[PATCH v3 2/3] resource: Add release_mem_region_adjustable()

[Toshi Kani]

Added release_mem_region_adjustable(), which releases a requested
region from a currently busy memory resource.  This interface
adjusts the matched memory resource accordingly even if the
requested region does not match exactly but still fits into.

This new interface is intended for memory hot-delete.  During
bootup, memory resources are inserted from the boot descriptor
table, such as EFI Memory Table and e820.  Each memory resource
entry usually covers the whole contigous memory range.  Memory
hot-delete request, on the other hand, may target to a particular
range of memory resource, and its size can be much smaller than
the whole contiguous memory.  Since the existing release interfaces
like __release_region() require a requested region to be exactly
matched to a resource entry, they do not allow a partial resource
to be released.

This new interface is restrictive (i.e. release under certain
conditions), which is consistent with other release interfaces,
__release_region() and __release_resource().  Additional release
conditions, such as an overlapping region to a resource entry,
can be supported after they are confirmed as valid cases.

There is no change to the existing interfaces since their restriction
is valid for I/O resources.

Signed-off-by: Toshi Kani <toshi.kani@xxxxxx>
Reviewed-by : Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
---
 include/linux/ioport.h |    4 ++
 kernel/resource.c      |  100 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 104 insertions(+)

diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index 85ac9b9b..961d4dc 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -192,6 +192,10 @@ extern struct resource * __request_region(struct resource *,
 extern int __check_region(struct resource *, resource_size_t, resource_size_t);
 extern void __release_region(struct resource *, resource_size_t,
 				resource_size_t);
+#ifdef CONFIG_MEMORY_HOTPLUG
+extern int release_mem_region_adjustable(struct resource *, resource_size_t,
+				resource_size_t);
+#endif
 
 static inline int __deprecated check_region(resource_size_t s,
 						resource_size_t n)
diff --git a/kernel/resource.c b/kernel/resource.c
index ae246f9..08791c8 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1021,6 +1021,106 @@ void __release_region(struct resource *parent, resource_size_t start,
 }
 EXPORT_SYMBOL(__release_region);
 
+#ifdef CONFIG_MEMORY_HOTPLUG
+/**
+ * release_mem_region_adjustable - release a previously reserved memory region
+ * @parent: parent resource descriptor
+ * @start: resource start address
+ * @size: resource region size
+ *
+ * This interface is intended for memory hot-delete.  The requested region
+ * is released from a currently busy memory resource.  The requested region
+ * must either match exactly or fit into a single busy resource entry.  In
+ * the latter case, the remaining resource is adjusted accordingly.
+ * Existing children of the busy memory resource must be immutable in the
+ * request.
+ *
+ * Note:
+ * - Additional release conditions, such as overlapping region, can be
+ *   supported after they are confirmed as valid cases.
+ * - When a busy memory resource gets split into two entries, the code
+ *   assumes that all children remain in the lower address entry for
+ *   simplicity.  Enhance this logic when necessary.
+ */
+int release_mem_region_adjustable(struct resource *parent,
+			resource_size_t start, resource_size_t size)
+{
+	struct resource **p;
+	struct resource *res, *new;
+	resource_size_t end;
+	int ret = -EINVAL;
+
+	end = start + size - 1;
+	if ((start < parent->start) || (end > parent->end))
+		return ret;
+
+	p = &parent->child;
+	write_lock(&resource_lock);
+
+	while ((res = *p)) {
+		if (res->start >= end)
+			break;
+
+		/* look for the next resource if it does not fit into */
+		if (res->start > start || res->end < end) {
+			p = &res->sibling;
+			continue;
+		}
+
+		if (!(res->flags & IORESOURCE_MEM))
+			break;
+
+		if (!(res->flags & IORESOURCE_BUSY)) {
+			p = &res->child;
+			continue;
+		}
+
+		/* found the target resource; let's adjust accordingly */
+		if (res->start == start && res->end == end) {
+			/* free the whole entry */
+			*p = res->sibling;
+			kfree(res);
+			ret = 0;
+		} else if (res->start == start && res->end != end) {
+			/* adjust the start */
+			ret = __adjust_resource(res, end + 1,
+						res->end - end);
+		} else if (res->start != start && res->end == end) {
+			/* adjust the end */
+			ret = __adjust_resource(res, res->start,
+						start - res->start);
+		} else {
+			/* split into two entries */
+			new = kzalloc(sizeof(struct resource), GFP_KERNEL);
+			if (!new) {
+				ret = -ENOMEM;
+				break;
+			}
+			new->name = res->name;
+			new->start = end + 1;
+			new->end = res->end;
+			new->flags = res->flags;
+			new->parent = res->parent;
+			new->sibling = res->sibling;
+			new->child = NULL;
+
+			ret = __adjust_resource(res, res->start,
+						start - res->start);
+			if (ret) {
+				kfree(new);
+				break;
+			}
+			res->sibling = new;
+		}
+
+		break;
+	}
+
+	write_unlock(&resource_lock);
+	return ret;
+}
+#endif	/* CONFIG_MEMORY_HOTPLUG */
+
 /*
  * Managed region resource
  */
--
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