Re: [PATCH 3/5] ext4: Implement ci comparison using fscrypt_name

[Eric Biggers <ebiggers@kernel.org>]

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@collabora.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?

- Eric