[Devel] [PATCH RHEL7 COMMIT] ms/vfs: add find_inode_nowait() function

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-123.1.2-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-123.1.2.vz7.5.18
------>
commit c7ca151bbdf31676803eefca3110c71ced672998
Author: Dmitry Monakhov <dmonakhov at openvz.org>
Date:   Fri Jun 26 15:09:53 2015 +0400

    ms/vfs: add find_inode_nowait() function
    
    ML-commit: fe032c422c5ba562ba9c2d316f55e258e03259c6 Mon Sep 17 00:00:00 2001
    
    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 at mit.edu>
    Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
    Signed-off-by: Dmitry Monakhov <dmonakhov at openvz.org>
---
 fs/inode.c         | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h |  5 +++++
 2 files changed, 55 insertions(+)

diff --git a/fs/inode.c b/fs/inode.c
index 5d73316..297951b 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1298,6 +1298,56 @@ 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;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a7084f1..a342e63 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2573,6 +2573,11 @@ extern struct inode *ilookup(struct super_block *sb, unsigned long ino);
 
 extern struct inode * iget5_locked(struct super_block *, unsigned long, int (*test)(struct inode *, void *), int (*set)(struct inode *, void *), void *);
 extern struct inode * iget_locked(struct super_block *, unsigned long);
+extern struct inode *find_inode_nowait(struct super_block *,
+				       unsigned long,
+				       int (*match)(struct inode *,
+						    unsigned long, void *),
+				       void *data);
 extern int insert_inode_locked4(struct inode *, unsigned long, int (*test)(struct inode *, void *), void *);
 extern int insert_inode_locked(struct inode *);
 #ifdef CONFIG_DEBUG_LOCK_ALLOC