---
layout: manual
Content-Style: 'text/css'
title: _MP(RPMEM_PERSIST, 3)
collection: librpmem
header: PMDK
date: rpmem API version 1.2
...

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[comment]: <> (rpmem_persist.3 -- man page for rpmem persist and read functions)

[NAME](#name)<br />
[SYNOPSIS](#synopsis)<br />
[DESCRIPTION](#description)<br />
[RETURN VALUE](#return-value)<br />
[SEE ALSO](#see-also)<br />


# NAME #

**rpmem_persist**(), **rpmem_deep_persist**(), **rpmem_read**(),
- functions to copy and read remote pools


# SYNOPSIS #

```c
#include <librpmem.h>

int rpmem_persist(RPMEMpool *rpp, size_t offset,
	size_t length, unsigned lane, unsigned flags);
int rpmem_deep_persist(RPMEMpool *rpp, size_t offset,
	size_t length, unsigned lane);
int rpmem_read(RPMEMpool *rpp, void *buff, size_t offset,
	size_t length, unsigned lane);
```


# DESCRIPTION #

The **rpmem_persist**() function copies data of given *length* at given
*offset* from the associated local memory pool and makes sure the data is
persistent on the remote node before the function returns. The remote node
is identified by the *rpp* handle which must be returned from either
**rpmem_open**(3) or **rpmem_create**(3). The *offset* is relative
to the *pool_addr* specified in the **rpmem_open**(3) or **rpmem_create**(3)
call. If the remote pool was created using **rpmem_create**() with non-NULL
*create_attr* argument, *offset* has to be greater or equal to 4096.
In that case the first 4096 bytes of the pool is used for storing the pool
matadata and cannot be overwritten.
If the pool was created with NULL *create_attr* argument, the pool metadata
is not stored with the pool and *offset* can be any nonnegative number.
The *offset* and *length* combined must not exceed the
*pool_size* passed to **rpmem_open**(3) or **rpmem_create**(3).
The **rpmem_persist**() operation is performed using the given *lane* number.
The lane must be less than the value returned by **rpmem_open**(3) or
**rpmem_create**(3) through the *nlanes* argument (so it can take a value
from 0 to *nlanes* - 1). The *flags* argument can be 0 or RPMEM_PERSIST_RELAXED
which means the persist operation will be done without any guarantees regarding
atomicity of memory transfer.

The **rpmem_deep_persist**() function works in the same way as
**rpmem_persist**(3) function, but additionally it flushes the data to the
lowest possible persistency domain available from software.
Please see **pmem_deep_persist**(3) for details.

The **rpmem_read**() function reads *length* bytes of data from a remote pool
at *offset* and copies it to the buffer *buff*. The operation is performed on
the specified *lane*. The lane must be less than the value returned by
**rpmem_open**(3) or **rpmem_create**(3) through the *nlanes* argument
(so it can take a value from 0 to *nlanes* - 1). The *rpp* must point to a
remote pool opened or created previously by **rpmem_open**(3) or
**rpmem_create**(3).


# RETURN VALUE #

The **rpmem_persist**() function returns 0 if the entire memory area was
made persistent on the remote node. Otherwise it returns a non-zero value
and sets *errno* appropriately.

The **rpmem_read**() function returns 0 if the data was read entirely.
Otherwise it returns a non-zero value and sets *errno* appropriately.


# SEE ALSO #

**rpmem_create**(3), **rpmem_open**(3), **rpmem_persist**(3),
**sysconf**(3), **limits.conf**(5), **libpmemobj**(7)
and **<http://pmem.io>**
