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Date: Thu, 31 Mar 2022 21:43:05 +0000
From: Eric Biggers <ebiggers@...nel.org>
To: Gabriel Krisman Bertazi <krisman@...labora.com>
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
On Tue, Mar 29, 2022 at 12:11:04PM -0400, Gabriel Krisman Bertazi wrote:
> 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.
>
Which function, specifically, are you trying to share across filesystems?
Do you have patches that show what your end goal is?
- Eric
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