holes: /* Handle holes */ if (!buffer_mapped(map_bh)) { loff_t i_size_aligned; /* AKPM: eargh, -ENOTBLK is a hack */ if (dio->rw & WRITE) { page_cache_release(page); return -ENOTBLK; } /* * Be sure to account for a partial block as the * last block in the file */ i_size_aligned = ALIGN(i_size_read(dio->inode), 1 << blkbits); - --[[linux-2.6.33/ALIGN()]] --[[linux-2.6.33/i_size_read()]] if (dio->block_in_file >= i_size_aligned >> blkbits) { /* We hit eof */ page_cache_release(page); goto out; } zero_user(page, block_in_page << blkbits, 1 << blkbits); - --[[linux-2.6.33/zero_user()]] dio->block_in_file++; block_in_page++; goto next_block; } /* * If we're performing IO which has an alignment which * is finer than the underlying fs, go check to see if * we must zero out the start of this block. */ if (unlikely(dio->blkfactor && !dio->start_zero_done)) dio_zero_block(dio, 0); - --[[linux-2.6.33/unlikely()]] --[[linux-2.6.33/dio_zero_block()]] /* * Work out, in this_chunk_blocks, how much disk we * can add to this page */ this_chunk_blocks = dio->blocks_available; u = (PAGE_SIZE - offset_in_page) >> blkbits; if (this_chunk_blocks > u) this_chunk_blocks = u; u = dio->final_block_in_request - dio->block_in_file; if (this_chunk_blocks > u) this_chunk_blocks = u; this_chunk_bytes = this_chunk_blocks << blkbits; BUG_ON(this_chunk_bytes == 0); - --[[linux-2.6.33/BUG_ON()]] dio->boundary = buffer_boundary(map_bh); - --[[linux-2.6.33/buffer_boundary()]] ret = submit_page_section(dio, page, offset_in_page, this_chunk_bytes, dio->next_block_for_io); if (ret) { page_cache_release(page); goto out; } - --[[linux-2.6.33/submit_page_section()]] dio->next_block_for_io += this_chunk_blocks; dio->block_in_file += this_chunk_blocks; block_in_page += this_chunk_blocks; dio->blocks_available -= this_chunk_blocks; next_block: BUG_ON(dio->block_in_file > dio->final_block_in_request); if (dio->block_in_file == dio->final_block_in_request) break; } /* Drop the ref which was taken in get_user_pages() */ page_cache_release(page); block_in_page = 0; } out: return ret; } *コメント [#lc87a411]
