new helper: d_same_name()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 36 insertions, 91 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index dc37c0238b46..040c2586d483 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2066,42 +2066,19 @@ struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
 }
 EXPORT_SYMBOL(d_add_ci);
 
-/*
- * Do the slow-case of the dentry name compare.
- *
- * Unlike the dentry_cmp() function, we need to atomically
- * load the name and length information, so that the
- * filesystem can rely on them, and can use the 'name' and
- * 'len' information without worrying about walking off the
- * end of memory etc.
- *
- * Thus the read_seqcount_retry() and the "duplicate" info
- * in arguments (the low-level filesystem should not look
- * at the dentry inode or name contents directly, since
- * rename can change them while we're in RCU mode).
- */
-enum slow_d_compare {
-        D_COMP_OK,
-        D_COMP_NOMATCH,
-        D_COMP_SEQRETRY,
-};
 
-static noinline enum slow_d_compare slow_dentry_cmp(
-                const struct dentry *parent,
-                struct dentry *dentry,
-                unsigned int seq,
-                const struct qstr *name)
+static inline bool d_same_name(const struct dentry *dentry,
+                                const struct dentry *parent,
+                                const struct qstr *name)
 {
-        int tlen = dentry->d_name.len;
-        const char *tname = dentry->d_name.name;
-
-        if (read_seqcount_retry(&dentry->d_seq, seq)) {
-                cpu_relax();
-                return D_COMP_SEQRETRY;
+        if (likely(!(parent->d_flags & DCACHE_OP_COMPARE))) {
+                if (dentry->d_name.len != name->len)
+                        return false;
+                return dentry_cmp(dentry, name->name, name->len) == 0;
         }
-        if (parent->d_op->d_compare(parent, dentry, tlen, tname, name))
-                return D_COMP_NOMATCH;
-        return D_COMP_OK;
+        return parent->d_op->d_compare(parent, dentry,
+                                       dentry->d_name.len, dentry->d_name.name,
+                                       name) == 0;
 }
 
 /**
@@ -2180,6 +2157,9 @@ seqretry:
                  * dentry compare, we will do seqretries until it is stable,
                  * and if we end up with a successful lookup, we actually
                  * want to exit RCU lookup anyway.
+                 *
+                 * Note that raw_seqcount_begin still *does* smp_rmb(), so
+                 * we are still guaranteed NUL-termination of ->d_name.name.
                  */
                 seq = raw_seqcount_begin(&dentry->d_seq);
                 if (dentry->d_parent != parent)
@@ -2188,24 +2168,28 @@ seqretry:
                         continue;
 
                 if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
+                        int tlen;
+                        const char *tname;
                         if (dentry->d_name.hash != hashlen_hash(hashlen))
                                 continue;
-                        *seqp = seq;
-                        switch (slow_dentry_cmp(parent, dentry, seq, name)) {
-                        case D_COMP_OK:
-                                return dentry;
-                        case D_COMP_NOMATCH:
-                                continue;
-                        default:
+                        tlen = dentry->d_name.len;
+                        tname = dentry->d_name.name;
+                        /* we want a consistent (name,len) pair */
+                        if (read_seqcount_retry(&dentry->d_seq, seq)) {
+                                cpu_relax();
                                 goto seqretry;
                         }
+                        if (parent->d_op->d_compare(parent, dentry,
+                                                    tlen, tname, name) != 0)
+                                continue;
+                } else {
+                        if (dentry->d_name.hash_len != hashlen)
+                                continue;
+                        if (dentry_cmp(dentry, str, hashlen_len(hashlen)) != 0)
+                                continue;
                 }
-
-                if (dentry->d_name.hash_len != hashlen)
-                        continue;
                 *seqp = seq;
-                if (!dentry_cmp(dentry, str, hashlen_len(hashlen)))
-                        return dentry;
+                return dentry;
         }
         return NULL;
 }
@@ -2253,9 +2237,7 @@ EXPORT_SYMBOL(d_lookup);
  */
 struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
 {
-        unsigned int len = name->len;
         unsigned int hash = name->hash;
-        const unsigned char *str = name->name;
         struct hlist_bl_head *b = d_hash(parent, hash);
         struct hlist_bl_node *node;
         struct dentry *found = NULL;
@@ -2294,21 +2276,8 @@ struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
                 if (d_unhashed(dentry))
                         goto next;
 
-                /*
-                 * It is safe to compare names since d_move() cannot
-                 * change the qstr (protected by d_lock).
-                 */
-                if (parent->d_flags & DCACHE_OP_COMPARE) {
-                        int tlen = dentry->d_name.len;
-                        const char *tname = dentry->d_name.name;
-                        if (parent->d_op->d_compare(parent, dentry, tlen, tname, name))
-                                goto next;
-                } else {
-                        if (dentry->d_name.len != len)
-                                goto next;
-                        if (dentry_cmp(dentry, str, len))
-                                goto next;
-                }
+                if (!d_same_name(dentry, parent, name))
+                        goto next;
 
                 dentry->d_lockref.count++;
                 found = dentry;
@@ -2461,9 +2430,7 @@ struct dentry *d_alloc_parallel(struct dentry *parent,
                                 const struct qstr *name,
                                 wait_queue_head_t *wq)
 {
-        unsigned int len = name->len;
         unsigned int hash = name->hash;
-        const unsigned char *str = name->name;
         struct hlist_bl_head *b = in_lookup_hash(parent, hash);
         struct hlist_bl_node *node;
         struct dentry *new = d_alloc(parent, name);
@@ -2514,17 +2481,8 @@ retry:
                         continue;
                 if (dentry->d_parent != parent)
                         continue;
-                if (parent->d_flags & DCACHE_OP_COMPARE) {
-                        int tlen = dentry->d_name.len;
-                        const char *tname = dentry->d_name.name;
-                        if (parent->d_op->d_compare(parent, dentry, tlen, tname, name))
-                                continue;
-                } else {
-                        if (dentry->d_name.len != len)
-                                continue;
-                        if (dentry_cmp(dentry, str, len))
-                                continue;
-                }
+                if (!d_same_name(dentry, parent, name))
+                        continue;
                 hlist_bl_unlock(b);
                 /* now we can try to grab a reference */
                 if (!lockref_get_not_dead(&dentry->d_lockref)) {
@@ -2551,17 +2509,8 @@ retry:
                         goto mismatch;
                 if (unlikely(d_unhashed(dentry)))
                         goto mismatch;
-                if (parent->d_flags & DCACHE_OP_COMPARE) {
-                        int tlen = dentry->d_name.len;
-                        const char *tname = dentry->d_name.name;
-                        if (parent->d_op->d_compare(parent, dentry, tlen, tname, name))
-                                goto mismatch;
-                } else {
-                        if (unlikely(dentry->d_name.len != len))
-                                goto mismatch;
-                        if (unlikely(dentry_cmp(dentry, str, len)))
-                                goto mismatch;
-                }
+                if (unlikely(!d_same_name(dentry, parent, name)))
+                        goto mismatch;
                 /* OK, it *is* a hashed match; return it */
                 spin_unlock(&dentry->d_lock);
                 dput(new);
@@ -2657,8 +2606,6 @@ EXPORT_SYMBOL(d_add);
 struct dentry *d_exact_alias(struct dentry *entry, struct inode *inode)
 {
         struct dentry *alias;
-        int len = entry->d_name.len;
-        const char *name = entry->d_name.name;
         unsigned int hash = entry->d_name.hash;
 
         spin_lock(&inode->i_lock);
@@ -2672,9 +2619,7 @@ struct dentry *d_exact_alias(struct dentry *entry, struct inode *inode)
                         continue;
                 if (alias->d_parent != entry->d_parent)
                         continue;
-                if (alias->d_name.len != len)
-                        continue;
-                if (dentry_cmp(alias, name, len))
+                if (!d_same_name(alias, entry->d_parent, &entry->d_name))
                         continue;
                 spin_lock(&alias->d_lock);
                 if (!d_unhashed(alias)) {