libibverbs/man/ibv_fork_init.3.md

---
date: 2006-10-31
footer: libibverbs
header: "Libibverbs Programmer's Manual"
layout: page
license: 'Licensed under the OpenIB.org BSD license (FreeBSD Variant) - See COPYING.md'
section: 3
title: IBV_FORK_INIT
---

# NAME

ibv_fork_init - initialize libibverbs to support fork()

# SYNOPSIS

```c
#include <infiniband/verbs.h>

int ibv_fork_init(void);
```

# DESCRIPTION

**ibv_fork_init()** initializes libibverbs's data structures to handle
**fork()** function calls correctly and avoid data corruption, whether
**fork()** is called explicitly or implicitly (such as in **system()**).

It is not necessary to use this function if all parent process threads are
always blocked until all child processes end or change address spaces via an
**exec()** operation.

# RETURN VALUE

**ibv_fork_init()** returns 0 on success, or the value of errno on failure
(which indicates the failure reason). An error value of EINVAL indicates that
there had been RDMA memory registration already and it is therefore not
safe anymore to fork.

# NOTES

**ibv_fork_init()** works on Linux kernels supporting the **MADV_DONTFORK**
flag for **madvise()** (2.6.17 and higher).

Setting the environment variable **RDMAV_FORK_SAFE** or **IBV_FORK_SAFE** has
the same effect as calling **ibv_fork_init()**.

Setting the environment variable **RDMAV_HUGEPAGES_SAFE** tells the library to
check the underlying page size used by the kernel for memory regions.  This is
required if an application uses huge pages either directly or indirectly via a
library such as libhugetlbfs.

Calling **ibv_fork_init()** will reduce performance due to an extra system
call for every memory registration, and the additional memory allocated to
track memory regions.  The precise performance impact depends on the workload
and usually will not be significant.

Setting **RDMAV_HUGEPAGES_SAFE** adds further overhead to all memory
registrations.

# SEE ALSO

**exec**(3),
**fork**(2),
**ibv_get_device_list**(3),
**system**(3),
**wait**(2)

# AUTHOR

Dotan Barak <dotanba@gmail.com>