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Date: Thu, 24 Oct 2019 10:23:54 +0900 From: Philippe Liard <pliard@...gle.com> To: phillip@...ashfs.org.uk Cc: linux-kernel@...r.kernel.org, groeck@...omium.org, pliard@...gle.com Subject: Re: [PATCH] squashfs: Migrate from ll_rw_block usage to BIO Thanks Cristoph for taking a look. I like the idea of simplifying this if possible. I think I understand your suggestion in principle but I'm not seeing a way to apply it here. Would it be possible for you to be a little more specific? Let me try to explain this below. My admittedly limited understanding is that using BIO indirectly requires buffer_head or an alternative including some synchronization mechanism at least. It's true that the bio_{alloc,add_page,submit}() functions don't require passing a buffer_head. However because bio_submit() is asynchronous AFAICT the client needs to use a synchronization mechanism to wait for and notify the completion of the request which buffer heads provide. This is achieved respectively by wait_on_buffer() and {set,clear}_buffer_uptodate(). Another dependency on buffer heads is the fact that squashfs_read_data() calls into other squashfs functions operating on buffer heads outside this file. For example squashfs_decompress() operates on a buffer_head array. Given that bio_submit() is asynchronous I'm also not seeing how the squashfs_bio_request allocation can be removed? There can be multiple BIO requests in flight each needing to carry some context used on completion of the request.
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