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Date:   Thu, 31 Mar 2022 21:43:05 +0000
From:   Eric Biggers <ebiggers@kernel.org>
To:     Gabriel Krisman Bertazi <krisman@collabora.com>
Cc:     tytso@mit.edu, jaegeuk@kernel.org, linux-ext4@vger.kernel.org,
        kernel@collabora.com
Subject: Re: [PATCH 3/5] ext4: Implement ci comparison using fscrypt_name
Message-ID: <YkYgaUsxBy2gcZte@gmail.com>
References: <20220322030004.148560-1-krisman@collabora.com>
 <20220322030004.148560-4-krisman@collabora.com>
 <YkJ4J0XNSkSSf2Xo@sol.localdomain>
 <87k0ccrb6v.fsf@collabora.com>
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On Tue, Mar 29, 2022 at 12:11:04PM -0400, Gabriel Krisman Bertazi wrote:
> Eric Biggers <ebiggers@kernel.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@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?
> 
> 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.
> 

Which function, specifically, are you trying to share across filesystems?
Do you have patches that show what your end goal is?

- Eric