* Compare 2 name strings, return 0 if they match, otherwise non-zero.
* The strings are both count bytes long, and count is non-zero.
*/
-static inline int dentry_cmp(const unsigned char *cs, size_t scount,
- const unsigned char *ct, size_t tcount)
-{
#ifdef CONFIG_DCACHE_WORD_ACCESS
- unsigned long a,b,mask;
- if (unlikely(scount != tcount))
- return 1;
+#include <asm/word-at-a-time.h>
+/*
+ * NOTE! 'cs' and 'scount' come from a dentry, so it has a
+ * aligned allocation for this particular component. We don't
+ * strictly need the load_unaligned_zeropad() safety, but it
+ * doesn't hurt either.
+ *
+ * In contrast, 'ct' and 'tcount' can be from a pathname, and do
+ * need the careful unaligned handling.
+ */
+static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
+{
+ unsigned long a,b,mask;
for (;;) {
a = *(unsigned long *)cs;
- b = *(unsigned long *)ct;
+ b = load_unaligned_zeropad(ct);
if (tcount < sizeof(unsigned long))
break;
if (unlikely(a != b))
}
mask = ~(~0ul << tcount*8);
return unlikely(!!((a ^ b) & mask));
+}
+
#else
- if (scount != tcount)
- return 1;
+static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
+{
do {
if (*cs != *ct)
return 1;
tcount--;
} while (tcount);
return 0;
+}
+
#endif
+
+static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
+{
+ /*
+ * Be careful about RCU walk racing with rename:
+ * use ACCESS_ONCE to fetch the name pointer.
+ *
+ * NOTE! Even if a rename will mean that the length
+ * was not loaded atomically, we don't care. The
+ * RCU walk will check the sequence count eventually,
+ * and catch it. And we won't overrun the buffer,
+ * because we're reading the name pointer atomically,
+ * and a dentry name is guaranteed to be properly
+ * terminated with a NUL byte.
+ *
+ * End result: even if 'len' is wrong, we'll exit
+ * early because the data cannot match (there can
+ * be no NUL in the ct/tcount data)
+ */
+ return dentry_string_cmp(ACCESS_ONCE(dentry->d_name.name), ct, tcount);
}
static void __d_free(struct rcu_head *head)
}
list_for_each_entry(alias, &inode->i_dentry, d_alias) {
- struct qstr *qstr = &alias->d_name;
-
/*
* Don't need alias->d_lock here, because aliases with
* d_parent == entry->d_parent are not subject to name or
* parent changes, because the parent inode i_mutex is held.
*/
- if (qstr->hash != hash)
+ if (alias->d_name.hash != hash)
continue;
if (alias->d_parent != entry->d_parent)
continue;
- if (dentry_cmp(qstr->name, qstr->len, name, len))
+ if (alias->d_name.len != len)
+ continue;
+ if (dentry_cmp(alias, name, len))
continue;
__dget(alias);
return alias;
struct dentry *res = NULL;
if (root_inode) {
- static const struct qstr name = { .name = "/", .len = 1 };
+ static const struct qstr name = QSTR_INIT("/", 1);
res = __d_alloc(root_inode->i_sb, &name);
if (res)
}
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, length and inode 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 inode *inode,
+ struct dentry *dentry,
+ unsigned int seq,
+ const struct qstr *name)
+{
+ int tlen = dentry->d_name.len;
+ const char *tname = dentry->d_name.name;
+ struct inode *i = dentry->d_inode;
+
+ if (read_seqcount_retry(&dentry->d_seq, seq)) {
+ cpu_relax();
+ return D_COMP_SEQRETRY;
+ }
+ if (parent->d_op->d_compare(parent, inode,
+ dentry, i,
+ tlen, tname, name))
+ return D_COMP_NOMATCH;
+ return D_COMP_OK;
+}
+
/**
* __d_lookup_rcu - search for a dentry (racy, store-free)
* @parent: parent dentry
* the returned dentry, so long as its parent's seqlock is checked after the
* child is looked up. Thus, an interlocking stepping of sequence lock checks
* is formed, giving integrity down the path walk.
+ *
+ * NOTE! The caller *has* to check the resulting dentry against the sequence
+ * number we've returned before using any of the resulting dentry state!
*/
struct dentry *__d_lookup_rcu(const struct dentry *parent,
const struct qstr *name,
- unsigned *seqp, struct inode **inode)
+ unsigned *seqp, struct inode *inode)
{
- unsigned int len = name->len;
- unsigned int hash = name->hash;
+ u64 hashlen = name->hash_len;
const unsigned char *str = name->name;
- struct hlist_bl_head *b = d_hash(parent, hash);
+ struct hlist_bl_head *b = d_hash(parent, hashlen_hash(hashlen));
struct hlist_bl_node *node;
struct dentry *dentry;
*/
hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
unsigned seq;
- struct inode *i;
- const char *tname;
- int tlen;
-
- if (dentry->d_name.hash != hash)
- continue;
seqretry:
- seq = read_seqcount_begin(&dentry->d_seq);
- if (dentry->d_parent != parent)
- continue;
- if (d_unhashed(dentry))
- continue;
- tlen = dentry->d_name.len;
- tname = dentry->d_name.name;
- i = dentry->d_inode;
- prefetch(tname);
/*
- * This seqcount check is required to ensure name and
- * len are loaded atomically, so as not to walk off the
- * edge of memory when walking. If we could load this
- * atomically some other way, we could drop this check.
+ * The dentry sequence count protects us from concurrent
+ * renames, and thus protects inode, parent and name fields.
+ *
+ * The caller must perform a seqcount check in order
+ * to do anything useful with the returned dentry,
+ * including using the 'd_inode' pointer.
+ *
+ * NOTE! We do a "raw" seqcount_begin here. That means that
+ * we don't wait for the sequence count to stabilize if it
+ * is in the middle of a sequence change. If we do the slow
+ * 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.
*/
- if (read_seqcount_retry(&dentry->d_seq, seq))
- goto seqretry;
+ seq = raw_seqcount_begin(&dentry->d_seq);
+ if (dentry->d_parent != parent)
+ continue;
+ *seqp = seq;
+
if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
- if (parent->d_op->d_compare(parent, *inode,
- dentry, i,
- tlen, tname, name))
+ if (dentry->d_name.hash != hashlen_hash(hashlen))
continue;
- } else {
- if (dentry_cmp(tname, tlen, str, len))
+ switch (slow_dentry_cmp(parent, inode, dentry, seq, name)) {
+ case D_COMP_OK:
+ return dentry;
+ case D_COMP_NOMATCH:
continue;
+ default:
+ goto seqretry;
+ }
}
- /*
- * No extra seqcount check is required after the name
- * compare. The caller must perform a seqcount check in
- * order to do anything useful with the returned dentry
- * anyway.
- */
- *seqp = seq;
- *inode = i;
- return dentry;
+
+ if (dentry->d_name.hash_len != hashlen)
+ continue;
+ if (!dentry_cmp(dentry, str, hashlen_len(hashlen)))
+ return dentry;
}
return NULL;
}
rcu_read_lock();
hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
- const char *tname;
- int tlen;
if (dentry->d_name.hash != hash)
continue;
* It is safe to compare names since d_move() cannot
* change the qstr (protected by d_lock).
*/
- tlen = dentry->d_name.len;
- tname = dentry->d_name.name;
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, parent->d_inode,
dentry, dentry->d_inode,
tlen, tname, name))
goto next;
} else {
- if (dentry_cmp(tname, tlen, str, len))
+ if (dentry->d_name.len != len)
+ goto next;
+ if (dentry_cmp(dentry, str, len))
goto next;
}
projects / linux-2.6-block.git / blobdiff