Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [f2fs-dev] [RFC PATCH 10/10] f2fs: fs-verity support
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     Chao Yu <chao@kernel.org>, 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>
References: <20180824161642.1144-1-ebiggers@kernel.org>
 <20180824161642.1144-11-ebiggers@kernel.org>
 <b2b6a810-9605-15c8-b905-a4591c0cf3a5@huawei.com>
 <20180826173507.GC728@sol.localdomain>
 <dbc20be8-975d-7bd2-002d-a8f30896da4a@kernel.org>
 <20180828072756.GC29049@jaegeuk-macbookpro.roam.corp.google.com>
 <63a19512-e938-d239-9e3c-f6ecc479478c@huawei.com>
 <20180828170142.GB62482@jaegeuk-macbookpro.roam.corp.google.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <8b7f83db-810a-bdd6-85b0-1248dc14f8d7@huawei.com>
Date:   Wed, 29 Aug 2018 09:22:42 +0800
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101
 Thunderbird/52.9.1
MIME-Version: 1.0
In-Reply-To: <20180828170142.GB62482@jaegeuk-macbookpro.roam.corp.google.com>
Content-Type: text/plain; charset="windows-1252"
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 2018/8/29 1:01, Jaegeuk Kim wrote:
> On 08/28, Chao Yu wrote:
>> 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.
> 
> We're using that.

Oops, if it was in production, I agree to keep it in i_advice, otherwise, we
still can discuss its location.

> 
>>
>>> 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?
> 
> In __f2fs_ioc_setflags, f2fs_mark_inode_dirty_sync(inode, false);

Ah, that's right, do you remember why we treat them with different recoverable
level?

Thanks,

> 
>>
>> 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
>>>>>
>>>>> ------------------------------------------------------------------------------
>>>>> Check out the vibrant tech community on one of the world's most
>>>>> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
>>>>> _______________________________________________
>>>>> Linux-f2fs-devel mailing list
>>>>> Linux-f2fs-devel@lists.sourceforge.net
>>>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>>>>
>>>
>>> .
>>>
> 
> .
>