* d_lookup - search for a dentry
* @parent: parent dentry
* @name: qstr of name we wish to find
+ * Returns: dentry, or NULL
*
- * Searches the children of the parent dentry for the name in question. If
- * the dentry is found its reference count is incremented and the dentry
- * is returned. The caller must use dput to free the entry when it has
- * finished using it. %NULL is returned on failure.
- *
- * __d_lookup is dcache_lock free. The hash list is protected using RCU.
- * Memory barriers are used while updating and doing lockless traversal.
- * To avoid races with d_move while rename is happening, d_lock is used.
- *
- * Overflows in memcmp(), while d_move, are avoided by keeping the length
- * and name pointer in one structure pointed by d_qstr.
- *
- * rcu_read_lock() and rcu_read_unlock() are used to disable preemption while
- * lookup is going on.
- *
- * The dentry unused LRU is not updated even if lookup finds the required dentry
- * in there. It is updated in places such as prune_dcache, shrink_dcache_sb,
- * select_parent and __dget_locked. This laziness saves lookup from dcache_lock
- * acquisition.
- *
- * d_lookup() is protected against the concurrent renames in some unrelated
- * directory using the seqlockt_t rename_lock.
+ * d_lookup searches the children of the parent dentry for the name in
+ * question. If the dentry is found its reference count is incremented and the
+ * dentry is returned. The caller must use dput to free the entry when it has
+ * finished using it. %NULL is returned if the dentry does not exist.
*/
-
struct dentry * d_lookup(struct dentry * parent, struct qstr * name)
{
struct dentry * dentry = NULL;
}
EXPORT_SYMBOL(d_lookup);
+/*
+ * __d_lookup - search for a dentry (racy)
+ * @parent: parent dentry
+ * @name: qstr of name we wish to find
+ * Returns: dentry, or NULL
+ *
+ * __d_lookup is like d_lookup, however it may (rarely) return a
+ * false-negative result due to unrelated rename activity.
+ *
+ * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
+ * however it must be used carefully, eg. with a following d_lookup in
+ * the case of failure.
+ *
+ * __d_lookup callers must be commented.
+ */
struct dentry * __d_lookup(struct dentry * parent, struct qstr * name)
{
unsigned int len = name->len;
struct hlist_node *node;
struct dentry *dentry;
+ /*
+ * The hash list is protected using RCU.
+ *
+ * Take d_lock when comparing a candidate dentry, to avoid races
+ * with d_move().
+ *
+ * It is possible that concurrent renames can mess up our list
+ * walk here and result in missing our dentry, resulting in the
+ * false-negative result. d_lookup() protects against concurrent
+ * renames using rename_lock seqlock.
+ *
+ * See Documentation/vfs/dcache-locking.txt for more details.
+ */
rcu_read_lock();
hlist_for_each_entry_rcu(dentry, node, head, d_hash) {
/*
* Recheck the dentry after taking the lock - d_move may have
- * changed things. Don't bother checking the hash because we're
- * about to compare the whole name anyway.
+ * changed things. Don't bother checking the hash because
+ * we're about to compare the whole name anyway.
*/
if (dentry->d_parent != parent)
goto next;
bool slash = false;
int error = 0;
- spin_lock(&vfsmount_lock);
+ br_read_lock(vfsmount_lock);
while (dentry != root->dentry || vfsmnt != root->mnt) {
struct dentry * parent;
if (!error && !slash)
error = prepend(buffer, buflen, "/", 1);
- spin_unlock(&vfsmount_lock);
+ br_read_unlock(vfsmount_lock);
return error;
global_root:
* __d_path - return the path of a dentry
* @path: the dentry/vfsmount to report
* @root: root vfsmnt/dentry (may be modified by this function)
- * @buffer: buffer to return value in
+ * @buf: buffer to return value in
* @buflen: buffer length
*
- * Convert a dentry into an ASCII path name. If the entry has been deleted
- * the string " (deleted)" is appended. Note that this is ambiguous.
+ * Convert a dentry into an ASCII path name.
*
* Returns a pointer into the buffer or an error code if the
* path was too long.
int error;
prepend(&res, &buflen, "\0", 1);
- if (d_unlinked(path->dentry)) {
- error = prepend(&res, &buflen, " (deleted)", 10);
- if (error)
- return ERR_PTR(error);
- }
-
error = prepend_path(path, root, &res, &buflen);
if (error)
return ERR_PTR(error);
return res;
}
+/*
+ * same as __d_path but appends "(deleted)" for unlinked files.
+ */
+static int path_with_deleted(const struct path *path, struct path *root,
+ char **buf, int *buflen)
+{
+ prepend(buf, buflen, "\0", 1);
+ if (d_unlinked(path->dentry)) {
+ int error = prepend(buf, buflen, " (deleted)", 10);
+ if (error)
+ return error;
+ }
+
+ return prepend_path(path, root, buf, buflen);
+}
+
+static int prepend_unreachable(char **buffer, int *buflen)
+{
+ return prepend(buffer, buflen, "(unreachable)", 13);
+}
+
/**
* d_path - return the path of a dentry
* @path: path to report
*/
char *d_path(const struct path *path, char *buf, int buflen)
{
- char *res;
+ char *res = buf + buflen;
struct path root;
struct path tmp;
+ int error;
/*
* We have various synthetic filesystems that never get mounted. On
get_fs_root(current->fs, &root);
spin_lock(&dcache_lock);
tmp = root;
- res = __d_path(path, &tmp, buf, buflen);
+ error = path_with_deleted(path, &tmp, &res, &buflen);
+ if (error)
+ res = ERR_PTR(error);
spin_unlock(&dcache_lock);
path_put(&root);
return res;
}
EXPORT_SYMBOL(d_path);
+/**
+ * d_path_with_unreachable - return the path of a dentry
+ * @path: path to report
+ * @buf: buffer to return value in
+ * @buflen: buffer length
+ *
+ * The difference from d_path() is that this prepends "(unreachable)"
+ * to paths which are unreachable from the current process' root.
+ */
+char *d_path_with_unreachable(const struct path *path, char *buf, int buflen)
+{
+ char *res = buf + buflen;
+ struct path root;
+ struct path tmp;
+ int error;
+
+ if (path->dentry->d_op && path->dentry->d_op->d_dname)
+ return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
+
+ get_fs_root(current->fs, &root);
+ spin_lock(&dcache_lock);
+ tmp = root;
+ error = path_with_deleted(path, &tmp, &res, &buflen);
+ if (!error && !path_equal(&tmp, &root))
+ error = prepend_unreachable(&res, &buflen);
+ spin_unlock(&dcache_lock);
+ path_put(&root);
+ if (error)
+ res = ERR_PTR(error);
+
+ return res;
+}
+
/*
* Helper function for dentry_operations.d_dname() members
*/
if (!d_unlinked(pwd.dentry)) {
unsigned long len;
struct path tmp = root;
- char * cwd;
+ char *cwd = page + PAGE_SIZE;
+ int buflen = PAGE_SIZE;
- cwd = __d_path(&pwd, &tmp, page, PAGE_SIZE);
+ prepend(&cwd, &buflen, "\0", 1);
+ error = prepend_path(&pwd, &tmp, &cwd, &buflen);
spin_unlock(&dcache_lock);
- error = PTR_ERR(cwd);
- if (IS_ERR(cwd))
+ if (error)
goto out;
+ /* Unreachable from current root */
+ if (!path_equal(&tmp, &root)) {
+ error = prepend_unreachable(&cwd, &buflen);
+ if (error)
+ goto out;
+ }
+
error = -ERANGE;
len = PAGE_SIZE + page - cwd;
if (len <= size) {
struct vfsmount *mnt = path1->mnt;
struct dentry *dentry = path1->dentry;
int res;
- spin_lock(&vfsmount_lock);
+
+ br_read_lock(vfsmount_lock);
if (mnt != path2->mnt) {
for (;;) {
if (mnt->mnt_parent == mnt) {
- spin_unlock(&vfsmount_lock);
+ br_read_unlock(vfsmount_lock);
return 0;
}
if (mnt->mnt_parent == path2->mnt)
dentry = mnt->mnt_mountpoint;
}
res = is_subdir(dentry, path2->dentry);
- spin_unlock(&vfsmount_lock);
+ br_read_unlock(vfsmount_lock);
return res;
}
EXPORT_SYMBOL(path_is_under);
projects / deliverable / linux.git / blobdiff