linux-kernel - Re: [PATCH v2 2/2] f2fs: Advertise encrypted casefolding in sysfs

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Date:   Sat, 5 Jun 2021 08:11:32 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>,
        Eric Biggers <ebiggers@...nel.org>
Cc:     Daniel Rosenberg <drosen@...gle.com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        kernel-team@...roid.com, stable@...r.kernel.org
Subject: Re: [PATCH v2 2/2] f2fs: Advertise encrypted casefolding in sysfs

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@...r.kernel.org # v5.11+
>>>>> Signed-off-by: Daniel Rosenberg <drosen@...gle.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