kernfs: add an API to get kernfs node from inode number (ba16b284) · Commits · 戴 / test

fs/kernfs/dir.c

+57 −0

Original line number	Diff line number	Diff line
		@@ -508,6 +508,10 @@ void kernfs_put(struct kernfs_node *kn)
		struct kernfs_node *parent;
		struct kernfs_root *root;

		/*
		* kernfs_node is freed with ->count 0, kernfs_find_and_get_node_by_ino
		* depends on this to filter reused stale node
		*/
		if (!kn \|\| !atomic_dec_and_test(&kn->count))
		return;
		root = kernfs_root(kn);
		@@ -649,6 +653,11 @@ static struct kernfs_node __kernfs_new_node(struct kernfs_root root,
		kn->ino = ret;
		kn->generation = gen;

		/*
		* set ino first. This barrier is paired with atomic_inc_not_zero in
		* kernfs_find_and_get_node_by_ino
		*/
		smp_mb__before_atomic();
		atomic_set(&kn->count, 1);
		atomic_set(&kn->active, KN_DEACTIVATED_BIAS);
		RB_CLEAR_NODE(&kn->rb);
		@@ -680,6 +689,54 @@ struct kernfs_node kernfs_new_node(struct kernfs_node parent,
		return kn;
		}

		/*
		* kernfs_find_and_get_node_by_ino - get kernfs_node from inode number
		* @root: the kernfs root
		* @ino: inode number
		*
		* RETURNS:
		* NULL on failure. Return a kernfs node with reference counter incremented
		*/
		struct kernfs_node kernfs_find_and_get_node_by_ino(struct kernfs_root root,
		unsigned int ino)
		{
		struct kernfs_node *kn;

		rcu_read_lock();
		kn = idr_find(&root->ino_idr, ino);
		if (!kn)
		goto out;

		/*
		* Since kernfs_node is freed in RCU, it's possible an old node for ino
		* is freed, but reused before RCU grace period. But a freed node (see
		* kernfs_put) or an incompletedly initialized node (see
		* __kernfs_new_node) should have 'count' 0. We can use this fact to
		* filter out such node.
		*/
		if (!atomic_inc_not_zero(&kn->count)) {
		kn = NULL;
		goto out;
		}

		/*
		* The node could be a new node or a reused node. If it's a new node,
		* we are ok. If it's reused because of RCU (because of
		* SLAB_TYPESAFE_BY_RCU), the __kernfs_new_node always sets its 'ino'
		* before 'count'. So if 'count' is uptodate, 'ino' should be uptodate,
		* hence we can use 'ino' to filter stale node.
		*/
		if (kn->ino != ino)
		goto out;
		rcu_read_unlock();

		return kn;
		out:
		rcu_read_unlock();
		kernfs_put(kn);
		return NULL;
		}

		/**
		* kernfs_add_one - add kernfs_node to parent without warning
		* @kn: kernfs_node to be added

fs/kernfs/kernfs-internal.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -98,6 +98,8 @@ int kernfs_add_one(struct kernfs_node *kn);
		struct kernfs_node kernfs_new_node(struct kernfs_node parent,
		const char *name, umode_t mode,
		unsigned flags);
		struct kernfs_node kernfs_find_and_get_node_by_ino(struct kernfs_root root,
		unsigned int ino);

		/*
		* file.c

fs/kernfs/mount.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -330,7 +330,16 @@ struct super_block kernfs_pin_sb(struct kernfs_root root, const void *ns)

		void __init kernfs_init(void)
		{

		/*
		* the slab is freed in RCU context, so kernfs_find_and_get_node_by_ino
		* can access the slab lock free. This could introduce stale nodes,
		* please see how kernfs_find_and_get_node_by_ino filters out stale
		* nodes.
		*/
		kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
		sizeof(struct kernfs_node),
		0, SLAB_PANIC, NULL);
		0,
		SLAB_PANIC \| SLAB_TYPESAFE_BY_RCU,
		NULL);
		}

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