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Date: Thu, 11 Jun 2020 10:12:45 +0800 From: "zhangyi (F)" <yi.zhang@...wei.com> To: Jan Kara <jack@...e.cz>, "Theodore Y. Ts'o" <tytso@....edu> CC: <linux-ext4@...r.kernel.org>, <adilger.kernel@...ger.ca>, <zhangxiaoxu5@...wei.com> Subject: Re: [PATCH 00/10] ext4: fix inconsistency since reading old metadata from disk On 2020/6/11 0:27, Jan Kara wrote: > On Wed 10-06-20 11:45:43, Theodore Y. Ts'o wrote: >> On Wed, Jun 10, 2020 at 11:57:39AM +0200, Jan Kara wrote: >>>> So I guess it may still lead to inconsistency. How about add this checking >>>> into ext4_journal_get_write_access() ? >>> >>> Yes, this also occured to me later. Adding the check to >>> ext4_journal_get_write_access() should be safer. >> >> There's another thing which we could do. One of the issues is that we >> allow buffered writeback for block devices once the change to the >> block has been committed. What if we add a change to block device >> writeback code and in fs/buffer.c so that optionally, the file system >> can specify a callback function can get called when an I/O error has >> been reflected back up from the block layer? >> >> It seems unfortunate that currently, we can immediately report the I/O >> error for buffered writes to *files*, but for metadata blocks, we >> would only be able to report the problem when we next try to modify >> it. >> >> Making changes to fs/buffer.c might be controversial, but I think it >> might be result in a better solution. > > Yeah, what you propose certainly makes sence could be relatively easily > done by blkdev_writepage() using __block_write_full_page() with appropriate > endio handler which calls fs callback. I'm just not sure how propagate the > callback function from the fs to the blkdev... > I have thought about this solution, we could add a hook in 'struct super_operations' and call it in blkdev_writepage() like blkdev_releasepage() does, and pick out a wrapper from block_write_full_page() to pass our endio handler in, something like this. static const struct super_operations ext4_sops = { ... .bdev_write_page = ext4_bdev_write_page, ... }; static int blkdev_writepage(struct page *page, struct writeback_control *wbc) { struct super_block *super = BDEV_I(page->mapping->host)->bdev.bd_super; if (super && super->s_op->bdev_write_page) return super->s_op->bdev_write_page(page, blkdev_get_block, wbc); return block_write_full_page(page, blkdev_get_block, wbc); } But I'm not sure it's a optimal ieda. So I continue to realize the "wb_err" solution now ? Thanks, Yi.
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