linux-ext4 - Re: [PATCH v2 4/7] libfs: Support revalidation of encrypted case-insensitive dentries

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Date:   Tue, 18 Jul 2023 15:34:13 -0400
From:   Gabriel Krisman Bertazi <krisman@...e.de>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     viro@...iv.linux.org.uk, brauner@...nel.org, tytso@....edu,
        jaegeuk@...nel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH v2 4/7] libfs: Support revalidation of encrypted
 case-insensitive dentries

Eric Biggers <ebiggers@...nel.org> writes:

> On Fri, Apr 21, 2023 at 08:03:07PM -0400, Gabriel Krisman Bertazi wrote:
>> From: Gabriel Krisman Bertazi <krisman@...labora.com>
>> 
>> Preserve the existing behavior for encrypted directories, by rejecting
>> negative dentries of encrypted+casefolded directories.  This allows
>> generic_ci_d_revalidate to be used by filesystems with both features
>> enabled, as long as the directory is either casefolded or encrypted, but
>> not both at the same time.
>> 
>> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
>> ---
>>  fs/libfs.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>> 
>> diff --git a/fs/libfs.c b/fs/libfs.c
>> index f8881e29c5d5..0886044db593 100644
>> --- a/fs/libfs.c
>> +++ b/fs/libfs.c
>> @@ -1478,6 +1478,9 @@ static inline int generic_ci_d_revalidate(struct dentry *dentry,
>>  		const struct inode *dir = READ_ONCE(parent->d_inode);
>>  
>>  		if (dir && needs_casefold(dir)) {
>> +			if (IS_ENCRYPTED(dir))
>> +				return 0;
>> +
>
> Why not allow negative dentries in case-insensitive encrypted directories?
> I can't think any reason why it wouldn't just work.

TBH, I'm not familiar with the details of combined encrypted+casefold
support to be confident it works.  This patch preserves the current
behavior of disabling them for encrypted+casefold directories.

I suspect it might require extra work that I'm not focusing on this
patchset.  For instance, what should be the order of
fscrypt_d_revalidate and the checks I'm adding here? Note we will start
creating negative dentries in casefold directories after patch 6/7, so
unless we disable it here, we will start calling fscrypt_d_revalidate
for negative+casefold.

Should I just drop this hunk?  Unless you are confident it works as is, I
prefer to add this support in stages and keep negative dentries of
encrypted+casefold directories disabled for now.

-- 
Gabriel Krisman Bertazi