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Subject: Re: [f2fs-dev] [RFC PATCH 10/10] f2fs: fs-verity support
To:     Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <chao@kernel.org>
CC:     Eric Biggers <ebiggers@kernel.org>,
        Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
        Michael Halcrow <mhalcrow@google.com>,
        <linux-kernel@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>,
        <linux-fscrypt@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>,
        <linux-integrity@vger.kernel.org>, <linux-ext4@vger.kernel.org>,
        Mimi Zohar <zohar@linux.vnet.ibm.com>,
        Victor Hsieh <victorhsieh@google.com>
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 <dbc20be8-975d-7bd2-002d-a8f30896da4a@kernel.org>
 <20180828072756.GC29049@jaegeuk-macbookpro.roam.corp.google.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <63a19512-e938-d239-9e3c-f6ecc479478c@huawei.com>
Date:   Tue, 28 Aug 2018 17:20:01 +0800
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On 2018/8/28 15:27, Jaegeuk Kim wrote:
> On 08/27, Chao Yu wrote:
>> Hi Eric,
>>
>> On 2018/8/27 1:35, Eric Biggers wrote:
>>> Hi Chao,
>>>
>>> On Sat, Aug 25, 2018 at 01:54:08PM +0800, Chao Yu wrote:
>>>> On 2018/8/25 0:16, Eric Biggers wrote:
>>>>> From: Eric Biggers <ebiggers@google.com>
>>>>>  #ifdef CONFIG_F2FS_CHECK_FS
>>>>>  #define f2fs_bug_on(sbi, condition)	BUG_ON(condition)
>>>>>  #else
>>>>> @@ -146,7 +149,7 @@ struct f2fs_mount_info {
>>>>>  #define F2FS_FEATURE_QUOTA_INO		0x0080
>>>>>  #define F2FS_FEATURE_INODE_CRTIME	0x0100
>>>>>  #define F2FS_FEATURE_LOST_FOUND		0x0200
>>>>> -#define F2FS_FEATURE_VERITY		0x0400	/* reserved */
>>>>> +#define F2FS_FEATURE_VERITY		0x0400
>>>>>  
>>>>>  #define F2FS_HAS_FEATURE(sb, mask)					\
>>>>>  	((F2FS_SB(sb)->raw_super->feature & cpu_to_le32(mask)) != 0)
>>>>> @@ -598,7 +601,7 @@ enum {
>>>>>  #define FADVISE_ENC_NAME_BIT	0x08
>>>>>  #define FADVISE_KEEP_SIZE_BIT	0x10
>>>>>  #define FADVISE_HOT_BIT		0x20
>>>>> -#define FADVISE_VERITY_BIT	0x40	/* reserved */
>>>>> +#define FADVISE_VERITY_BIT	0x40
>>>>
>>>> As I suggested before, how about moving f2fs' verity_bit from i_fadvise to more
>>>> generic i_flags field like ext4, so we can a) remaining more bits for those
>>>> demands which really need file advise fields. b) using i_flags bits keeping line
>>>> with ext4. Not sure, if user want to know whether the file is verity one, it
>>>> will be easy for f2fs to export the status through FS_IOC_SETFLAGS.
>>>>
>>>> #define EXT4_VERITY_FL			0x00100000 /* Verity protected inode */
>>>>
>>>> #define F2FS_VERITY_FL			0x00100000 /* Verity protected inode */
>>>>
>>>
>>> I don't like using i_advise much either, but I actually don't see either
>>> location being much better than the other at the moment.  The real problem is an
>>> artificial one: the i_flags in f2fs's on-disk format are being assumed to use
>>
>> Yeah, but since most copied flags from vfs/ext4 are not actually used in f2fs,
>> also 0x00100000 bit is not used now, so we can just define it now directly for
>> verity bit.
>>
>> Cleanup and remapping in ioctl interface for those unused flags, we can do it
>> latter?
> 
> No, it was reserved by f2fs-tools, 

That's not a problem, since we didn't use that reserved bit in any of images
now, there is no backward compatibility issue.

> and I think this should be aligned to the encryption bit. 

Alright, we could, but if so, i_advise will run out of space earlier, after that
we have to add real advice bit into i_inline or i_flags, that would be a little
weird.

For encryption bit, as a common vfs feature flag, in the beginning of encryption
development, it will be better to set it into i_flags, IMO, but now, we have to
keep it as it was.

> Moreover, we guarantee i_flags less strictly from power-cut than i_advise.

IMO, in power-cut scenario, it needs to keep both i_flags and i_advise being
recoverable strictly. Any condition that we can not recover i_flags?

Thanks,

> 
>>
>> Thanks,
>>
>>> the same numbering scheme as ext4's on-disk format, which makes it seem that
>>> they have to be in sync, and that all new ext4 flags (say, EA_INODE) also
>>> reserve bits in f2fs and vice versa, when they in fact do not.  Instead, f2fs
>>> should use its own numbering for its i_flags, and it should map them to/from
>>> whatever is needed for common APIs like FS_IOC_{GET,SET}FLAGS and
>>> FS_IOC_FS{GET,SET}XATTR.
>>>
>>> So putting the verity flag in *either* location (i_advise or i_flags) is just
>>> kicking the can down the road.  If I get around to it I will send a patch that
>>> cleans up the f2fs flags properly...>
>>> Thanks,
>>>
>>> - Eric
>>>
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>>>
> 
> .
>