Re: [PATCH v3 04/10] fscrypt: Drop d_revalidate once the key is added

[Gabriel Krisman Bertazi <krisman@suse.de>]

Eric Biggers <ebiggers@kernel.org> writes:

> On Fri, Jan 19, 2024 at 03:47:36PM -0300, Gabriel Krisman Bertazi wrote:
>> /*
>>  * When d_splice_alias() moves a directory's no-key alias to its plaintext alias
>>  * as a result of the encryption key being added, DCACHE_NOKEY_NAME must be
>>  * cleared.  Note that we don't have to support arbitrary moves of this flag
>>  * because fscrypt doesn't allow no-key names to be the source or target of a
>>  * rename().
>>  */
>>  static inline void fscrypt_handle_d_move(struct dentry *dentry)
>>  {
>>  	dentry->d_flags &= ~DCACHE_NOKEY_NAME;
>> +
>> +	/*
>> +	 * Save the d_revalidate call cost during VFS operations.  We
>> +	 * can do it because, when the key is available, the dentry
>> +	 * can't go stale and the key won't go away without eviction.
>> +	 */
>> +	if (dentry->d_op && dentry->d_op->d_revalidate == fscrypt_d_revalidate)
>> +		dentry->d_flags &= ~DCACHE_OP_REVALIDATE;
>>  }
>
> Is there any way to optimize this further for the case where fscrypt is not
> being used?  This is called unconditionally from d_move().  I've generally been
> trying to avoid things like this where the fscrypt support slows things down for
> everyone even when they're not using the feature.

The problem would be figuring out whether the filesystem has fscrypt
enabled.  I think we can rely on sb->s_cop always being set:

if (sb->s_cop)
   fscrypt_handle_d_move(dentry);

What do you think?

-- 
Gabriel Krisman Bertazi