Tweak MDB_FIXEDMAP handling.

Drop mmap()'s MAP_FIXED flag, so it returns another address instead
of unmapping existing overlapping pages. Verify the returned address.

diff --git a/libraries/libmdb/mdb.c b/libraries/libmdb/mdb.c
index 6771829152e390188632675ee78e95d941a2713e..32dbf63544c40100b3509edb7d034414b2fe8a39 100644 (file)
--- a/libraries/libmdb/mdb.c
+++ b/libraries/libmdb/mdb.c
@@ -2651,8 +2651,6 @@ mdb_env_open2(MDB_env *env)
        }
 #else
        i = MAP_SHARED;
-       if (meta.mm_address && (flags & MDB_FIXEDMAP))
-               i |= MAP_FIXED;
        prot = PROT_READ;
        if (flags & MDB_WRITEMAP) {
                prot |= PROT_WRITE;
@@ -2674,6 +2672,13 @@ mdb_env_open2(MDB_env *env)
                if (i != MDB_SUCCESS) {
                        return i;
                }
+       } else if (meta.mm_address && env->me_map != meta.mm_address) {
+               /* Can happen because the address argument to mmap() is just a
+                * hint.  mmap() can pick another, e.g. if the range is in use.
+                * The MAP_FIXED flag would prevent that, but then mmap could
+                * instead unmap existing pages to make room for the new map.
+                */
+               return EBUSY;   /* TODO: Make a new MDB_* error code? */
        }
        env->me_psize = meta.mm_psize;