kexec: add helper to exlude a region from a set of memory ranges

Add a helper to exclude a region from a set of memory ranges.

Signed-off-by: Russell King <rmk@arm.linux.org.uk>
Reviewed-by: Pratyush Anand <panand@redhat.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

2 files changed, 76 insertions, 0 deletions

diff --git a/kexec/mem_regions.c b/kexec/mem_regions.c
index 7b4bcf3..b01a5c8 100644
--- a/kexec/mem_regions.c
+++ b/kexec/mem_regions.c
@@ -54,3 +54,75 @@ int mem_regions_add(struct memory_ranges *ranges, unsigned long long base,
 
 	return 0;
 }
+
+static void mem_regions_remove(struct memory_ranges *ranges, int index)
+{
+	int tail_entries;
+
+	/* we are assured to have at least one entry */
+	ranges->size -= 1;
+
+	/* if we have following entries, shuffle them down one place */
+	tail_entries = ranges->size - index;
+	if (tail_entries)
+		memmove(ranges->ranges + index, ranges->ranges + index + 1,
+			tail_entries * sizeof(*ranges->ranges));
+
+	/* zero the new tail entry */
+	memset(ranges->ranges + ranges->size, 0, sizeof(*ranges->ranges));
+}
+
+/**
+ * mem_regions_exclude() - excludes a memory region from a set of memory ranges
+ * @ranges: memory ranges to exclude the region from
+ * @range: memory range to exclude
+ *
+ * Exclude a memory region from a set of memory ranges.  We assume that
+ * the region to be excluded is either wholely located within one of the
+ * memory ranges, or not at all.
+ */
+int mem_regions_exclude(struct memory_ranges *ranges,
+			const struct memory_range *range)
+{
+	int i, ret;
+
+	for (i = 0; i < ranges->size; i++) {
+		struct memory_range *r = ranges->ranges + i;
+
+		/*
+		 * We assume that crash area is fully contained in
+		 * some larger memory area.
+		 */
+		if (r->start <= range->start && r->end >= range->end) {
+			if (r->start == range->start) {
+				if (r->end == range->end)
+					/* Remove this entry */
+					mem_regions_remove(ranges, i);
+				else
+					/* Shrink the start of this memory range */
+					r->start = range->end + 1;
+			} else if (r->end == range->end) {
+				/* Shrink the end of this memory range */
+				r->end = range->start - 1;
+			} else {
+				/*
+				 * Split this area into 2 smaller ones and
+				 * remove excluded range from between. First
+				 * create new entry for the remaining area.
+				 */
+				ret = mem_regions_add(ranges, range->end + 1,
+						      r->end - range->end, 0);
+				if (ret < 0)
+					return ret;
+
+				/*
+				 * Update this area to end before excluded
+				 * range.
+				 */
+				r->end = range->start - 1;
+				break;
+			}
+		}
+	}
+	return 0;
+}
diff --git a/kexec/mem_regions.h b/kexec/mem_regions.h
index da7b5e8..ae9e972 100644
--- a/kexec/mem_regions.h
+++ b/kexec/mem_regions.h
@@ -2,9 +2,13 @@
 #define MEM_REGIONS_H
 
 struct memory_ranges;
+struct memory_range;
 
 void mem_regions_sort(struct memory_ranges *ranges);
 
+int mem_regions_exclude(struct memory_ranges *ranges,
+			const struct memory_range *range);
+
 int mem_regions_add(struct memory_ranges *ranges, unsigned long long base,
                     unsigned long long length, int type);