[Devel] [PATCH RH7 v2] cgroup: add export_operations to cgroup super block

[Andrey Zhadchenko]

criu uses fhandle from fdinfo to dump inotify objects. cgroup super block has
no export operations, but .encode_fh and .fh_to_dentry are needed for
inotify_fdinfo function and open_by_handle_at syscall in order to correctly
open files located on cgroupfs by fhandle.
Add hash table as a storage for inodes with exported fhandle.

https://jira.sw.ru/browse/PSBM-105889
Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
---
 kernel/cgroup.c | 112 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 111 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 9fdba79..a459c56 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -62,6 +62,7 @@
 #include <linux/kthread.h>
 #include <linux/ve.h>
 #include <linux/stacktrace.h>
+#include <linux/exportfs.h>
 
 #include <linux/atomic.h>
 
@@ -1390,9 +1391,117 @@ out:
 }
 #endif
 
+/*
+ * hashtable for inodes that have exported fhandles.
+ * When we export fhandle, we add it's inode into
+ * hashtable so we can find it fast
+ */
+
+#define CGROUP_INODE_HASH_BITS 10
+static DEFINE_HASHTABLE(cgroup_inode_table, CGROUP_INODE_HASH_BITS);
+static DEFINE_SPINLOCK(cgroup_inode_table_lock);
+
+struct cg_inode_hitem {
+	struct inode *inode;
+	struct hlist_node hlist;
+};
+
+static inline unsigned long cgroup_inode_get_hash(unsigned int i_ino)
+{
+	return hash_32(i_ino, CGROUP_INODE_HASH_BITS);
+}
+
+static struct cg_inode_hitem *cgroup_inode_hash_find(unsigned int i_ino)
+{
+	struct cg_inode_hitem *i;
+	struct hlist_head *head = cgroup_inode_table
+		+ cgroup_inode_get_hash(i_ino);
+	struct cg_inode_hitem *found = 0;
+
+	spin_lock(&cgroup_inode_table_lock);
+	hlist_for_each_entry(i, head, hlist) {
+		if (i->inode->i_ino == i_ino) {
+			found = i;
+			break;
+		}
+	}
+	spin_unlock(&cgroup_inode_table_lock);
+
+	return found;
+}
+
+static struct dentry *cgroup_fh_to_dentry(struct super_block *sb,
+		struct fid *fid, int fh_len, int fh_type)
+{
+	struct cg_inode_hitem *item;
+	struct dentry *dentry = ERR_PTR(-ENOENT);
+
+	if (fh_len < 1)
+		return NULL;
+
+	item = cgroup_inode_hash_find(fid->raw[0]);
+	if (item)
+		dentry = d_find_alias(item->inode);
+
+	return dentry;
+}
+
+static int cgroup_encode_fh(struct inode *inode, __u32 *fh, int *len,
+				struct inode *parent)
+{
+	struct hlist_head *head = cgroup_inode_table
+		+ cgroup_inode_get_hash(inode->i_ino);
+	struct cg_inode_hitem *item;
+
+	if (*len < 1) {
+		*len = 1;
+		return FILEID_INVALID;
+	}
+
+	if (cgroup_inode_hash_find(inode->i_ino) == 0) {
+		item = kmalloc(sizeof(struct cg_inode_hitem),
+			GFP_KERNEL);
+		/*
+		 * encode_fh is expected to return 255 (FILEID_INVALID)
+		 * in case of failure. We can't return ENOMEM, so
+		 * return FILEID_INVALID at least
+		 */
+		if (!item)
+			return FILEID_INVALID;
+		item->inode = inode;
+
+		spin_lock(&cgroup_inode_table_lock);
+		hlist_add_head(&item->hlist, head);
+		spin_unlock(&cgroup_inode_table_lock);
+	}
+
+	fh[0] = inode->i_ino;
+	*len = 1;
+	return 1;
+}
+
+static const struct export_operations cgroup_export_ops = {
+	.encode_fh      = cgroup_encode_fh,
+	.fh_to_dentry	= cgroup_fh_to_dentry,
+};
+
+static int cgroup_delete_inode(struct inode *inode)
+{
+	struct cg_inode_hitem *item = cgroup_inode_hash_find(inode->i_ino);
+	if (item) {
+		spin_lock(&cgroup_inode_table_lock);
+		hlist_del(&item->hlist);
+		spin_unlock(&cgroup_inode_table_lock);
+
+		kfree(item);
+	}
+
+	return generic_delete_inode(inode);
+}
+
 static const struct super_operations cgroup_ops = {
 	.statfs = simple_statfs,
-	.drop_inode = generic_delete_inode,
+	.drop_inode = cgroup_delete_inode,
 	.show_options = cgroup_show_options,
 #ifdef CONFIG_VE
 	.show_path = cgroup_show_path,
@@ -1539,6 +1648,7 @@ static int cgroup_set_super(struct super_block *sb, void *data)
 	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
 	sb->s_magic = CGROUP_SUPER_MAGIC;
 	sb->s_op = &cgroup_ops;
+	sb->s_export_op = &cgroup_export_ops;
 
 	return 0;
 }
-- 
1.8.3.1