[RFC PATCH v5 23/26] util: Add iova_tree_alloc

["Eugenio Pérez" <eperezma@redhat.com>]

This iova tree function allows it to look for a hole in allocated
regions and return a totally new translation for a given translated
address.

It's usage is mainly to allow devices to access qemu address space,
remapping guest's one into a new iova space where qemu can add chunks of
addresses.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 include/qemu/iova-tree.h |  17 +++++
 util/iova-tree.c         | 139 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 156 insertions(+)

diff --git a/include/qemu/iova-tree.h b/include/qemu/iova-tree.h
index 8249edd764..33f9b2e13f 100644
--- a/include/qemu/iova-tree.h
+++ b/include/qemu/iova-tree.h
@@ -29,6 +29,7 @@
 #define  IOVA_OK           (0)
 #define  IOVA_ERR_INVALID  (-1) /* Invalid parameters */
 #define  IOVA_ERR_OVERLAP  (-2) /* IOVA range overlapped */
+#define  IOVA_ERR_NOMEM    (-3) /* Cannot allocate */
 
 typedef struct IOVATree IOVATree;
 typedef struct DMAMap {
@@ -119,6 +120,22 @@ const DMAMap *iova_tree_find_address(const IOVATree *tree, hwaddr iova);
  */
 void iova_tree_foreach(IOVATree *tree, iova_tree_iterator iterator);
 
+/**
+ * iova_tree_alloc:
+ *
+ * @tree: the iova tree to allocate from
+ * @map: the new map (as translated addr & size) to allocate in iova region
+ * @iova_begin: the minimum address of the allocation
+ * @iova_end: the maximum addressable direction of the allocation
+ *
+ * Allocates a new region of a given size, between iova_min and iova_max.
+ *
+ * Return: Same as iova_tree_insert, but cannot overlap and can be out of
+ * free contiguous range. Caller can get the assigned iova in map->iova.
+ */
+int iova_tree_alloc(IOVATree *tree, DMAMap *map, hwaddr iova_begin,
+                    hwaddr iova_end);
+
 /**
  * iova_tree_destroy:
  *
diff --git a/util/iova-tree.c b/util/iova-tree.c
index 23ea35b7a4..27c921c4e2 100644
--- a/util/iova-tree.c
+++ b/util/iova-tree.c
@@ -16,6 +16,36 @@ struct IOVATree {
     GTree *tree;
 };
 
+/* Args to pass to iova_tree_alloc foreach function. */
+struct IOVATreeAllocArgs {
+    /* Size of the desired allocation */
+    size_t new_size;
+
+    /* The minimum address allowed in the allocation */
+    hwaddr iova_begin;
+
+    /* The last addressable allowed in the allocation */
+    hwaddr iova_last;
+
+    /* Previously-to-last iterated map, can be NULL in the first node */
+    const DMAMap *hole_left;
+
+    /* Last iterated map */
+    const DMAMap *hole_right;
+};
+
+/**
+ * Iterate args to tne next hole
+ *
+ * @args  The alloc arguments
+ * @next  The next mapping in the tree. Can be NULL to signal the last one
+ */
+static void iova_tree_alloc_args_iterate(struct IOVATreeAllocArgs *args,
+                                         const DMAMap *next) {
+    args->hole_left = args->hole_right;
+    args->hole_right = next;
+}
+
 static int iova_tree_compare(gconstpointer a, gconstpointer b, gpointer data)
 {
     const DMAMap *m1 = a, *m2 = b;
@@ -107,6 +137,115 @@ int iova_tree_remove(IOVATree *tree, const DMAMap *map)
     return IOVA_OK;
 }
 
+/**
+ * Try to accomodate a map of size ret->size in a hole between
+ * max(end(hole_left), iova_start).
+ *
+ * @args Arguments to allocation
+ */
+static bool iova_tree_alloc_map_in_hole(const struct IOVATreeAllocArgs *args)
+{
+    const DMAMap *left = args->hole_left, *right = args->hole_right;
+    uint64_t hole_start, hole_last;
+
+    if (right && right->iova + right->size < args->iova_begin) {
+        return false;
+    }
+
+    if (left && left->iova > args->iova_last) {
+        return false;
+    }
+
+    hole_start = MAX(left ? left->iova + left->size + 1 : 0, args->iova_begin);
+    hole_last = MIN(right ? right->iova : HWADDR_MAX, args->iova_last);
+
+    if (hole_last - hole_start > args->new_size) {
+        /* We found a valid hole. */
+        return true;
+    }
+
+    /* Keep iterating */
+    return false;
+}
+
+/**
+ * Foreach dma node in the tree, compare if there is a hole wit its previous
+ * node (or minimum iova address allowed) and the node.
+ *
+ * @key   Node iterating
+ * @value Node iterating
+ * @pargs Struct to communicate with the outside world
+ *
+ * Return: false to keep iterating, true if needs break.
+ */
+static gboolean iova_tree_alloc_traverse(gpointer key, gpointer value,
+                                         gpointer pargs)
+{
+    struct IOVATreeAllocArgs *args = pargs;
+    DMAMap *node = value;
+
+    assert(key == value);
+
+    iova_tree_alloc_args_iterate(args, node);
+    if (args->hole_left && args->hole_left->iova > args->iova_last) {
+        return true;
+    }
+
+    if (iova_tree_alloc_map_in_hole(args)) {
+        return true;
+    }
+
+    return false;
+}
+
+int iova_tree_alloc(IOVATree *tree, DMAMap *map, hwaddr iova_begin,
+                    hwaddr iova_last)
+{
+    struct IOVATreeAllocArgs args = {
+        .new_size = map->size,
+        .iova_begin = iova_begin,
+        .iova_last = iova_last,
+    };
+
+    if (iova_begin == 0) {
+        /* Some devices does not like addr 0 */
+        iova_begin += qemu_real_host_page_size;
+    }
+
+    assert(iova_begin < iova_last);
+
+    /*
+     * Find a valid hole for the mapping
+     *
+     * Assuming low iova_begin, so no need to do a binary search to
+     * locate the first node.
+     *
+     * TODO: We can improve the search speed if we save the beginning and the
+     * end of holes, so we don't iterate over the previous saved ones.
+     *
+     * TODO: Replace all this with g_tree_node_first/next/last when available
+     * (from glib since 2.68). To do it with g_tree_foreach complicates the
+     * code a lot.
+     *
+     */
+    g_tree_foreach(tree->tree, iova_tree_alloc_traverse, &args);
+    if (!iova_tree_alloc_map_in_hole(&args)) {
+        /*
+         * 2nd try: Last iteration left args->right as the last DMAMap. But
+         * (right, end) hole needs to be checked too
+         */
+        iova_tree_alloc_args_iterate(&args, NULL);
+        if (!iova_tree_alloc_map_in_hole(&args)) {
+            return IOVA_ERR_NOMEM;
+        }
+    }
+
+    map->iova = MAX(iova_begin,
+                    args.hole_left ?
+                    args.hole_left->iova + args.hole_left->size + 1 : 0);
+    return iova_tree_insert(tree, map);
+}
+
 void iova_tree_destroy(IOVATree *tree)
 {
     g_tree_destroy(tree->tree);
-- 
2.27.0