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Wong" , Linus Torvalds , Amir Goldstein , Alexander Viro , Jaegeuk Kim , Theodore Ts'o , Pavel Machek , David Sterba , Li Guifu , Fang Wei , Greg Kroah-Hartman , linux-fsdevel@vger.kernel.org, Andrew Morton , linux-erofs@lists.ozlabs.org Subject: Re: [PATCH v6 03/24] erofs: add super block operations Message-ID: <20190902125109.GA9826@infradead.org> References: <20190802125347.166018-1-gaoxiang25@huawei.com> <20190802125347.166018-4-gaoxiang25@huawei.com> <20190829101545.GC20598@infradead.org> <20190901085452.GA4663@hsiangkao-HP-ZHAN-66-Pro-G1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190901085452.GA4663@hsiangkao-HP-ZHAN-66-Pro-G1> User-Agent: Mutt/1.11.4 (2019-03-13) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Sep 01, 2019 at 04:54:55PM +0800, Gao Xiang wrote: > No modification at this... (some comments already right here...) > 20 /* 128-byte erofs on-disk super block */ > 21 struct erofs_super_block { > ... > 24 __le32 features; /* (aka. feature_compat) */ > ... > 38 __le32 requirements; /* (aka. feature_incompat) */ > ... > 41 }; This is only cosmetic, why not stick to feature_compat and feature_incompat? > > > + bh = sb_bread(sb, 0); > > > > Is there any good reasons to use buffer heads like this in new code > > vs directly using bios? > > As you said, I want it in the page cache. > > The reason "why not use read_mapping_page or similar?" is simply > read_mapping_page -> .readpage -> (for bdev inode) block_read_full_page > -> create_page_buffers anyway... > > sb_bread haven't obsoleted... It has similar function though... With the different that it keeps you isolated from the buffer_head internals. This seems to be your only direct use of buffer heads, which while not deprecated are a bit of an ugly step child. So if you can easily avoid creating a buffer_head dependency in a new filesystem I think you should avoid it. > > > + sbi->build_time = le64_to_cpu(layout->build_time); > > > + sbi->build_time_nsec = le32_to_cpu(layout->build_time_nsec); > > > + > > > + memcpy(&sb->s_uuid, layout->uuid, sizeof(layout->uuid)); > > > + memcpy(sbi->volume_name, layout->volume_name, > > > + sizeof(layout->volume_name)); > > > > s_uuid should preferably be a uuid_t (assuming it is a real BE uuid, > > if it is le it should be a guid_t). > > For this case, I have no idea how to deal with... > I have little knowledge about this uuid stuff, so I just copied > from f2fs... (Could be no urgent of this field...) Who fills out this field in the on-disk format and how? > The background is Al's comments in erofs v2.... > (which simplify erofs_fill_super logic) > https://lore.kernel.org/r/20190720224955.GD17978@ZenIV.linux.org.uk/ > > with a specific notation... > https://lore.kernel.org/r/20190721040547.GF17978@ZenIV.linux.org.uk/ > > " > > OTOH, for the case of NULL ->s_root ->put_super() won't be called > > at all, so in that case you need it directly in ->kill_sb(). > " Yes. Although none of that is relevant for this initial version, just after more features are added.