3 files changed, 289 insertions, 1 deletions

diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
index c0ddfd29c5e5..70798407b9a2 100644
--- a/fs/btrfs/Makefile
+++ b/fs/btrfs/Makefile
@@ -8,6 +8,6 @@ btrfs-y += super.o ctree.o extent-tree.o print-tree.o root-tree.o dir-item.o \
            extent_io.o volumes.o async-thread.o ioctl.o locking.o orphan.o \
            export.o tree-log.o free-space-cache.o zlib.o lzo.o \
            compression.o delayed-ref.o relocation.o delayed-inode.o scrub.o \
-           reada.o backref.o
+           reada.o backref.o ulist.o
 
 btrfs-$(CONFIG_BTRFS_FS_POSIX_ACL) += acl.o
diff --git a/fs/btrfs/ulist.c b/fs/btrfs/ulist.c
new file mode 100644
index 000000000000..12f5147bd2b1
--- /dev/null
+++ b/fs/btrfs/ulist.c
@@ -0,0 +1,220 @@
+/*
+ * Copyright (C) 2011 STRATO AG
+ * written by Arne Jansen <sensille@gmx.net>
+ * Distributed under the GNU GPL license version 2.
+ */
+
+#include <linux/slab.h>
+#include <linux/module.h>
+#include "ulist.h"
+
+/*
+ * ulist is a generic data structure to hold a collection of unique u64
+ * values. The only operations it supports is adding to the list and
+ * enumerating it.
+ * It is possible to store an auxiliary value along with the key.
+ *
+ * The implementation is preliminary and can probably be sped up
+ * significantly. A first step would be to store the values in an rbtree
+ * as soon as ULIST_SIZE is exceeded.
+ *
+ * A sample usage for ulists is the enumeration of directed graphs without
+ * visiting a node twice. The pseudo-code could look like this:
+ *
+ * ulist = ulist_alloc();
+ * ulist_add(ulist, root);
+ * elem = NULL;
+ *
+ * while ((elem = ulist_next(ulist, elem)) {
+ *      for (all child nodes n in elem)
+ *              ulist_add(ulist, n);
+ *      do something useful with the node;
+ * }
+ * ulist_free(ulist);
+ *
+ * This assumes the graph nodes are adressable by u64. This stems from the
+ * usage for tree enumeration in btrfs, where the logical addresses are
+ * 64 bit.
+ *
+ * It is also useful for tree enumeration which could be done elegantly
+ * recursively, but is not possible due to kernel stack limitations. The
+ * loop would be similar to the above.
+ */
+
+/**
+ * ulist_init - freshly initialize a ulist
+ * @ulist:      the ulist to initialize
+ *
+ * Note: don't use this function to init an already used ulist, use
+ * ulist_reinit instead.
+ */
+void ulist_init(struct ulist *ulist)
+{
+        ulist->nnodes = 0;
+        ulist->nodes = ulist->int_nodes;
+        ulist->nodes_alloced = ULIST_SIZE;
+}
+EXPORT_SYMBOL(ulist_init);
+
+/**
+ * ulist_fini - free up additionally allocated memory for the ulist
+ * @ulist:      the ulist from which to free the additional memory
+ *
+ * This is useful in cases where the base 'struct ulist' has been statically
+ * allocated.
+ */
+void ulist_fini(struct ulist *ulist)
+{
+        /*
+         * The first ULIST_SIZE elements are stored inline in struct ulist.
+         * Only if more elements are alocated they need to be freed.
+         */
+        if (ulist->nodes_alloced > ULIST_SIZE)
+                kfree(ulist->nodes);
+        ulist->nodes_alloced = 0;       /* in case ulist_fini is called twice */
+}
+EXPORT_SYMBOL(ulist_fini);
+
+/**
+ * ulist_reinit - prepare a ulist for reuse
+ * @ulist:      ulist to be reused
+ *
+ * Free up all additional memory allocated for the list elements and reinit
+ * the ulist.
+ */
+void ulist_reinit(struct ulist *ulist)
+{
+        ulist_fini(ulist);
+        ulist_init(ulist);
+}
+EXPORT_SYMBOL(ulist_reinit);
+
+/**
+ * ulist_alloc - dynamically allocate a ulist
+ * @gfp_mask:   allocation flags to for base allocation
+ *
+ * The allocated ulist will be returned in an initialized state.
+ */
+struct ulist *ulist_alloc(unsigned long gfp_mask)
+{
+        struct ulist *ulist = kmalloc(sizeof(*ulist), gfp_mask);
+
+        if (!ulist)
+                return NULL;
+
+        ulist_init(ulist);
+
+        return ulist;
+}
+EXPORT_SYMBOL(ulist_alloc);
+
+/**
+ * ulist_free - free dynamically allocated ulist
+ * @ulist:      ulist to free
+ *
+ * It is not necessary to call ulist_fini before.
+ */
+void ulist_free(struct ulist *ulist)
+{
+        if (!ulist)
+                return;
+        ulist_fini(ulist);
+        kfree(ulist);
+}
+EXPORT_SYMBOL(ulist_free);
+
+/**
+ * ulist_add - add an element to the ulist
+ * @ulist:      ulist to add the element to
+ * @val:        value to add to ulist
+ * @aux:        auxiliary value to store along with val
+ * @gfp_mask:   flags to use for allocation
+ *
+ * Note: locking must be provided by the caller. In case of rwlocks write
+ *       locking is needed
+ *
+ * Add an element to a ulist. The @val will only be added if it doesn't
+ * already exist. If it is added, the auxiliary value @aux is stored along with
+ * it. In case @val already exists in the ulist, @aux is ignored, even if
+ * it differs from the already stored value.
+ *
+ * ulist_add returns 0 if @val already exists in ulist and 1 if @val has been
+ * inserted.
+ * In case of allocation failure -ENOMEM is returned and the ulist stays
+ * unaltered.
+ */
+int ulist_add(struct ulist *ulist, u64 val, unsigned long aux,
+              unsigned long gfp_mask)
+{
+        int i;
+
+        for (i = 0; i < ulist->nnodes; ++i) {
+                if (ulist->nodes[i].val == val)
+                        return 0;
+        }
+
+        if (ulist->nnodes >= ulist->nodes_alloced) {
+                u64 new_alloced = ulist->nodes_alloced + 128;
+                struct ulist_node *new_nodes;
+                void *old = NULL;
+
+                /*
+                 * if nodes_alloced == ULIST_SIZE no memory has been allocated
+                 * yet, so pass NULL to krealloc
+                 */
+                if (ulist->nodes_alloced > ULIST_SIZE)
+                        old = ulist->nodes;
+
+                new_nodes = krealloc(old, sizeof(*new_nodes) * new_alloced,
+                                     gfp_mask);
+                if (!new_nodes)
+                        return -ENOMEM;
+
+                if (!old)
+                        memcpy(new_nodes, ulist->int_nodes,
+                               sizeof(ulist->int_nodes));
+
+                ulist->nodes = new_nodes;
+                ulist->nodes_alloced = new_alloced;
+        }
+        ulist->nodes[ulist->nnodes].val = val;
+        ulist->nodes[ulist->nnodes].aux = aux;
+        ++ulist->nnodes;
+
+        return 1;
+}
+EXPORT_SYMBOL(ulist_add);
+
+/**
+ * ulist_next - iterate ulist
+ * @ulist:      ulist to iterate
+ * @prev:       previously returned element or %NULL to start iteration
+ *
+ * Note: locking must be provided by the caller. In case of rwlocks only read
+ *       locking is needed
+ *
+ * This function is used to iterate an ulist. The iteration is started with
+ * @prev = %NULL. It returns the next element from the ulist or %NULL when the
+ * end is reached. No guarantee is made with respect to the order in which
+ * the elements are returned. They might neither be returned in order of
+ * addition nor in ascending order.
+ * It is allowed to call ulist_add during an enumeration. Newly added items
+ * are guaranteed to show up in the running enumeration.
+ */
+struct ulist_node *ulist_next(struct ulist *ulist, struct ulist_node *prev)
+{
+        int next;
+
+        if (ulist->nnodes == 0)
+                return NULL;
+
+        if (!prev)
+                return &ulist->nodes[0];
+
+        next = (prev - ulist->nodes) + 1;
+        if (next < 0 || next >= ulist->nnodes)
+                return NULL;
+
+        return &ulist->nodes[next];
+}
+EXPORT_SYMBOL(ulist_next);
diff --git a/fs/btrfs/ulist.h b/fs/btrfs/ulist.h
new file mode 100644
index 000000000000..2e25dec58ec0
--- /dev/null
+++ b/fs/btrfs/ulist.h
@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2011 STRATO AG
+ * written by Arne Jansen <sensille@gmx.net>
+ * Distributed under the GNU GPL license version 2.
+ *
+ */
+
+#ifndef __ULIST__
+#define __ULIST__
+
+/*
+ * ulist is a generic data structure to hold a collection of unique u64
+ * values. The only operations it supports is adding to the list and
+ * enumerating it.
+ * It is possible to store an auxiliary value along with the key.
+ *
+ * The implementation is preliminary and can probably be sped up
+ * significantly. A first step would be to store the values in an rbtree
+ * as soon as ULIST_SIZE is exceeded.
+ */
+
+/*
+ * number of elements statically allocated inside struct ulist
+ */
+#define ULIST_SIZE 16
+
+/*
+ * element of the list
+ */
+struct ulist_node {
+        u64 val;                /* value to store */
+        unsigned long aux;      /* auxiliary value saved along with the val */
+};
+
+struct ulist {
+        /*
+         * number of elements stored in list
+         */
+        unsigned long nnodes;
+
+        /*
+         * number of nodes we already have room for
+         */
+        unsigned long nodes_alloced;
+
+        /*
+         * pointer to the array storing the elements. The first ULIST_SIZE
+         * elements are stored inline. In this case the it points to int_nodes.
+         * After exceeding ULIST_SIZE, dynamic memory is allocated.
+         */
+        struct ulist_node *nodes;
+
+        /*
+         * inline storage space for the first ULIST_SIZE entries
+         */
+        struct ulist_node int_nodes[ULIST_SIZE];
+};
+
+void ulist_init(struct ulist *ulist);
+void ulist_fini(struct ulist *ulist);
+void ulist_reinit(struct ulist *ulist);
+struct ulist *ulist_alloc(unsigned long gfp_mask);
+void ulist_free(struct ulist *ulist);
+int ulist_add(struct ulist *ulist, u64 val, unsigned long aux,
+              unsigned long gfp_mask);
+struct ulist_node *ulist_next(struct ulist *ulist, struct ulist_node *prev);
+
+#endif