Make vma::insert find unmapped_areas of vma_start == 0.

This code is inefficient, it doesn't guarantee to find an unmapped area if one exists, and it only works for crange.

Make vma::insert find unmapped_areas of vma_start == 0.
a1c5a19c · Silas Boyd-Wickizer · 931c2709 · a1c5a19c · a1c5a19c · a1c5a19c
--- a/include/vm.hh
+++ b/include/vm.hh
@@ -88,7 +88,7 @@ struct vmap {

  vmap* copy(int share);
  vma* lookup(uptr start, uptr len);
-  int insert(vmnode *n, uptr va_start, int dotlb);
+  long insert(vmnode *n, uptr va_start, int dotlb);
  int remove(uptr start, uptr len);

  int pagefault(uptr va, u32 err);
@@ -104,6 +104,7 @@ private:
  ~vmap();
  NEW_DELETE_OPS(vmap)
  int pagefault_wcow(vma *m);
+  uptr unmapped_area(size_t n);

  struct spinlock brklock_;
 };
--- a/kernel/sysproc.cc
+++ b/kernel/sysproc.cc
@@ -99,12 +99,13 @@ sys_map(uptr addr, u64 len)
  if (vmn == 0)
    return -1;

-  if (myproc()->vmap->insert(vmn, PGROUNDDOWN(addr), 1) < 0) {
+  long r = myproc()->vmap->insert(vmn, PGROUNDDOWN(addr), 1);
+  if (r < 0) {
    delete vmn;
    return -1;
  }

-  return 0;
+  return r;
 }

 long

--- a/kernel/vm.cc
+++ b/kernel/vm.cc
@@ -362,13 +362,23 @@ vmap::lookup(uptr start, uptr len)
  return 0;
 }

-int
+long
 vmap::insert(vmnode *n, uptr vma_start, int dotlb)
 {
  ANON_REGION("vmap::insert", &perfgroup);

  vma *e;
  bool replaced = false;
+  bool fixed = (vma_start != 0);
+
+again:
+  if (!fixed) {
+    vma_start = unmapped_area(n->npages);
+    if (vma_start == 0) {
+      cprintf("vmap::insert: no unmapped areas\n");
+      return -1;
+    }
+  }

  {
    // new scope to release the search lock before tlbflush
@@ -384,6 +394,9 @@ vmap::insert(vmnode *n, uptr vma_start, int dotlb)
      if (!r)
        continue;
 #endif
+      if (!fixed)
+        goto again;
+
      vma *rvma = (vma*) r;
      cprintf("vmap::insert: overlap with %p: 0x%lx--0x%lx\n",
              rvma, rvma->vma_start, rvma->vma_end);
@@ -426,7 +439,8 @@ vmap::insert(vmnode *n, uptr vma_start, int dotlb)
  else
    if (tlb_lazy)
      tlbflush(myproc()->unmap_tlbreq_);
-  return 0;
+
+  return vma_start;
 }

 int
@@ -709,3 +723,19 @@ vmap::sbrk(ssize_t n, uptr *addr)
  brk_ += n;
  return 0;
 }
+
+uptr
+vmap::unmapped_area(size_t npages)
+{
+  size_t n = npages*PGSIZE;
+  uptr addr = 0x1000;
+
+  while (addr < USERTOP) {
+    auto x = cr.search(addr, n);
+    if (x == nullptr)
+      return addr;
+    vma* a = (vma*) x;
+    addr = a->vma_end;
+  }
+  return 0;
+}