---
name: "knet_handle_enable_pmtud_notify"
section: "3"
platform: "linux"
package: "libknet-doc"
version: "1.31-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/knet_handle_enable_pmtud_notify"
---

# knet\_handle\_enable\_pmtud\_notify(3)

install a callback to receive PMTUd changes

## NAME

knet\_handle\_enable\_pmtud\_notify - install a callback to receive PMTUd changes

## SYNOPSIS

```
#include <libknet.h>

int knet_handle_enable_pmtud_notify(
    knet_handle_t                                       knet_h,
    void                                               *pmtud_notify_fn_private_data,
    void(*)(void *private_data, unsigned int data_mtu)  pmtud_notify_fn
);
```

## DESCRIPTION

knet\_handle\_enable\_pmtud\_notify

knet\_h - pointer to knet\_handle\_t

pmtud\_notify\_fn\_private\_data void pointer to data that can be used to identify the callback.

pmtud\_notify\_fn is a callback function that is invoked every time a path MTU size change is detected. The function allows libknet to notify the user of data MTU, that's the max value that can be send onwire without fragmentation. The data MTU will always be lower than real link MTU because it accounts for protocol overhead, knet packet header and (if configured) crypto overhead, This function MUST NEVER block or add substantial delays.

## RETURN VALUE

knet\_handle\_enable\_pmtud\_notify returns 0 on success -1 on error and errno is set.

## SEE ALSO

[*knet\_handle\_remove\_datafd*(3)](/knet_handle_remove_datafd/3.md), [*knet\_handle\_get\_stats*(3)](/knet_handle_get_stats/3.md), [*knet\_host\_add*(3)](/knet_host_add/3.md), [*knet\_handle\_pmtud\_setfreq*(3)](/knet_handle_pmtud_setfreq/3.md), [*knet\_handle\_pmtud\_get*(3)](/knet_handle_pmtud_get/3.md), [*knet\_handle\_crypto\_use\_config*(3)](/knet_handle_crypto_use_config/3.md), [*knet\_host\_get\_id\_by\_host\_name*(3)](/knet_host_get_id_by_host_name/3.md), [*knet\_host\_get\_status*(3)](/knet_host_get_status/3.md), [*knet\_link\_add\_acl*(3)](/knet_link_add_acl/3.md), [*knet\_link\_get\_pong\_count*(3)](/knet_link_get_pong_count/3.md), [*knet\_link\_get\_priority*(3)](/knet_link_get_priority/3.md), [*knet\_handle\_free*(3)](/knet_handle_free/3.md), [*knet\_handle\_enable\_sock\_notify*(3)](/knet_handle_enable_sock_notify/3.md), [*knet\_handle\_get\_datafd*(3)](/knet_handle_get_datafd/3.md), [*knet\_recv*(3)](/knet_recv/3.md), [*knet\_link\_get\_ping\_timers*(3)](/knet_link_get_ping_timers/3.md), [*knet\_log\_get\_subsystem\_id*(3)](/knet_log_get_subsystem_id/3.md), [*knet\_host\_remove*(3)](/knet_host_remove/3.md), [*knet\_host\_enable\_status\_change\_notify*(3)](/knet_host_enable_status_change_notify/3.md), [*knet\_strtoaddr*(3)](/knet_strtoaddr/3.md), [*knet\_link\_rm\_acl*(3)](/knet_link_rm_acl/3.md), [*knet\_send*(3)](/knet_send/3.md), [*knet\_handle\_get\_transport\_reconnect\_interval*(3)](/knet_handle_get_transport_reconnect_interval/3.md), [*knet\_link\_get\_enable*(3)](/knet_link_get_enable/3.md), [*knet\_link\_set\_priority*(3)](/knet_link_set_priority/3.md), [*knet\_log\_set\_loglevel*(3)](/knet_log_set_loglevel/3.md), [*knet\_handle\_get\_channel*(3)](/knet_handle_get_channel/3.md), [*knet\_link\_get\_config*(3)](/knet_link_get_config/3.md), [*knet\_link\_get\_link\_list*(3)](/knet_link_get_link_list/3.md), [*knet\_get\_transport\_list*(3)](/knet_get_transport_list/3.md), [*knet\_get\_transport\_id\_by\_name*(3)](/knet_get_transport_id_by_name/3.md), [*knet\_log\_get\_loglevel\_id*(3)](/knet_log_get_loglevel_id/3.md), [*knet\_handle\_new\_ex*(3)](/knet_handle_new_ex/3.md), [*knet\_host\_set\_name*(3)](/knet_host_set_name/3.md), [*knet\_addrtostr*(3)](/knet_addrtostr/3.md), [*knet\_handle\_setfwd*(3)](/knet_handle_setfwd/3.md), [*knet\_get\_compress\_list*(3)](/knet_get_compress_list/3.md), [*knet\_host\_set\_policy*(3)](/knet_host_set_policy/3.md), [*knet\_get\_transport\_name\_by\_id*(3)](/knet_get_transport_name_by_id/3.md), [*knet\_handle\_enable\_filter*(3)](/knet_handle_enable_filter/3.md), [*knet\_handle\_crypto\_rx\_clear\_traffic*(3)](/knet_handle_crypto_rx_clear_traffic/3.md), [*knet\_handle\_compress*(3)](/knet_handle_compress/3.md), [*knet\_link\_get\_status*(3)](/knet_link_get_status/3.md), [*knet\_handle\_add\_datafd*(3)](/knet_handle_add_datafd/3.md), [*knet\_send\_sync*(3)](/knet_send_sync/3.md), [*knet\_log\_get\_loglevel\_name*(3)](/knet_log_get_loglevel_name/3.md), [*knet\_handle\_enable\_access\_lists*(3)](/knet_handle_enable_access_lists/3.md), [*knet\_host\_get\_host\_list*(3)](/knet_host_get_host_list/3.md), [*knet\_host\_get\_policy*(3)](/knet_host_get_policy/3.md), [*knet\_link\_set\_enable*(3)](/knet_link_set_enable/3.md), [*knet\_link\_set\_pong\_count*(3)](/knet_link_set_pong_count/3.md), [*knet\_log\_get\_subsystem\_name*(3)](/knet_log_get_subsystem_name/3.md), [*knet\_host\_get\_name\_by\_host\_id*(3)](/knet_host_get_name_by_host_id/3.md), [*knet\_link\_clear\_config*(3)](/knet_link_clear_config/3.md), [*knet\_log\_get\_loglevel*(3)](/knet_log_get_loglevel/3.md), [*knet\_handle\_new*(3)](/knet_handle_new/3.md), [*knet\_handle\_pmtud\_getfreq*(3)](/knet_handle_pmtud_getfreq/3.md), [*knet\_handle\_pmtud\_set*(3)](/knet_handle_pmtud_set/3.md), [*knet\_handle\_clear\_stats*(3)](/knet_handle_clear_stats/3.md), [*knet\_link\_set\_config*(3)](/knet_link_set_config/3.md), [*knet\_handle\_crypto\_set\_config*(3)](/knet_handle_crypto_set_config/3.md), [*knet\_handle\_crypto*(3)](/knet_handle_crypto/3.md), [*knet\_get\_crypto\_list*(3)](/knet_get_crypto_list/3.md), [*knet\_handle\_set\_transport\_reconnect\_interval*(3)](/knet_handle_set_transport_reconnect_interval/3.md), [*knet\_link\_clear\_acl*(3)](/knet_link_clear_acl/3.md), [*knet\_link\_set\_ping\_timers*(3)](/knet_link_set_ping_timers/3.md), [*knet\_link\_insert\_acl*(3)](/knet_link_insert_acl/3.md)

## COPYRIGHT

Copyright (C) 2010-2025 Red Hat, Inc. All rights reserved.