From d1a5d76b1c16ac4f2e386d90926fbce50df2efbd Mon Sep 17 00:00:00 2001
From: Matthew Sotoudeh <matthew@masot.net>
Date: Sat, 18 May 2024 15:55:38 -0700
Subject: more info on reservation

---
 imc/checker.c             |  2 +-
 magic_buddy/magic_buddy.c |  8 ++++++--
 magic_buddy/magic_buddy.h | 10 +++++++++-
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/imc/checker.c b/imc/checker.c
index a7f62ff..91cdfa8 100644
--- a/imc/checker.c
+++ b/imc/checker.c
@@ -51,7 +51,7 @@ void check_main() {
         verbose("Reserving %p -- %p\n", redzone_start, redzone_end);
         assert(reserve(redzone_start,
                        (uint8_t*)redzone_end - (uint8_t*)redzone_start,
-                       curr_buddy));
+                       0, 0, curr_buddy));
     }
 
     size_t size_options[] = {1, 128, 1024, 5, 167, 10500};
diff --git a/magic_buddy/magic_buddy.c b/magic_buddy/magic_buddy.c
index da18d4a..89daaa4 100644
--- a/magic_buddy/magic_buddy.c
+++ b/magic_buddy/magic_buddy.c
@@ -148,7 +148,8 @@ static struct free_block *rhs_child_of(struct free_block *block, size_t logsize,
 // NOTE: this method is perhaps more complicated than it needs to be because we
 // take great pains to avoid writing to the region that is being reserved
 // (e.g., in case it is device MMIO).
-int reserve(void *start, size_t size, struct buddy *state) {
+int reserve(void *start, size_t size, void **out_start, size_t *out_size,
+            struct buddy *state) {
     // (1) find the first free block to the left of start
     uint8_t *base = state->base;
     size_t virtual_start = (uint8_t*)start - base;
@@ -169,7 +170,8 @@ int reserve(void *start, size_t size, struct buddy *state) {
     int needs_zero = 1;
     size_t min_logsize = size2log(sizeof(struct free_block), 1);
     pop(block);
-    for (size_t logsize = block->logsize; logsize > min_logsize;) {
+    size_t logsize = block->logsize;
+    while (logsize > min_logsize) {
         struct free_block *rhs_child = rhs_child_of(block, logsize, state);
         if ((void*)rhs_child <= start) {        // move right
             block = rhs_child;
@@ -183,6 +185,8 @@ int reserve(void *start, size_t size, struct buddy *state) {
         }
     }
     if (needs_zero) memset(block, 0, sizeof(struct free_block));
+    if (out_start)  *out_start = block;
+    if (out_size)   *out_size = logsize;
     return 1;
 }
 
diff --git a/magic_buddy/magic_buddy.h b/magic_buddy/magic_buddy.h
index 167397b..3b5e8d0 100644
--- a/magic_buddy/magic_buddy.h
+++ b/magic_buddy/magic_buddy.h
@@ -42,10 +42,18 @@ void *reallocate(void *old, size_t new_size, size_t old_size,
                  struct buddy *state);
 
 // Attempts to reserve a range [@start,@start+@size).
+//
 // Returns 1 if success, 0 otherwise.
+//
 // Whenever possible, we avoid writing anything into the reserved region.
+//
+// If the reservation succeeds, and @out_start (@out_size) is negative, it puts
+// the start (size) of the actually reserved region into *@out_start
+// (*@out_size). These can be passed into liberate(...) later to unreserve.
+//
 // O(1)
-int reserve(void *start, size_t size, struct buddy *state);
+int reserve(void *start, size_t size, void **out_start, size_t *out_size,
+            struct buddy *state);
 
 // Update @state to assume the memory pool has been copied to
 // [@new_base,@new_base+@new_size)
-- 
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