linux-ext4 - Re: [PATCH 3/5] ext4: Implement ci comparison using fscrypt

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Date:   Tue, 29 Mar 2022 12:11:04 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     tytso@....edu, jaegeuk@...nel.org, linux-ext4@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCH 3/5] ext4: Implement ci comparison using fscrypt_name

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

> On Mon, Mar 21, 2022 at 11:00:02PM -0400, Gabriel Krisman Bertazi wrote:
>> By using fscrypt_name here, we can hide most of the caching casefold
>> logic from ext4.  The condition in ext4_match is now quite redundant,
>> but this is addressed in the next patch.
>> 
>> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
>> ---
>>  fs/ext4/namei.c         | 26 ++++++++++++--------------
>>  include/linux/fscrypt.h |  4 ++++
>>  2 files changed, 16 insertions(+), 14 deletions(-)
>> 
>> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
>> index 8976e5a28c73..71b4b05fae89 100644
>> --- a/fs/ext4/namei.c
>> +++ b/fs/ext4/namei.c
>> @@ -1321,10 +1321,9 @@ static void dx_insert_block(struct dx_frame *frame, u32 hash, ext4_lblk_t block)
>>  /**
>>   * ext4_ci_compare() - Match (case-insensitive) a name with a dirent.
>>   * @parent: Inode of the parent of the dentry.
>> - * @name: name under lookup.
>> + * @fname: name under lookup.
>>   * @de_name: Dirent name.
>>   * @de_name_len: dirent name length.
>> - * @quick: whether @name is already casefolded.
>>   *
>>   * Test whether a case-insensitive directory entry matches the filename
>>   * being searched.  If quick is set, the @name being looked up is
>> @@ -1333,8 +1332,9 @@ static void dx_insert_block(struct dx_frame *frame, u32 hash, ext4_lblk_t block)
>>   * Return: > 0 if the directory entry matches, 0 if it doesn't match, or
>>   * < 0 on error.
>>   */
>> -static int ext4_ci_compare(const struct inode *parent, const struct qstr *name,
>> -			   u8 *de_name, size_t de_name_len, bool quick)
>> +static int ext4_ci_compare(const struct inode *parent,
>> +			   const struct fscrypt_name *fname,
>> +			   u8 *de_name, size_t de_name_len)
>>  {
>>  	const struct super_block *sb = parent->i_sb;
>>  	const struct unicode_map *um = sb->s_encoding;
>> @@ -1357,10 +1357,10 @@ static int ext4_ci_compare(const struct inode *parent, const struct qstr *name,
>>  		entry.len = decrypted_name.len;
>>  	}
>>  
>> -	if (quick)
>> -		ret = utf8_strncasecmp_folded(um, name, &entry);
>> +	if (fname->cf_name.name)
>> +		ret = utf8_strncasecmp_folded(um, &fname->cf_name, &entry);
>>  	else
>> -		ret = utf8_strncasecmp(um, name, &entry);
>> +		ret = utf8_strncasecmp(um, fname->usr_fname, &entry);
>>  
>>  	if (!ret)
>>  		match = true;
>> @@ -1370,8 +1370,8 @@ static int ext4_ci_compare(const struct inode *parent, const struct qstr *name,
>>  		 * the names have invalid characters.
>>  		 */
>>  		ret = 0;
>> -		match = ((name->len == entry.len) &&
>> -			 !memcmp(name->name, entry.name, entry.len));
>> +		match = ((fname->usr_fname->len == entry.len) &&
>> +			 !memcmp(fname->usr_fname->name, entry.name, entry.len));
>>  	}
>>  
>>  out:
>> @@ -1440,6 +1440,8 @@ static bool ext4_match(struct inode *parent,
>>  #endif
>>  
>>  #if IS_ENABLED(CONFIG_UNICODE)
>> +	f.cf_name = fname->cf_name;
>> +
>>  	if (parent->i_sb->s_encoding && IS_CASEFOLDED(parent) &&
>>  	    (!IS_ENCRYPTED(parent) || fscrypt_has_encryption_key(parent))) {
>>  		if (fname->cf_name.name) {
>> @@ -1451,13 +1453,9 @@ static bool ext4_match(struct inode *parent,
>>  					return false;
>>  				}
>>  			}
>> -			ret = ext4_ci_compare(parent, &fname->cf_name, de->name,
>> -					      de->name_len, true);
>> -		} else {
>> -			ret = ext4_ci_compare(parent, fname->usr_fname,
>> -					      de->name, de->name_len, false);
>>  		}
>>  
>> +		ret = ext4_ci_compare(parent, &f, de->name, de->name_len);
>>  		if (ret < 0) {
>>  			/*
>>  			 * Treat comparison errors as not a match.  The
>> diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
>> index 91ea9477e9bd..5dc4b3c805e4 100644
>> --- a/include/linux/fscrypt.h
>> +++ b/include/linux/fscrypt.h
>> @@ -36,6 +36,10 @@ struct fscrypt_name {
>>  	u32 minor_hash;
>>  	struct fscrypt_str crypto_buf;
>>  	bool is_nokey_name;
>> +
>> +#ifdef CONFIG_UNICODE
>> +	struct qstr cf_name;
>> +#endif
>>  };
>>  
>
> This seems like the wrong approach.  struct fscrypt_name shouldn't have fields
> that aren't used by the fs/crypto/ layer.
>
> Did you check what f2fs does?  It has a struct f2fs_filename to represent
> everything f2fs needs to know about a filename, and it only uses
> struct fscrypt_name when communicating with the fs/crypto/ layer.
>
> struct ext4_filename already exists.  Couldn't you use that here?

Hi Eric,

The reason I'm not using struct ext4_filename here is because I'm trying
to make this generic, so this function can be shared across filesystems
implementing casefold.  Since the fscrypt_name abstraction is used for
case-sensitive comparison, I was trying to reuse that type for
case-insensitive as well.  It seemed unnecessary to define a generic
casefold_name type just for passing the cf_name and disk_name to this
function, considering that fscrypt_name is already initialized by
ext4_match.

-- 
Gabriel Krisman Bertazi