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 <npiggin@kernel.dk>

2 files changed, 28 insertions, 19 deletions

diff --git a/fs/fat/namei_msdos.c b/fs/fat/namei_msdos.c
index 3345aabd1dd7..99d3c7ac973c 100644
--- a/fs/fat/namei_msdos.c
+++ b/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 @@ out:
 
 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;
 }
 
diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
index b936703b8924..95e00ab84c3f 100644
--- a/fs/fat/namei_vfat.c
+++ b/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;