resource: ability to resize an allocated resource
Ram Pai [Wed, 6 Jul 2011 06:44:30 +0000 (23:44 -0700)]
Provides the ability to resize a resource that is already allocated.
This functionality is put in place to support reallocation needs of
pci resources.

Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/resource.c

index 798e2fa..3ff4017 100644 (file)
@@ -38,6 +38,14 @@ struct resource iomem_resource = {
 };
 EXPORT_SYMBOL(iomem_resource);
 
+/* constraints to be met while allocating resources */
+struct resource_constraint {
+       resource_size_t min, max, align;
+       resource_size_t (*alignf)(void *, const struct resource *,
+                       resource_size_t, resource_size_t);
+       void *alignf_data;
+};
+
 static DEFINE_RWLOCK(resource_lock);
 
 static void *r_next(struct seq_file *m, void *v, loff_t *pos)
@@ -384,16 +392,13 @@ static bool resource_contains(struct resource *res1, struct resource *res2)
 }
 
 /*
- * Find empty slot in the resource tree given range and alignment.
+ * Find empty slot in the resource tree with the given range and
+ * alignment constraints
  */
-static int find_resource(struct resource *root, struct resource *new,
-                        resource_size_t size, resource_size_t min,
-                        resource_size_t max, resource_size_t align,
-                        resource_size_t (*alignf)(void *,
-                                                  const struct resource *,
-                                                  resource_size_t,
-                                                  resource_size_t),
-                        void *alignf_data)
+static int __find_resource(struct resource *root, struct resource *old,
+                        struct resource *new,
+                        resource_size_t  size,
+                        struct resource_constraint *constraint)
 {
        struct resource *this = root->child;
        struct resource tmp = *new, avail, alloc;
@@ -404,25 +409,26 @@ static int find_resource(struct resource *root, struct resource *new,
         * Skip past an allocated resource that starts at 0, since the assignment
         * of this->start - 1 to tmp->end below would cause an underflow.
         */
-       if (this && this->start == 0) {
-               tmp.start = this->end + 1;
+       if (this && this->start == root->start) {
+               tmp.start = (this == old) ? old->start : this->end + 1;
                this = this->sibling;
        }
        for(;;) {
                if (this)
-                       tmp.end = this->start - 1;
+                       tmp.end = (this == old) ?  this->end : this->start - 1;
                else
                        tmp.end = root->end;
 
-               resource_clip(&tmp, min, max);
+               resource_clip(&tmp, constraint->min, constraint->max);
                arch_remove_reservations(&tmp);
 
                /* Check for overflow after ALIGN() */
                avail = *new;
-               avail.start = ALIGN(tmp.start, align);
+               avail.start = ALIGN(tmp.start, constraint->align);
                avail.end = tmp.end;
                if (avail.start >= tmp.start) {
-                       alloc.start = alignf(alignf_data, &avail, size, align);
+                       alloc.start = constraint->alignf(constraint->alignf_data, &avail,
+                                       size, constraint->align);
                        alloc.end = alloc.start + size - 1;
                        if (resource_contains(&avail, &alloc)) {
                                new->start = alloc.start;
@@ -432,14 +438,75 @@ static int find_resource(struct resource *root, struct resource *new,
                }
                if (!this)
                        break;
-               tmp.start = this->end + 1;
+               if (this != old)
+                       tmp.start = this->end + 1;
                this = this->sibling;
        }
        return -EBUSY;
 }
 
+/*
+ * Find empty slot in the resource tree given range and alignment.
+ */
+static int find_resource(struct resource *root, struct resource *new,
+                       resource_size_t size,
+                       struct resource_constraint  *constraint)
+{
+       return  __find_resource(root, NULL, new, size, constraint);
+}
+
 /**
- * allocate_resource - allocate empty slot in the resource tree given range & alignment
+ * reallocate_resource - allocate a slot in the resource tree given range & alignment.
+ *     The resource will be relocated if the new size cannot be reallocated in the
+ *     current location.
+ *
+ * @root: root resource descriptor
+ * @old:  resource descriptor desired by caller
+ * @newsize: new size of the resource descriptor
+ * @constraint: the size and alignment constraints to be met.
+ */
+int reallocate_resource(struct resource *root, struct resource *old,
+                       resource_size_t newsize,
+                       struct resource_constraint  *constraint)
+{
+       int err=0;
+       struct resource new = *old;
+       struct resource *conflict;
+
+       write_lock(&resource_lock);
+
+       if ((err = __find_resource(root, old, &new, newsize, constraint)))
+               goto out;
+
+       if (resource_contains(&new, old)) {
+               old->start = new.start;
+               old->end = new.end;
+               goto out;
+       }
+
+       if (old->child) {
+               err = -EBUSY;
+               goto out;
+       }
+
+       if (resource_contains(old, &new)) {
+               old->start = new.start;
+               old->end = new.end;
+       } else {
+               __release_resource(old);
+               *old = new;
+               conflict = __request_resource(root, old);
+               BUG_ON(conflict);
+       }
+out:
+       write_unlock(&resource_lock);
+       return err;
+}
+
+
+/**
+ * allocate_resource - allocate empty slot in the resource tree given range & alignment.
+ *     The resource will be reallocated with a new size if it was already allocated
  * @root: root resource descriptor
  * @new: resource descriptor desired by caller
  * @size: requested resource region size
@@ -459,12 +526,25 @@ int allocate_resource(struct resource *root, struct resource *new,
                      void *alignf_data)
 {
        int err;
+       struct resource_constraint constraint;
 
        if (!alignf)
                alignf = simple_align_resource;
 
+       constraint.min = min;
+       constraint.max = max;
+       constraint.align = align;
+       constraint.alignf = alignf;
+       constraint.alignf_data = alignf_data;
+
+       if ( new->parent ) {
+               /* resource is already allocated, try reallocating with
+                  the new constraints */
+               return reallocate_resource(root, new, size, &constraint);
+       }
+
        write_lock(&resource_lock);
-       err = find_resource(root, new, size, min, max, align, alignf, alignf_data);
+       err = find_resource(root, new, size, &constraint);
        if (err >= 0 && __request_resource(root, new))
                err = -EBUSY;
        write_unlock(&resource_lock);