fs: change d_compare for rcu-walk

Change d_compare so it may be called from lock-free RCU lookups. This
does put significant restrictions on what may be done from the callback,
however there don't seem to have been any problems with in-tree fses.
If some strange use case pops up that _really_ cannot cope with the
rcu-walk rules, we can just add new rcu-unaware callbacks, which would
cause name lookup to drop out of rcu-walk mode.

For in-tree filesystems, this is just a mechanical change.

Signed-off-by: Nick Piggin <[email protected]>

Documentation/filesystems/Locking

@@ -11,7 +11,9 @@ be able to use diff(1).
 prototypes:
 	int (*d_revalidate)(struct dentry *, int);
 	int (*d_hash) (struct dentry *, struct qstr *);
-	int (*d_compare) (struct dentry *, struct qstr *, struct qstr *);
+	int (*d_compare)(const struct dentry *, const struct inode *,
+			const struct dentry *, const struct inode *,
+			unsigned int, const char *, const struct qstr *);
 	int (*d_delete)(struct dentry *);
 	void (*d_release)(struct dentry *);
 	void (*d_iput)(struct dentry *, struct inode *);

Documentation/filesystems/porting

@@ -326,3 +326,10 @@ to it.
 unreferenced dentries, and is now only called when the dentry refcount goes to
 0. Even on 0 refcount transition, it must be able to tolerate being called 0,
 1, or more times (eg. constant, idempotent).
+
+---
+[mandatory]
+
+	.d_compare() calling convention and locking rules are significantly
+changed. Read updated documentation in Documentation/filesystems/vfs.txt (and
+look at examples of other filesystems) for guidance.

Documentation/filesystems/vfs.txt

@@ -848,7 +848,9 @@ defined:
 struct dentry_operations {
 	int (*d_revalidate)(struct dentry *, struct nameidata *);
 	int (*d_hash)(struct dentry *, struct qstr *);
-	int (*d_compare)(struct dentry *, struct qstr *, struct qstr *);
+	int (*d_compare)(const struct dentry *, const struct inode *,
+			const struct dentry *, const struct inode *,
+			unsigned int, const char *, const struct qstr *);
 	int (*d_delete)(const struct dentry *);
 	void (*d_release)(struct dentry *);
 	void (*d_iput)(struct dentry *, struct inode *);
@@ -860,9 +862,27 @@ struct dentry_operations {
 	dcache. Most filesystems leave this as NULL, because all their
 	dentries in the dcache are valid
 
-  d_hash: called when the VFS adds a dentry to the hash table
+  d_hash: called when the VFS adds a dentry to the hash table. The first
+	dentry passed to d_hash is the parent directory that the name is
+	to be hashed into.
 
-  d_compare: called when a dentry should be compared with another
+  d_compare: called to compare a dentry name with a given name. The first
+	dentry is the parent of the dentry to be compared, the second is
+	the parent's inode, then the dentry and inode (may be NULL) of the
+	child dentry. len and name string are properties of the dentry to be
+	compared. qstr is the name to compare it with.
+
+	Must be constant and idempotent, and should not take locks if
+	possible, and should not or store into the dentry or inodes.
+	Should not dereference pointers outside the dentry or inodes without
+	lots of care (eg.  d_parent, d_inode, d_name should not be used).
+
+	However, our vfsmount is pinned, and RCU held, so the dentries and
+	inodes won't disappear, neither will our sb or filesystem module.
+	->i_sb and ->d_sb may be used.
+
+	It is a tricky calling convention because it needs to be called under
+	"rcu-walk", ie. without any locks or references on things.
 
   d_delete: called when the last reference to a dentry is dropped and the
 	dcache is deciding whether or not to cache it. Return 1 to delete

drivers/staging/smbfs/dir.c

@@ -275,7 +275,10 @@ smb_dir_open(struct inode *dir, struct file *file)
  */
 static int smb_lookup_validate(struct dentry *, struct nameidata *);
 static int smb_hash_dentry(struct dentry *, struct qstr *);
-static int smb_compare_dentry(struct dentry *, struct qstr *, struct qstr *);
+static int smb_compare_dentry(const struct dentry *,
+		const struct inode *,
+		const struct dentry *, const struct inode *,
+		unsigned int, const char *, const struct qstr *);
 static int smb_delete_dentry(const struct dentry *);
 
 static const struct dentry_operations smbfs_dentry_operations =
@@ -347,14 +350,17 @@ smb_hash_dentry(struct dentry *dir, struct qstr *this)
 }
 
 static int
-smb_compare_dentry(struct dentry *dir, struct qstr *a, struct qstr *b)
+smb_compare_dentry(const struct dentry *parent,
+		const struct inode *pinode,
+		const struct dentry *dentry, const struct inode *inode,
+		unsigned int len, const char *str, const struct qstr *name)
 {
 	int i, result = 1;
 
-	if (a->len != b->len)
+	if (len != name->len)
 		goto out;
-	for (i=0; i < a->len; i++) {
-		if (tolower(a->name[i]) != tolower(b->name[i]))
+	for (i=0; i < len; i++) {
+		if (tolower(str[i]) != tolower(name->name[i]))
 			goto out;
 	}
 	result = 0;

fs/adfs/dir.c

@@ -237,17 +237,19 @@ adfs_hash(struct dentry *parent, struct qstr *qstr)
  * requirements of the underlying filesystem.
  */
 static int
-adfs_compare(struct dentry *parent, struct qstr *entry, struct qstr *name)
+adfs_compare(const struct dentry *parent, const struct inode *pinode,
+		const struct dentry *dentry, const struct inode *inode,
+		unsigned int len, const char *str, const struct qstr *name)
 {
 	int i;
 
-	if (entry->len != name->len)
+	if (len != name->len)
 		return 1;
 
 	for (i = 0; i < name->len; i++) {
 		char a, b;
 
-		a = entry->name[i];
+		a = str[i];
 		b = name->name[i];
 
 		if (a >= 'A' && a <= 'Z')

fs/affs/namei.c

@@ -14,10 +14,16 @@ typedef int (*toupper_t)(int);
 
 static int	 affs_toupper(int ch);
 static int	 affs_hash_dentry(struct dentry *, struct qstr *);
-static int       affs_compare_dentry(struct dentry *, struct qstr *, struct qstr *);
+static int       affs_compare_dentry(const struct dentry *parent,
+		const struct inode *pinode,
+		const struct dentry *dentry, const struct inode *inode,
+		unsigned int len, const char *str, const struct qstr *name);
 static int	 affs_intl_toupper(int ch);
 static int	 affs_intl_hash_dentry(struct dentry *, struct qstr *);
-static int       affs_intl_compare_dentry(struct dentry *, struct qstr *, struct qstr *);
+static int       affs_intl_compare_dentry(const struct dentry *parent,
+		const struct inode *pinode,
+		const struct dentry *dentry, const struct inode *inode,
+		unsigned int len, const char *str, const struct qstr *name);
 
 const struct dentry_operations affs_dentry_operations = {
 	.d_hash		= affs_hash_dentry,
@@ -88,29 +94,29 @@ affs_intl_hash_dentry(struct dentry *dentry, struct qstr *qstr)
 	return __affs_hash_dentry(dentry, qstr, affs_intl_toupper);
 }
 
-static inline int
-__affs_compare_dentry(struct dentry *dentry, struct qstr *a, struct qstr *b, toupper_t toupper)
+static inline int __affs_compare_dentry(unsigned int len,
+		const char *str, const struct qstr *name, toupper_t toupper)
 {
-	const u8 *aname = a->name;
-	const u8 *bname = b->name;
-	int len;
+	const u8 *aname = str;
+	const u8 *bname = name->name;
 
-	/* 'a' is the qstr of an already existing dentry, so the name
-	 * must be valid. 'b' must be validated first.
+	/*
+	 * 'str' is the name of an already existing dentry, so the name
+	 * must be valid. 'name' must be validated first.
 	 */
 
-	if (affs_check_name(b->name,b->len))
+	if (affs_check_name(name->name, name->len))
 		return 1;
 
-	/* If the names are longer than the allowed 30 chars,
+	/*
+	 * If the names are longer than the allowed 30 chars,
 	 * the excess is ignored, so their length may differ.
 	 */
-	len = a->len;
 	if (len >= 30) {
-		if (b->len < 30)
+		if (name->len < 30)
 			return 1;
 		len = 30;
-	} else if (len != b->len)
+	} else if (len != name->len)
 		return 1;
 
 	for (; len > 0; len--)
@@ -121,14 +127,18 @@ __affs_compare_dentry(struct dentry *dentry, struct qstr *a, struct qstr *b, tou
 }
 
 static int
-affs_compare_dentry(struct dentry *dentry, struct qstr *a, struct qstr *b)
+affs_compare_dentry(const struct dentry *parent, const struct inode *pinode,
+		const struct dentry *dentry, const struct inode *inode,
+		unsigned int len, const char *str, const struct qstr *name)
 {
-	return __affs_compare_dentry(dentry, a, b, affs_toupper);
+	return __affs_compare_dentry(len, str, name, affs_toupper);
 }
 static int
-affs_intl_compare_dentry(struct dentry *dentry, struct qstr *a, struct qstr *b)
+affs_intl_compare_dentry(const struct dentry *parent,const struct inode *pinode,
+		const struct dentry *dentry, const struct inode *inode,
+		unsigned int len, const char *str, const struct qstr *name)
 {
-	return __affs_compare_dentry(dentry, a, b, affs_intl_toupper);
+	return __affs_compare_dentry(len, str, name, affs_intl_toupper);
 }
 
 /*

fs/cifs/dir.c

@@ -715,13 +715,15 @@ static int cifs_ci_hash(struct dentry *dentry, struct qstr *q)
 	return 0;
 }
 
-static int cifs_ci_compare(struct dentry *dentry, struct qstr *a,
-			   struct qstr *b)
+static int cifs_ci_compare(const struct dentry *parent,
+		const struct inode *pinode,
+		const struct dentry *dentry, const struct inode *inode,
+		unsigned int len, const char *str, const struct qstr *name)
 {
-	struct nls_table *codepage = CIFS_SB(dentry->d_inode->i_sb)->local_nls;
+	struct nls_table *codepage = CIFS_SB(pinode->i_sb)->local_nls;
 
-	if ((a->len == b->len) &&
-	    (nls_strnicmp(codepage, a->name, b->name, a->len) == 0))
+	if ((name->len == len) &&
+	    (nls_strnicmp(codepage, name->name, str, len) == 0))
 		return 0;
 	return 1;
 }

fs/dcache.c

@@ -1437,7 +1437,9 @@ struct dentry * __d_lookup(struct dentry * parent, struct qstr * name)
 		 */
 		qstr = &dentry->d_name;
 		if (parent->d_op && parent->d_op->d_compare) {
-			if (parent->d_op->d_compare(parent, qstr, name))
+			if (parent->d_op->d_compare(parent, parent->d_inode,
+						dentry, dentry->d_inode,
+						qstr->len, qstr->name, name))
 				goto next;
 		} else {
 			if (qstr->len != len)

fs/fat/namei_msdos.c

@@ -164,16 +164,18 @@ static int msdos_hash(struct dentry *dentry, struct qstr *qstr)
  * Compare two msdos names. If either of the names are invalid,
  * we fall back to doing the standard name comparison.
  */
-static int msdos_cmp(struct dentry *dentry, struct qstr *a, struct qstr *b)
+static int msdos_cmp(const struct dentry *parent, const struct inode *pinode,
+		const struct dentry *dentry, const struct inode *inode,
+		unsigned int len, const char *str, const struct qstr *name)
 {
-	struct fat_mount_options *options = &MSDOS_SB(dentry->d_sb)->options;
+	struct fat_mount_options *options = &MSDOS_SB(parent->d_sb)->options;
 	unsigned char a_msdos_name[MSDOS_NAME], b_msdos_name[MSDOS_NAME];
 	int error;
 
-	error = msdos_format_name(a->name, a->len, a_msdos_name, options);
+	error = msdos_format_name(name->name, name->len, a_msdos_name, options);
 	if (error)
 		goto old_compare;
-	error = msdos_format_name(b->name, b->len, b_msdos_name, options);
+	error = msdos_format_name(str, len, b_msdos_name, options);
 	if (error)
 		goto old_compare;
 	error = memcmp(a_msdos_name, b_msdos_name, MSDOS_NAME);
@@ -182,8 +184,8 @@ static int msdos_cmp(struct dentry *dentry, struct qstr *a, struct qstr *b)
 
 old_compare:
 	error = 1;
-	if (a->len == b->len)
-		error = memcmp(a->name, b->name, a->len);
+	if (name->len == len)
+		error = memcmp(name->name, str, len);
 	goto out;
 }
 

fs/fat/namei_vfat.c

@@ -85,15 +85,18 @@ static int vfat_revalidate_ci(struct dentry *dentry, struct nameidata *nd)
 }
 
 /* returns the length of a struct qstr, ignoring trailing dots */
-static unsigned int vfat_striptail_len(struct qstr *qstr)
+static unsigned int __vfat_striptail_len(unsigned int len, const char *name)
 {
-	unsigned int len = qstr->len;
-
-	while (len && qstr->name[len - 1] == '.')
+	while (len && name[len - 1] == '.')
 		len--;
 	return len;
 }
 
+static unsigned int vfat_striptail_len(const struct qstr *qstr)
+{
+	return __vfat_striptail_len(qstr->len, qstr->name);
+}
+
 /*
  * Compute the hash for the vfat name corresponding to the dentry.
  * Note: if the name is invalid, we leave the hash code unchanged so
@@ -133,16 +136,18 @@ static int vfat_hashi(struct dentry *dentry, struct qstr *qstr)
 /*
  * Case insensitive compare of two vfat names.
  */
-static int vfat_cmpi(struct dentry *dentry, struct qstr *a, struct qstr *b)
+static int vfat_cmpi(const struct dentry *parent, const struct inode *pinode,
+		const struct dentry *dentry, const struct inode *inode,
+		unsigned int len, const char *str, const struct qstr *name)
 {
-	struct nls_table *t = MSDOS_SB(dentry->d_inode->i_sb)->nls_io;
+	struct nls_table *t = MSDOS_SB(parent->d_sb)->nls_io;
 	unsigned int alen, blen;
 
 	/* A filename cannot end in '.' or we treat it like it has none */
-	alen = vfat_striptail_len(a);
-	blen = vfat_striptail_len(b);
+	alen = vfat_striptail_len(name);
+	blen = __vfat_striptail_len(len, str);
 	if (alen == blen) {
-		if (nls_strnicmp(t, a->name, b->name, alen) == 0)
+		if (nls_strnicmp(t, name->name, str, alen) == 0)
 			return 0;
 	}
 	return 1;
@@ -151,15 +156,17 @@ static int vfat_cmpi(struct dentry *dentry, struct qstr *a, struct qstr *b)
 /*
  * Case sensitive compare of two vfat names.
  */
-static int vfat_cmp(struct dentry *dentry, struct qstr *a, struct qstr *b)
+static int vfat_cmp(const struct dentry *parent, const struct inode *pinode,
+		const struct dentry *dentry, const struct inode *inode,
+		unsigned int len, const char *str, const struct qstr *name)
 {
 	unsigned int alen, blen;
 
 	/* A filename cannot end in '.' or we treat it like it has none */
-	alen = vfat_striptail_len(a);
-	blen = vfat_striptail_len(b);
+	alen = vfat_striptail_len(name);
+	blen = __vfat_striptail_len(len, str);
 	if (alen == blen) {
-		if (strncmp(a->name, b->name, alen) == 0)
+		if (strncmp(name->name, str, alen) == 0)
 			return 0;
 	}
 	return 1;

fs/hfs/hfs_fs.h

@@ -216,7 +216,10 @@ extern const struct dentry_operations hfs_dentry_operations;
 extern int hfs_hash_dentry(struct dentry *, struct qstr *);
 extern int hfs_strcmp(const unsigned char *, unsigned int,
 		      const unsigned char *, unsigned int);
-extern int hfs_compare_dentry(struct dentry *, struct qstr *, struct qstr *);
+extern int hfs_compare_dentry(const struct dentry *parent,
+		const struct inode *pinode,
+		const struct dentry *dentry, const struct inode *inode,
+		unsigned int len, const char *str, const struct qstr *name);
 
 /* trans.c */
 extern void hfs_asc2mac(struct super_block *, struct hfs_name *, struct qstr *);

fs/hfs/string.c

@@ -92,21 +92,21 @@ int hfs_strcmp(const unsigned char *s1, unsigned int len1,
  * Test for equality of two strings in the HFS filename character ordering.
  * return 1 on failure and 0 on success
  */
-int hfs_compare_dentry(struct dentry *dentry, struct qstr *s1, struct qstr *s2)
+int hfs_compare_dentry(const struct dentry *parent, const struct inode *pinode,
+		const struct dentry *dentry, const struct inode *inode,
+		unsigned int len, const char *str, const struct qstr *name)
 {
 	const unsigned char *n1, *n2;
-	int len;
 
-	len = s1->len;
 	if (len >= HFS_NAMELEN) {
-		if (s2->len < HFS_NAMELEN)
+		if (name->len < HFS_NAMELEN)
 			return 1;
 		len = HFS_NAMELEN;
-	} else if (len != s2->len)
+	} else if (len != name->len)
 		return 1;
 
-	n1 = s1->name;
-	n2 = s2->name;
+	n1 = str;
+	n2 = name->name;
 	while (len--) {
 		if (caseorder[*n1++] != caseorder[*n2++])
 			return 1;

fs/hfsplus/hfsplus_fs.h

@@ -380,7 +380,10 @@ int hfsplus_strcmp(const struct hfsplus_unistr *, const struct hfsplus_unistr *)
 int hfsplus_uni2asc(struct super_block *, const struct hfsplus_unistr *, char *, int *);
 int hfsplus_asc2uni(struct super_block *, struct hfsplus_unistr *, const char *, int);
 int hfsplus_hash_dentry(struct dentry *dentry, struct qstr *str);
-int hfsplus_compare_dentry(struct dentry *dentry, struct qstr *s1, struct qstr *s2);
+int hfsplus_compare_dentry(const struct dentry *parent,
+		const struct inode *pinode,
+		const struct dentry *dentry, const struct inode *inode,
+		unsigned int len, const char *str, const struct qstr *name);
 
 /* wrapper.c */
 int hfsplus_read_wrapper(struct super_block *);