vfs: add find_inode_nowait() function

Add a new function find_inode_nowait() which is an even more general
version of ilookup5_nowait().  It is designed for callers which need
very fine grained control over when the function is allowed to block
or increment the inode's reference count.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 50 insertions, 0 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 4feb85cc125f..740cba79c2b9 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1284,6 +1284,56 @@ struct inode *ilookup(struct super_block *sb, unsigned long ino)
 }
 EXPORT_SYMBOL(ilookup);
 
+/**
+ * find_inode_nowait - find an inode in the inode cache
+ * @sb:         super block of file system to search
+ * @hashval:    hash value (usually inode number) to search for
+ * @match:      callback used for comparisons between inodes
+ * @data:       opaque data pointer to pass to @match
+ *
+ * Search for the inode specified by @hashval and @data in the inode
+ * cache, where the helper function @match will return 0 if the inode
+ * does not match, 1 if the inode does match, and -1 if the search
+ * should be stopped.  The @match function must be responsible for
+ * taking the i_lock spin_lock and checking i_state for an inode being
+ * freed or being initialized, and incrementing the reference count
+ * before returning 1.  It also must not sleep, since it is called with
+ * the inode_hash_lock spinlock held.
+ *
+ * This is a even more generalized version of ilookup5() when the
+ * function must never block --- find_inode() can block in
+ * __wait_on_freeing_inode() --- or when the caller can not increment
+ * the reference count because the resulting iput() might cause an
+ * inode eviction.  The tradeoff is that the @match funtion must be
+ * very carefully implemented.
+ */
+struct inode *find_inode_nowait(struct super_block *sb,
+                                unsigned long hashval,
+                                int (*match)(struct inode *, unsigned long,
+                                             void *),
+                                void *data)
+{
+        struct hlist_head *head = inode_hashtable + hash(sb, hashval);
+        struct inode *inode, *ret_inode = NULL;
+        int mval;
+
+        spin_lock(&inode_hash_lock);
+        hlist_for_each_entry(inode, head, i_hash) {
+                if (inode->i_sb != sb)
+                        continue;
+                mval = match(inode, hashval, data);
+                if (mval == 0)
+                        continue;
+                if (mval == 1)
+                        ret_inode = inode;
+                goto out;
+        }
+out:
+        spin_unlock(&inode_hash_lock);
+        return ret_inode;
+}
+EXPORT_SYMBOL(find_inode_nowait);
+
 int insert_inode_locked(struct inode *inode)
 {
         struct super_block *sb = inode->i_sb;