# sd_bus_negotiate_fds

## NAME



           sd_bus_negotiate_fds, sd_bus_negotiate_timestamp,
           sd_bus_negotiate_creds, sd_bus_get_creds_mask - Control feature
           negotiation on bus connections
    


## SYNOPSIS



           **#include <systemd/sd-bus.h>**
    
           **int sd_bus_negotiate_fds(sd_bus ***_bus_**, int** _b_**);**
    
           **int sd_bus_negotiate_timestamp(sd_bus ***_bus_**, int** _b_**);**
    
           **int sd_bus_negotiate_creds(sd_bus ***_bus_**, int** _b_**, uint64_t** _mask_**);**
    
           **int sd_bus_get_creds_mask(sd_bus ***_bus_**, uint64_t ***_mask_**);**
    


## DESCRIPTION



           **sd_bus_negotiate_fds()** controls whether file descriptor passing
           shall be negotiated for the specified bus connection. It takes a
           bus object and a boolean, which, when true, enables file
           descriptor passing, and, when false, disables it. Note that not
           all transports and servers support file descriptor passing. In
           particular, networked transports generally do not support file
           descriptor passing. To find out whether file descriptor passing is
           available after negotiation, use sd_bus_can_send(3) and pass
           **SD_BUS_TYPE_UNIX_FD**. Note that file descriptor passing is always
           enabled for both sending and receiving or for neither, but never
           only in one direction. By default, file descriptor passing is
           negotiated for all connections.
    
           **sd_bus_negotiate_timestamp()** controls whether implicit sender
           timestamps shall be attached automatically to all incoming
           messages. Takes a bus object and a boolean, which, when true,
           enables timestamping, and, when false, disables it. Use
           sd_bus_message_get_monotonic_usec(3),
           sd_bus_message_get_realtime_usec(3), sd_bus_message_get_seqnum(3)
           to query the timestamps of incoming messages. If negotiation is
           disabled or not supported, these calls will fail with **-ENODATA**.
           Note that currently no transports support timestamping of
           messages. By default, message timestamping is not negotiated for
           connections.
    
           **sd_bus_negotiate_creds()** controls whether and which implicit
           sender credentials shall be attached automatically to all incoming
           messages. Takes a bus object and a boolean indicating whether to
           enable or disable the credential parts encoded in the bit mask
           value argument. Note that not all transports support attaching
           sender credentials to messages, or do not support all types of
           sender credential parameters, or might suppress them under certain
           circumstances for individual messages. Specifically, dbus1 only
           supports **SD_BUS_CREDS_UNIQUE_NAME**. The sender credentials are
           suitable for authorization decisions. By default, only
           **SD_BUS_CREDS_WELL_KNOWN_NAMES** and **SD_BUS_CREDS_UNIQUE_NAME** are
           enabled. In fact, these two credential fields are always sent
           along and cannot be turned off.
    
           **sd_bus_get_creds_mask()** returns the set of sender credentials that
           was negotiated to be attached to all incoming messages in _mask_.
           This value is an upper boundary only. Hence, always make sure to
           explicitly check which credentials are attached to a specific
           message before using it.
    
           The **sd_bus_negotiate_fds()** function may be called only before the
           connection has been started with sd_bus_start(3). Both
           **sd_bus_negotiate_timestamp()** and **sd_bus_negotiate_creds()** may also
           be called after a connection has been set up. Note that, when
           operating on a connection that is shared between multiple
           components of the same program (for example via
           sd_bus_default(3)), it is highly recommended to only enable
           additional per message metadata fields, but never disable them
           again, in order not to disable functionality needed by other
           components.
    


## RETURN VALUE



           On success, these functions return a non-negative integer. On
           failure, they return a negative errno-style error code.
    
       **Errors**
           Returned errors may indicate the following problems:
    
           **-EPERM**
               The bus connection has already been started.
    
           **-EINVAL**
               An argument is invalid.
    
               Added in version 246.
    
           **-ENOPKG**
               The bus cannot be resolved.
    
               Added in version 246.
    
           **-ECHILD**
               The bus was created in a different process, library or module
               instance.
    
               Added in version 246.
    


## NOTES



           Functions described here are available as a shared library, which
           can be compiled against and linked to with the
           **libsystemd pkg-config**(1) file.
    
           The code described here uses getenv(3), which is declared to be
           not multi-thread-safe. This means that the code calling the
           functions described here must not call setenv(3) from a parallel
           thread. It is recommended to only do calls to **setenv()** from an
           early phase of the program when no other threads have been
           started.
    


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