Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v2 2/2] f2fs: Advertise encrypted casefolding in sysfs
To:     Jaegeuk Kim <jaegeuk@kernel.org>,
        Eric Biggers <ebiggers@kernel.org>
Cc:     Daniel Rosenberg <drosen@google.com>,
        linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Gabriel Krisman Bertazi <krisman@collabora.com>,
        kernel-team@android.com, stable@vger.kernel.org
References: <20210603095038.314949-1-drosen@google.com>
 <20210603095038.314949-3-drosen@google.com>
 <YLlj+h4RiT6FvyK6@sol.localdomain> <YLmv5Ykb3QUzDOlL@google.com>
 <YLmzkzPZwBVYf5LO@sol.localdomain> <YLm8aOs6Sc/CLaAv@google.com>
From:   Chao Yu <chao@kernel.org>
Message-ID: <452273b4-b386-3180-9b6e-f060bdbe3802@kernel.org>
Date:   Sat, 5 Jun 2021 08:11:32 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.10.2
MIME-Version: 1.0
In-Reply-To: <YLm8aOs6Sc/CLaAv@google.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2021/6/4 13:38, Jaegeuk Kim wrote:
> On 06/03, Eric Biggers wrote:
>> On Thu, Jun 03, 2021 at 09:45:25PM -0700, Jaegeuk Kim wrote:
>>> On 06/03, Eric Biggers wrote:
>>>> On Thu, Jun 03, 2021 at 09:50:38AM +0000, Daniel Rosenberg wrote:
>>>>> Older kernels don't support encryption with casefolding. This adds
>>>>> the sysfs entry encrypted_casefold to show support for those combined
>>>>> features. Support for this feature was originally added by
>>>>> commit 7ad08a58bf67 ("f2fs: Handle casefolding with Encryption")
>>>>>
>>>>> Fixes: 7ad08a58bf67 ("f2fs: Handle casefolding with Encryption")
>>>>> Cc: stable@vger.kernel.org # v5.11+
>>>>> Signed-off-by: Daniel Rosenberg <drosen@google.com>
>>>>> ---
>>>>>   fs/f2fs/sysfs.c | 15 +++++++++++++--
>>>>>   1 file changed, 13 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
>>>>> index 09e3f258eb52..6604291a3cdf 100644
>>>>> --- a/fs/f2fs/sysfs.c
>>>>> +++ b/fs/f2fs/sysfs.c
>>>>> @@ -161,6 +161,9 @@ static ssize_t features_show(struct f2fs_attr *a,
>>>>>   	if (f2fs_sb_has_compression(sbi))
>>>>>   		len += scnprintf(buf + len, PAGE_SIZE - len, "%s%s",
>>>>>   				len ? ", " : "", "compression");
>>>>> +	if (f2fs_sb_has_casefold(sbi) && f2fs_sb_has_encrypt(sbi))
>>>>> +		len += scnprintf(buf + len, PAGE_SIZE - len, "%s%s",
>>>>> +				len ? ", " : "", "encrypted_casefold");
>>>>>   	len += scnprintf(buf + len, PAGE_SIZE - len, "%s%s",
>>>>>   				len ? ", " : "", "pin_file");
>>>>>   	len += scnprintf(buf + len, PAGE_SIZE - len, "\n");
>>>>> @@ -579,6 +582,7 @@ enum feat_id {
>>>>>   	FEAT_CASEFOLD,
>>>>>   	FEAT_COMPRESSION,
>>>>>   	FEAT_TEST_DUMMY_ENCRYPTION_V2,
>>>>> +	FEAT_ENCRYPTED_CASEFOLD,
>>>>>   };
>>>>
>>>> Actually looking at it more closely, this patch is wrong.
>>>>
>>>> It only makes sense to declare "encrypted_casefold" as a feature of the
>>>> filesystem implementation, i.e. /sys/fs/f2fs/features/encrypted_casefold.
>>>>
>>>> It does *not* make sense to declare it as a feature of a particular filesystem
>>>> instance, i.e. /sys/fs/f2fs/$disk/features, as it is already implied by the
>>>> filesystem instance having both the encryption and casefold features enabled.
>>>>
>>>> Can we add /sys/fs/f2fs/features/encrypted_casefold only?
>>>
>>> wait.. /sys/fs/f2fs/features/encrypted_casefold is on by
>>> CONFIG_FS_ENCRYPTION && CONFIG_UNICODE.
>>> OTOH, /sys/fs/f2fs/$dis/feature_list/encrypted_casefold is on by
>>> on-disk features: F2FS_FEATURE_ENCRYPT and F2FS_FEATURE_CASEFOLD.
>>>
>>
>> Yes, but in the on-disk case, encrypted_casefold is redundant because it simply
>> means encrypt && casefold.  There is no encrypted_casefold flag on-disk.
> 
> I prefer to keep encrypted_casefold likewise kernel feature, which is more
> intuitive to users.

encrypted_casefold is a kernel feature support flag, not a disk one, IMO, it's
not needed to add it in to per-disk feature list, it may mislead user that
compatible encrypted casefold needs a extra disk layout support while disk has
already encrypted and casefold feature enabled.

Thanks,

> 
>>
>> - Eric