Index: lib/libc/sys/minherit.2 =================================================================== --- lib/libc/sys/minherit.2 +++ lib/libc/sys/minherit.2 @@ -29,7 +29,7 @@ .\" .\" @(#)minherit.2 8.1 (Berkeley) 6/9/93 .\" -.Dd October 30, 2007 +.Dd March 15, 2017 .Dt MINHERIT 2 .Os .Sh NAME @@ -91,6 +91,11 @@ after the parent forks and there is no way to get the previous shared-backing-store mapping without unmapping and remapping the address space in the parent. +.It Dv INHERIT_ZERO +This option causes the address space in question to be mapped as new +anonymous pages, +which would be initialized to all zero bytes, +in the child process. .El .Sh RETURN VALUES .Rv -std minherit @@ -130,6 +135,13 @@ .Ox and then in .Fx 2.2 . +.Pp +The +.Dv INHERIT_ZERO +support first appeared in +.Ox 5.6 +and then in +.Fx 12.0 . .Sh BUGS Once you set inheritance to .Dv MAP_PRIVATE Index: sys/sys/mman.h =================================================================== --- sys/sys/mman.h +++ sys/sys/mman.h @@ -43,6 +43,7 @@ #define INHERIT_SHARE 0 #define INHERIT_COPY 1 #define INHERIT_NONE 2 +#define INHERIT_ZERO 3 #endif /* Index: sys/vm/vm.h =================================================================== --- sys/vm/vm.h +++ sys/vm/vm.h @@ -68,6 +68,7 @@ #define VM_INHERIT_SHARE ((vm_inherit_t) 0) #define VM_INHERIT_COPY ((vm_inherit_t) 1) #define VM_INHERIT_NONE ((vm_inherit_t) 2) +#define VM_INHERIT_ZERO ((vm_inherit_t) 3) #define VM_INHERIT_DEFAULT VM_INHERIT_COPY typedef u_char vm_prot_t; /* protection codes */ Index: sys/vm/vm_map.c =================================================================== --- sys/vm/vm_map.c +++ sys/vm/vm_map.c @@ -2285,6 +2285,7 @@ case VM_INHERIT_NONE: case VM_INHERIT_COPY: case VM_INHERIT_SHARE: + case VM_INHERIT_ZERO: break; default: return (KERN_INVALID_ARGUMENT); @@ -3442,6 +3443,36 @@ vmspace_map_entry_forked(vm1, vm2, new_entry); vm_map_copy_entry(old_map, new_map, old_entry, new_entry, fork_charge); + break; + + case VM_INHERIT_ZERO: + /* + * Create a new anonymous mapping entry modelled from + * the old one. + */ + new_entry = vm_map_entry_create(new_map); + memset(new_entry, 0, sizeof(*new_entry)); + + new_entry->start = old_entry->start; + new_entry->end = old_entry->end; + new_entry->avail_ssize = old_entry->avail_ssize; + new_entry->adj_free = old_entry->adj_free; + new_entry->max_free = old_entry->max_free; + new_entry->eflags = old_entry->eflags & + ~(MAP_ENTRY_USER_WIRED | MAP_ENTRY_IN_TRANSITION | + MAP_ENTRY_VN_WRITECNT); + new_entry->protection = old_entry->protection; + new_entry->max_protection = old_entry->max_protection; + new_entry->inheritance = VM_INHERIT_ZERO; + + vm_map_entry_link(new_map, new_map->header.prev, + new_entry); + vmspace_map_entry_forked(vm1, vm2, new_entry); + + new_entry->cred = curthread->td_ucred; + crhold(new_entry->cred); + *fork_charge += (new_entry->end - new_entry->start); + break; } old_entry = old_entry->next;