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Date:   Tue, 03 Dec 2019 14:31:16 -0500
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     Daniel Rosenberg <drosen@...gle.com>
Cc:     "Theodore Ts'o" <tytso@....edu>, linux-ext4@...r.kernel.org,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        linux-f2fs-devel@...ts.sourceforge.net,
        Eric Biggers <ebiggers@...nel.org>,
        linux-fscrypt@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH 4/8] vfs: Fold casefolding into vfs

Daniel Rosenberg <drosen@...gle.com> writes:

> Ext4 and F2fs are both using casefolding, and they, along with any other
> filesystem that adds the feature, will be using identical dentry_ops.
> Additionally, those dentry ops interfere with the dentry_ops required
> for fscrypt once we add support for casefolding and encryption.
> Moving this into the vfs removes code duplication as well as the
> complication with encryption.
>
> Currently this is pretty close to just moving the existing f2fs/ext4
> code up a level into the vfs, although there is a lot of room for
> improvement now.
>
> Signed-off-by: Daniel Rosenberg <drosen@...gle.com>
> ---
>  fs/dcache.c        | 35 +++++++++++++++++++++++++++++++++++
>  fs/namei.c         | 43 ++++++++++++++++++++++++++++++++++++++++---
>  include/linux/fs.h | 12 ++++++++++++
>  3 files changed, 87 insertions(+), 3 deletions(-)
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index f7931b682a0d..575f3c2c3f77 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -32,6 +32,7 @@
>  #include <linux/bit_spinlock.h>
>  #include <linux/rculist_bl.h>
>  #include <linux/list_lru.h>
> +#include <linux/unicode.h>
>  #include "internal.h"
>  #include "mount.h"
>  
> @@ -228,6 +229,13 @@ static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char
>  
>  #endif
>  
> +bool needs_casefold(const struct inode *dir)
> +{
> +	return IS_CASEFOLDED(dir) &&
> +			(!IS_ENCRYPTED(dir) || fscrypt_has_encryption_key(dir));
> +}
> +EXPORT_SYMBOL(needs_casefold);
> +
>  static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
>  {
>  	/*
> @@ -247,7 +255,19 @@ static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *c
>  	 * be no NUL in the ct/tcount data)
>  	 */
>  	const unsigned char *cs = READ_ONCE(dentry->d_name.name);
> +#ifdef CONFIG_UNICODE
> +	struct inode *parent = dentry->d_parent->d_inode;
>  
> +	if (unlikely(needs_casefold(parent))) {
> +		const struct qstr n1 = QSTR_INIT(cs, tcount);
> +		const struct qstr n2 = QSTR_INIT(ct, tcount);
> +		int result = utf8_strncasecmp(dentry->d_sb->s_encoding,
> +						&n1, &n2);
> +
> +		if (result >= 0 || sb_has_enc_strict_mode(dentry->d_sb))
> +			return result;
> +	}
> +#endif
>  	return dentry_string_cmp(cs, ct, tcount);
>  }
>  
> @@ -2404,7 +2424,22 @@ struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
>  	 * calculate the standard hash first, as the d_op->d_hash()
>  	 * routine may choose to leave the hash value unchanged.
>  	 */
> +#ifdef CONFIG_UNICODE
> +	unsigned char *hname = NULL;
> +	int hlen = name->len;
> +
> +	if (IS_CASEFOLDED(dir->d_inode)) {
> +		hname = kmalloc(PATH_MAX, GFP_ATOMIC);
> +		if (!hname)
> +			return ERR_PTR(-ENOMEM);
> +		hlen = utf8_casefold(dir->d_sb->s_encoding,
> +					name, hname, PATH_MAX);
> +	}
> +	name->hash = full_name_hash(dir, hname ?: name->name, hlen);
> +	kfree(hname);
> +#else
>  	name->hash = full_name_hash(dir, name->name, name->len);
> +#endif
>  	if (dir->d_flags & DCACHE_OP_HASH) {
>  		int err = dir->d_op->d_hash(dir, name);
>  		if (unlikely(err < 0))
> diff --git a/fs/namei.c b/fs/namei.c
> index 2dda552bcf7a..b8d5cb0994ec 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -39,6 +39,7 @@
>  #include <linux/bitops.h>
>  #include <linux/init_task.h>
>  #include <linux/uaccess.h>
> +#include <linux/unicode.h>
>  
>  #include "internal.h"
>  #include "mount.h"
> @@ -2062,6 +2063,10 @@ static inline u64 hash_name(const void *salt, const char *name)
>  static int link_path_walk(const char *name, struct nameidata *nd)
>  {
>  	int err;
> +#ifdef CONFIG_UNICODE
> +	char *hname = NULL;
> +	int hlen = 0;
> +#endif
>  
>  	if (IS_ERR(name))
>  		return PTR_ERR(name);
> @@ -2078,9 +2083,21 @@ static int link_path_walk(const char *name, struct nameidata *nd)
>  		err = may_lookup(nd);
>  		if (err)
>  			return err;
> -
> +#ifdef CONFIG_UNICODE
> +		if (needs_casefold(nd->path.dentry->d_inode)) {
> +			struct qstr str = QSTR_INIT(name, PATH_MAX);
> +
> +			hname = kmalloc(PATH_MAX, GFP_ATOMIC);
> +			if (!hname)
> +				return -ENOMEM;
> +			hlen = utf8_casefold(nd->path.dentry->d_sb->s_encoding,
> +						&str, hname, PATH_MAX);
> +		}
> +		hash_len = hash_name(nd->path.dentry, hname ?: name);
> +		kfree(hname);

It would be nice to reuse the memory allocation for the entire path walk
instead of allocating and freeing several times in a row.  Still not
ideal, but I don't see how we could not have at least one allocation here.

> +#else
>  		hash_len = hash_name(nd->path.dentry, name);
> -
> +#endif
>  		type = LAST_NORM;
>  		if (name[0] == '.') switch (hashlen_len(hash_len)) {
>  			case 2:
> @@ -2452,9 +2469,29 @@ EXPORT_SYMBOL(vfs_path_lookup);
>  static int lookup_one_len_common(const char *name, struct dentry *base,
>  				 int len, struct qstr *this)
>  {
> +#ifdef CONFIG_UNICODE
> +	char *hname = NULL;
> +	int hlen = len;
> +
> +	if (needs_casefold(base->d_inode)) {
> +		struct qstr str = QSTR_INIT(name, len);
> +
> +		hname = kmalloc(PATH_MAX, GFP_ATOMIC);
> +		if (!hname)
> +			return -ENOMEM;
> +		hlen = utf8_casefold(base->d_sb->s_encoding,
> +					&str, hname, PATH_MAX);
> +	}
> +	this->hash = full_name_hash(base, hname ?: name, hlen);
> +	kvfree(hname);
> +#else
> +	this->hash = full_name_hash(base, name, len);
> +#endif
>  	this->name = name;
>  	this->len = len;
> -	this->hash = full_name_hash(base, name, len);
> +#ifdef CONFIG_UNICODE
> +	kfree(hname);
> +#endif
>  	if (!len)
>  		return -EACCES;
>  
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index c159a8bdee8b..38d1c20f3e6f 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1382,6 +1382,12 @@ extern int send_sigurg(struct fown_struct *fown);
>  #define SB_ACTIVE	(1<<30)
>  #define SB_NOUSER	(1<<31)
>  
> +/* These flags relate to encoding and casefolding */
> +#define SB_ENC_STRICT_MODE_FL	(1 << 0)
> +
> +#define sb_has_enc_strict_mode(sb) \
> +	(sb->s_encoding_flags & SB_ENC_STRICT_MODE_FL)
> +
>  /*
>   *	Umount options
>   */
> @@ -1449,6 +1455,10 @@ struct super_block {
>  #endif
>  #ifdef CONFIG_FS_VERITY
>  	const struct fsverity_operations *s_vop;
> +#endif
> +#ifdef CONFIG_UNICODE
> +	struct unicode_map *s_encoding;
> +	__u16 s_encoding_flags;
>  #endif
>  	struct hlist_bl_head	s_roots;	/* alternate root dentries for NFS */
>  	struct list_head	s_mounts;	/* list of mounts; _not_ for fs use */
> @@ -2044,6 +2054,8 @@ static inline bool sb_rdonly(const struct super_block *sb) { return sb->s_flags
>  #define IS_WHITEOUT(inode)	(S_ISCHR(inode->i_mode) && \
>  				 (inode)->i_rdev == WHITEOUT_DEV)
>  
> +extern bool needs_casefold(const struct inode *dir);
> +
>  static inline bool HAS_UNMAPPED_ID(struct inode *inode)
>  {
>  	return !uid_valid(inode->i_uid) || !gid_valid(inode->i_gid);

-- 
Gabriel Krisman Bertazi

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