From f2300b433e152968a0fcabd79fb9d0f5fda6bca3 Mon Sep 17 00:00:00 2001
From: Kimplul <kimi.h.kuparinen@gmail.com>
Date: Thu, 23 Dec 2021 18:23:50 +0200
Subject: Added alloc_fixed_region

+ Not used at the moment anywhere, but should come in handy when
  emulating stuff like (s)brk and when mapping ELF stuff
---
 common/vmem.c        | 100 ++++++++++++++++++++++++++++++++++++++++-----------
 include/apos/utils.h |   2 ++
 2 files changed, 82 insertions(+), 20 deletions(-)

diff --git a/common/vmem.c b/common/vmem.c
index 3795d0b..70ef24e 100644
--- a/common/vmem.c
+++ b/common/vmem.c
@@ -177,6 +177,32 @@ static size_t po_align(size_t s)
 	return 0;
 }
 
+static struct sp_mem *sp_find_used_closest(struct sp_reg_root *r, vm_t start)
+{
+	struct sp_mem *closest = 0;
+	size_t md = (size_t)(-1);
+	struct sp_node *n = sp_root(r->used_regions);
+	while(n){
+		struct sp_mem *t = mem_container(n);
+		size_t d = ABS((ssize_t)start - (ssize_t)t->start);
+
+		if(d == 0) /* exact match */
+			return t;
+
+		if(d < md){ /* closest so far */
+			closest = t;
+			md = d;
+		}
+
+		if(start < t->start)
+			n = sp_left(n);
+		else
+			n = sp_right(n);
+	}
+
+	return closest;
+}
+
 /* should probably document this a bit better but in short, look for the "best"
  * free block, meaning one that is hopefully aligned so as to allow us to later
  * map it to higher order pages. If no block is found such that that is
@@ -211,27 +237,14 @@ static struct sp_mem *sp_find_free_best(struct sp_reg_root *r, size_t size, size
 	return quick_best;
 }
 
-/* apparently Linux doesn't necessarily give a shit about mmap hints, so I'll
- * just ignore them for now. Note that alloc_region should only be used when
- * mmap is called with MAP_ANON, all other situations should be handled in some
- * fs server */
-vm_t alloc_region(struct sp_reg_root *r,
-		size_t size, size_t *actual_size)
+static size_t sp_use_region(struct sp_reg_root *r, struct sp_mem *m,
+		size_t pages, size_t align)
 {
-	*actual_size = align_up(size, BASE_PAGE_SIZE);
-	size_t pages = __page(*actual_size);
-
-	/* find best fitting, alignment etc. */
-	size_t align = 0;
-	struct sp_mem *m = sp_find_free_best(r, pages, &align);
-	if(!m)
-		return 0;
-
 	sp_remove(&sp_root(r->free_regions), &m->sp_n);
 
 	vm_t pre_start = m->start;
 	vm_t pre_end = pre_start + align;
-
+	
 	vm_t start = pre_end;
 	vm_t end = start + pages;
 
@@ -243,8 +256,6 @@ vm_t alloc_region(struct sp_reg_root *r,
 		m->prev = n;
 		if(n->prev)
 			n->prev->next = n;
-
-		sp_free_insert_region(r, n);
 	}
 
 	if(post_start != post_end){
@@ -252,8 +263,6 @@ vm_t alloc_region(struct sp_reg_root *r,
 		m->next = n;
 		if(n->next)
 			n->next->prev = n;
-
-		sp_free_insert_region(r, n);
 	}
 
 	m->end = end;
@@ -263,6 +272,57 @@ vm_t alloc_region(struct sp_reg_root *r,
 	return __addr(start);
 }
 
+/* apparently Linux doesn't necessarily give a shit about mmap hints, so I'll
+ * just ignore them for now. Note that alloc_region should only be used when
+ * mmap is called with MAP_ANON, all other situations should be handled in some
+ * fs server */
+vm_t alloc_region(struct sp_reg_root *r,
+		size_t size, size_t *actual_size)
+{
+	*actual_size = align_up(size, BASE_PAGE_SIZE);
+	size_t pages = __page(*actual_size);
+
+	/* find best fitting, alignment etc. */
+	size_t align = 0;
+	struct sp_mem *m = sp_find_free_best(r, pages, &align);
+	if(!m)
+		return 0;
+
+	return sp_use_region(r, m, pages, align);
+}
+
+
+vm_t alloc_fixed_region(struct sp_reg_root *r,
+		vm_t start, size_t size, size_t *actual_size)
+{
+	*actual_size = align_up(size, BASE_PAGE_SIZE);
+	size_t pages = __page(*actual_size);
+	start = __page(start);
+
+	struct sp_mem *m = sp_find_used_closest(r, start);
+	if(!m)
+		return 0;
+
+	/* locate actual region where start is between the region start and end */
+	while(!((m->start <= start) && (start <= m->end))){
+		if(start < m->start)
+			m = m->next;
+		else
+			m = m->prev;
+	}
+
+	/* if region is already in use, forget it */
+	if(is_region_used(m->flags))
+		return 0;
+
+	/* region is too small */
+	if(start + pages > m->end)
+		return 0;
+
+	/* actually start marking region used */
+	return sp_use_region(r, m, pages, start - m->start);
+}
+
 static void __sp_try_coalesce_prev(struct sp_reg_root *r, struct sp_mem *m)
 {
 	while(m){
diff --git a/include/apos/utils.h b/include/apos/utils.h
index b973d49..f1e79fa 100644
--- a/include/apos/utils.h
+++ b/include/apos/utils.h
@@ -1,6 +1,8 @@
 #ifndef APOS_UTILS_H
 #define APOS_UTILS_H
 
+#define ABS(a) (a < 0 ? -a : a)
+
 #define MAX(a, b) ((a) >= (b) ? (a) : (b))
 #define MAX3(a, b, c) (MAX(a, b) >= MAX(b, c) ? MAX(a, b) : MAX(b, c))
 #define MAX4(a, b, c, d) (MAX3(a, b, c) >= MAX3(b, c, d) ? MAX3(a, b, c) : MAX3(b, c, d))
-- 
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