nbd\_set\_private\_data(3) LIBNBD nbd\_set\_private\_data(3)

# [NAME](#NAME)

nbd\_set\_private\_data - set the per-handle private data

# [SYNOPSIS](#SYNOPSIS)

```
 #include <libnbd.h>
 uintptr_t nbd_set_private_data (
             struct nbd_handle *h, uintptr_t private_data
           );
```

# [DESCRIPTION](#DESCRIPTION)

Handles contain a private data field for applications to use for any purpose. This function sets the value of this field and returns the old value (or 0 if it was not previously set).

When calling libnbd from C, the type of this field is "uintptr\_t" so it can be used to store an unsigned integer or a pointer.

In non-C bindings it can be used to store an unsigned integer.

Libnbd does not use or interpret the value at all (except to return it when you call [**nbd\_get\_private\_data**(3)](/man/os/libnbd/nbd_get_private_data.3)). In particular, if the value is a pointer then it is not freed when the handle is closed. If you want that behaviour, see [**nbd\_add\_close\_callback**(3)](/man/os/libnbd/nbd_add_close_callback.3).

# [RETURN VALUE](#RETURN_VALUE)

This call returns a "uintptr\_t".

# [ERRORS](#ERRORS)

This function does not fail.

The following parameters must not be NULL: "h". For more information see "Non-NULL parameters" in [**libnbd**(3)](/man/os/libnbd/libnbd.3).

# [VERSION](#VERSION)

This function first appeared in libnbd 1.8.

If you need to test if this function is available at compile time check if the following macro is defined:

```
 #define LIBNBD_HAVE_NBD_SET_PRIVATE_DATA 1
```

# [SEE ALSO](#SEE_ALSO)

[**nbd\_add\_close\_callback**(3)](/man/os/libnbd/nbd_add_close_callback.3), [**nbd\_create**(3)](/man/os/libnbd/nbd_create.3), [**nbd\_get\_private\_data**(3)](/man/os/libnbd/nbd_get_private_data.3), [**libnbd**(3)](/man/os/libnbd/libnbd.3).

# [AUTHORS](#AUTHORS)

Eric Blake

Richard W.M. Jones

# [COPYRIGHT](#COPYRIGHT)

Copyright Red Hat

# [LICENSE](#LICENSE)

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

2026-10-13 libnbd-1.25.8

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Document: nbd_set_private_data(3) from libnbd 1.25.8-r0 (Chainguard OS)