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From: Pavel Machek <pavel@denx.de>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jan Kara <jack@suse.cz>, Chao Yu <yuchao0@huawei.com>,
	Dave Chinner <david@fromorbit.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Miao Xie <miaoxie@huawei.com>,
	devel@driverdev.osuosl.org,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	"Darrick J . Wong" <darrick.wong@oracle.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Amir Goldstein <amir73il@gmail.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Jaegeuk Kim <jaegeuk@kernel.org>, Theodore Ts'o <tytso@mit.edu>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	David Sterba <dsterba@suse.cz>,
	Li Guifu <bluce.liguifu@huawei.com>,
	Fang Wei <fangwei1@huawei.com>, Pavel Machek <pavel@denx.de>,
	linux-fsdevel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-erofs@lists.ozlabs.org
Subject: Re: [PATCH v6 01/24] erofs: add on-disk layout
Date: Mon, 2 Sep 2019 10:40:20 +0200	[thread overview]
Message-ID: <20190902084020.GB19557@amd> (raw)
In-Reply-To: <20190829095954.GB20598@infradead.org>


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Hi!

> > +struct erofs_super_block {
> > +/*  0 */__le32 magic;           /* in the little endian */
> > +/*  4 */__le32 checksum;        /* crc32c(super_block) */
> > +/*  8 */__le32 features;        /* (aka. feature_compat) */
> > +/* 12 */__u8 blkszbits;         /* support block_size == PAGE_SIZE only */
> 
> Please remove all the byte offset comments.  That is something that can
> easily be checked with gdb or pahole.

I don't think I agree. gdb will tell you byte offsets _on one
architecture_. But filesystem is supposed to be portable between them. 

> > +/* 64 */__u8 volume_name[16];   /* volume name */
> > +/* 80 */__le32 requirements;    /* (aka. feature_incompat) */
> > +
> > +/* 84 */__u8 reserved2[44];
> > +} __packed;                     /* 128 bytes */
> 
> Please don't add __packed.  In this case I think you don't need it
> (but double check with pahole), but even if you would need it using
> proper padding fields and making sure all fields are naturally aligned
> will give you much better code generation on architectures that don't
> support native unaligned access.

This is on-disk structure, right?

drivers/staging/erofs/super.c:	struct erofs_super_block *layout;
drivers/staging/erofs/super.c:	layout = (struct erofs_super_block
*)((u8 *)bh->b_data

So __packed is right thing to do. If architecture accesses that
slowly, that's ungood, but different structures between architectures
would be really bad.

Best regards,
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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  parent reply	other threads:[~2019-09-02  8:40 UTC|newest]

Thread overview: 141+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-02 12:53 [PATCH v6 00/24] erofs: promote erofs from staging Gao Xiang
2019-08-02 12:53 ` [PATCH v6 01/24] erofs: add on-disk layout Gao Xiang
     [not found]   ` <20190829095954.GB20598@infradead.org>
2019-09-01  7:54     ` Gao Xiang
2019-09-02 12:45       ` Christoph Hellwig
2019-09-02 13:02         ` Gao Xiang
2019-09-02  8:40     ` Pavel Machek [this message]
2019-09-02 10:35       ` Gao Xiang
     [not found]     ` <20190829103252.GA64893@architecture4>
     [not found]       ` <67d6efbbc9ac6db23215660cb970b7ef29dc0c1d.camel@perches.com>
     [not found]         ` <20190830120714.GN2752@twin.jikos.cz>
2019-09-02  8:43           ` Pavel Machek
2019-09-02 14:07             ` David Sterba
2019-09-03 11:27               ` Pavel Machek
2019-08-02 12:53 ` [PATCH v6 02/24] erofs: add erofs in-memory stuffs Gao Xiang
2019-08-02 12:53 ` [PATCH v6 03/24] erofs: add super block operations Gao Xiang
     [not found]   ` <20190829101545.GC20598@infradead.org>
     [not found]     ` <20190829105048.GB64893@architecture4>
2019-08-30 16:39       ` Christoph Hellwig
2019-08-30 17:15         ` Gao Xiang
2019-08-31  0:54           ` Gao Xiang
2019-08-31  6:34           ` Amir Goldstein
2019-08-31  6:48             ` Gao Xiang
2019-09-01  8:54     ` Gao Xiang
2019-09-02 12:51       ` Christoph Hellwig
2019-09-02 14:43         ` Gao Xiang
2019-09-02 15:19           ` Christoph Hellwig
2019-09-02 15:24             ` Gao Xiang
2019-08-02 12:53 ` [PATCH v6 04/24] erofs: add raw address_space operations Gao Xiang
     [not found]   ` <20190829101721.GD20598@infradead.org>
     [not found]     ` <20190829114610.GF64893@architecture4>
2019-08-30 16:40       ` Christoph Hellwig
2019-08-30 17:23         ` Gao Xiang
2019-08-02 12:53 ` [PATCH v6 05/24] erofs: add inode operations Gao Xiang
     [not found]   ` <20190829102426.GE20598@infradead.org>
     [not found]     ` <20190829115922.GG64893@architecture4>
2019-08-30 16:42       ` Christoph Hellwig
2019-08-30 18:46         ` Gao Xiang
2019-09-01  9:34     ` Gao Xiang
2019-09-02 12:53       ` Christoph Hellwig
2019-09-02 13:43       ` David Sterba
2019-09-02 13:55         ` Gao Xiang
2019-08-02 12:53 ` [PATCH v6 06/24] erofs: support special inode Gao Xiang
     [not found]   ` <20190829102503.GF20598@infradead.org>
2019-09-01  9:39     ` Gao Xiang
2019-08-02 12:53 ` [PATCH v6 07/24] erofs: add directory operations Gao Xiang
2019-08-02 12:53 ` [PATCH v6 08/24] erofs: add namei functions Gao Xiang
2019-08-02 12:53 ` [PATCH v6 09/24] erofs: support tracepoint Gao Xiang
2019-08-02 12:53 ` [PATCH v6 10/24] erofs: update Kconfig and Makefile Gao Xiang
2019-08-02 12:53 ` [PATCH v6 11/24] erofs: introduce xattr & posixacl support Gao Xiang
2019-08-02 12:53 ` [PATCH v6 12/24] erofs: introduce tagged pointer Gao Xiang
2019-08-02 12:53 ` [PATCH v6 13/24] erofs: add compression indexes support Gao Xiang
2019-08-02 12:53 ` [PATCH v6 14/24] erofs: introduce superblock registration Gao Xiang
2019-08-02 12:53 ` [PATCH v6 15/24] erofs: introduce erofs shrinker Gao Xiang
2019-08-02 12:53 ` [PATCH v6 16/24] erofs: introduce workstation for decompression Gao Xiang
2019-08-02 12:53 ` [PATCH v6 17/24] erofs: introduce per-CPU buffers implementation Gao Xiang
2019-08-02 12:53 ` [PATCH v6 18/24] erofs: introduce pagevec for decompression subsystem Gao Xiang
2019-08-02 12:53 ` [PATCH v6 19/24] erofs: add erofs_allocpage() Gao Xiang
2019-08-02 12:53 ` [PATCH v6 20/24] erofs: introduce generic decompression backend Gao Xiang
2019-08-02 12:53 ` [PATCH v6 21/24] erofs: introduce LZ4 decompression inplace Gao Xiang
2019-08-02 12:53 ` [PATCH v6 22/24] erofs: introduce the decompression frontend Gao Xiang
2019-08-02 12:53 ` [PATCH v6 23/24] erofs: introduce cached decompression Gao Xiang
2019-08-02 12:53 ` [PATCH v6 24/24] erofs: add document Gao Xiang
2019-09-01  5:51 ` [PATCH 00/21] erofs: patchset addressing Christoph's comments Gao Xiang
2019-09-01  5:51   ` [PATCH 01/21] erofs: remove all the byte offset comments Gao Xiang
2019-09-02 12:05     ` Christoph Hellwig
2019-09-01  5:51   ` [PATCH 02/21] erofs: on-disk format should have explicitly assigned numbers Gao Xiang
2019-09-02 12:05     ` Christoph Hellwig
2019-09-01  5:51   ` [PATCH 03/21] erofs: some macros are much more readable as a function Gao Xiang
2019-09-02 12:06     ` Christoph Hellwig
2019-09-01  5:51   ` [PATCH 04/21] erofs: kill __packed for on-disk structures Gao Xiang
2019-09-02 12:06     ` Christoph Hellwig
2019-09-01  5:51   ` [PATCH 05/21] erofs: update erofs_inode_is_data_compressed helper Gao Xiang
2019-09-02 12:07     ` Christoph Hellwig
2019-09-01  5:51   ` [PATCH 06/21] erofs: kill erofs_{init,exit}_inode_cache Gao Xiang
2019-09-02 12:09     ` Christoph Hellwig
2019-09-01  5:51   ` [PATCH 07/21] erofs: use erofs_inode naming Gao Xiang
2019-09-02 12:10     ` Christoph Hellwig
2019-09-02 12:13       ` Gao Xiang
2019-09-02 12:47         ` Christoph Hellwig
2019-09-02 13:33           ` Gao Xiang
2019-09-01  5:51   ` [PATCH 08/21] erofs: update comments in inode.c Gao Xiang
2019-09-01  5:51   ` [PATCH 09/21] erofs: update erofs symlink stuffs Gao Xiang
2019-09-02 12:11     ` Christoph Hellwig
2019-09-01  5:51   ` [PATCH 10/21] erofs: kill is_inode_layout_compression() Gao Xiang
2019-09-02 12:11     ` Christoph Hellwig
2019-09-01  5:51   ` [PATCH 11/21] erofs: use dsb instead of layout for ondisk super_block Gao Xiang
2019-09-02 12:12     ` Christoph Hellwig
2019-09-02 12:15       ` Gao Xiang
2019-09-01  5:51   ` [PATCH 12/21] erofs: kill verbose debug info in erofs_fill_super Gao Xiang
2019-09-02 12:14     ` Christoph Hellwig
2019-09-02 12:18       ` Gao Xiang
2019-09-01  5:51   ` [PATCH 13/21] erofs: simplify erofs_grab_bio() since bio_alloc() never fail Gao Xiang
2019-09-02 12:20     ` Christoph Hellwig
2019-09-01  5:51   ` [PATCH 14/21] erofs: kill prio and nofail of erofs_get_meta_page() Gao Xiang
2019-09-02 12:21     ` Christoph Hellwig
2019-09-01  5:51   ` [PATCH 15/21] erofs: kill __submit_bio() Gao Xiang
2019-09-01  5:51   ` [PATCH 16/21] erofs: kill magic underscores Gao Xiang
2019-09-02 12:26     ` Christoph Hellwig
2019-09-02 12:39       ` Gao Xiang
2019-09-02 12:54         ` Christoph Hellwig
2019-09-02 13:38           ` Gao Xiang
2019-09-01  5:51   ` [PATCH 17/21] erofs: use a switch statement when dealing with the file modes Gao Xiang
2019-09-02 12:27     ` Christoph Hellwig
2019-09-01  5:51   ` [PATCH 18/21] erofs: add "erofs_" prefix for common and short functions Gao Xiang
2019-09-02 12:28     ` Christoph Hellwig
2019-09-01  5:51   ` [PATCH 19/21] erofs: kill all erofs specific fault injection Gao Xiang
2019-09-02 12:28     ` Christoph Hellwig
2019-09-01  5:51   ` [PATCH 20/21] erofs: kill use_vmap module parameter Gao Xiang
2019-09-02 12:31     ` Christoph Hellwig
2019-09-02 12:43       ` Gao Xiang
2019-09-01  5:51   ` [PATCH 21/21] erofs: save one level of indentation Gao Xiang
2019-09-02 12:31     ` Christoph Hellwig
2019-09-02 12:46   ` [PATCH 00/21] erofs: patchset addressing Christoph's comments Christoph Hellwig
2019-09-02 14:24     ` Gao Xiang
2019-09-02 15:23       ` Christoph Hellwig
2019-09-02 15:50         ` Gao Xiang
2019-09-03  6:58           ` Christoph Hellwig
2019-09-03  8:17             ` Gao Xiang
2019-09-03 15:37               ` Christoph Hellwig
2019-09-03 15:43                 ` Gao Xiang
2019-09-04  2:08   ` [PATCH v2 00/25] " Gao Xiang
2019-09-04  2:08     ` [PATCH v2 01/25] erofs: remove all the byte offset comments Gao Xiang
2019-09-04  2:08     ` [PATCH v2 02/25] erofs: on-disk format should have explicitly assigned numbers Gao Xiang
2019-09-04  2:08     ` [PATCH v2 03/25] erofs: some macros are much more readable as a function Gao Xiang
2019-09-04  2:08     ` [PATCH v2 04/25] erofs: kill __packed for on-disk structures Gao Xiang
2019-09-04  2:08     ` [PATCH v2 05/25] erofs: update erofs_inode_is_data_compressed helper Gao Xiang
2019-09-04  2:08     ` [PATCH v2 06/25] erofs: use feature_incompat rather than requirements Gao Xiang
2019-09-04  2:08     ` [PATCH v2 07/25] erofs: better naming for erofs inode related stuffs Gao Xiang
2019-09-04  2:08     ` [PATCH v2 08/25] erofs: kill erofs_{init,exit}_inode_cache Gao Xiang
2019-09-04  2:08     ` [PATCH v2 09/25] erofs: use erofs_inode naming Gao Xiang
2019-09-04  2:08     ` [PATCH v2 10/25] erofs: update erofs_fs.h comments Gao Xiang
2019-09-04  2:08     ` [PATCH v2 11/25] erofs: update comments in inode.c Gao Xiang
2019-09-04  2:08     ` [PATCH v2 12/25] erofs: better erofs symlink stuffs Gao Xiang
2019-09-04  2:09     ` [PATCH v2 13/25] erofs: use dsb instead of layout for ondisk super_block Gao Xiang
2019-09-04  2:09     ` [PATCH v2 14/25] erofs: kill verbose debug info in erofs_fill_super Gao Xiang
2019-09-04  2:09     ` [PATCH v2 15/25] erofs: localize erofs_grab_bio() Gao Xiang
2019-09-04  2:09     ` [PATCH v2 16/25] erofs: kill prio and nofail of erofs_get_meta_page() Gao Xiang
2019-09-04  2:09     ` [PATCH v2 17/25] erofs: kill __submit_bio() Gao Xiang
2019-09-04  2:09     ` [PATCH v2 18/25] erofs: add "erofs_" prefix for common and short functions Gao Xiang
2019-09-04  2:09     ` [PATCH v2 19/25] erofs: kill all erofs specific fault injection Gao Xiang
2019-09-04  2:09     ` [PATCH v2 20/25] erofs: kill use_vmap module parameter Gao Xiang
2019-09-04  2:09     ` [PATCH v2 21/25] erofs: save one level of indentation Gao Xiang
2019-09-04  2:09     ` [PATCH v2 22/25] erofs: rename errln/infoln/debugln to erofs_{err, info, dbg} Gao Xiang
2019-09-04  2:09     ` [PATCH v2 23/25] erofs: use read_mapping_page instead of sb_bread Gao Xiang
2019-09-04  2:09     ` [PATCH v2 24/25] erofs: always use iget5_locked Gao Xiang
2019-09-04  2:09     ` [PATCH v2 25/25] erofs: use read_cache_page_gfp for erofs_get_meta_page Gao Xiang
2019-09-04  3:27     ` [PATCH v2 00/25] erofs: patchset addressing Christoph's comments Chao Yu
2019-09-05  1:03       ` Gao Xiang
2019-09-05 11:30         ` Christoph Hellwig
2019-09-04  5:16     ` Christoph Hellwig
2019-09-04  6:08       ` Gao Xiang

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