nbd\_set\_debug\_callback(3) LIBNBD nbd\_set\_debug\_callback(3)

# [NAME](#NAME)

nbd\_set\_debug\_callback - set the debug callback

# [SYNOPSIS](#SYNOPSIS)

```
 #include <libnbd.h>
 typedef struct {
   int (*callback) (void *user_data, const char *context,
                    const char *msg);
   void *user_data;
   void (*free) (void *user_data);
 } nbd_debug_callback;
 int nbd_set_debug_callback (
       struct nbd_handle *h,
       nbd_debug_callback debug_callback
     );
```

# [DESCRIPTION](#DESCRIPTION)

Set the debug callback. This function is called when the library emits debug messages, when debugging is enabled on a handle. The callback parameters are "user\_data" passed to this function, the name of the libnbd function emitting the debug message ("context"), and the message itself ("msg"). If no debug callback is set on a handle then messages are printed on "stderr".

The callback should not call "nbd\_\*" APIs on the same handle since it can be called while holding the handle lock and will cause a deadlock.

# [RETURN VALUE](#RETURN_VALUE)

If the call is successful the function returns 0.

# [ERRORS](#ERRORS)

On error -1 is returned.

Refer to "ERROR HANDLING" in [**libnbd**(3)](/man/os/libnbd/libnbd.3) for how to get further details of the error.

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 1.0.

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_DEBUG_CALLBACK 1
```

# [SEE ALSO](#SEE_ALSO)

[**nbd\_create**(3)](/man/os/libnbd/nbd_create.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_debug_callback(3) from libnbd 1.25.8-r0 (Chainguard OS)