---
name: "sd_bus_message_append_string_memfd"
section: "3"
platform: "linux"
package: "systemd-libs"
version: "262.1-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/sd_bus_message_append_string_memfd"
---

# sd\_bus\_message\_append\_string\_memfd(3)

Attach a string to a message

## NAME

sd\_bus\_message\_append\_string\_memfd, sd\_bus\_message\_append\_string\_iovec, sd\_bus\_message\_append\_string\_space - Attach a string to a message

## SYNOPSIS

```
#include <systemd/sd-bus.h>
```

**int sd\_bus\_message\_append\_string\_memfd(sd\_bus\_message \****m***, int** *memfd***, uint64\_t** *offset***, uint64\_t** *size***);**

**int sd\_bus\_message\_append\_string\_iovec(sd\_bus\_message \****m***, const struct iovec \****iov***, unsigned** *n***);**

**int sd\_bus\_message\_append\_string\_space(sd\_bus\_message \****m***, size\_t** *size***, char \*\****ret***);**

## DESCRIPTION

The functions **sd\_bus\_message\_append\_string\_memfd()** and **sd\_bus\_message\_append\_string\_iovec()** can be used to append a single string (item of type "s") to message *m*.

In case of **sd\_bus\_message\_append\_string\_memfd()**, the contents of *memfd* starting at the specified *offset* and of the specified *size* are used as the string. *size* must include the terminating **NUL** byte, i.e. the resulting string has length *size* - 1. If *offset* is zero and *size* is **UINT64\_MAX**, the full contents of the memory file descriptor are used, and hence must themselves end in a **NUL** byte. If *offset* plus *size* exceeds the actual size of the memory file descriptor, this call fails with **-EMSGSIZE**. The memory file descriptor is sealed by this call if it has not been sealed yet, and cannot be modified after this call. The appended contents must satisfy the same constraints as described for the "s" type in [**sd\_bus\_message\_append\_basic**(3)](/sd_bus_message_append_basic/3.md).

In case of **sd\_bus\_message\_append\_string\_iovec()**, the payload of *iov* is the string. It must satisfy the same constraints as described for the "s" type in [**sd\_bus\_message\_append\_basic**(3)](/sd_bus_message_append_basic/3.md).

The *iov* argument must point to *n* struct iovec structures. Each structure may have the iov\_base field set, in which case the memory pointed to will be copied into the message, or unset, in which case a block of spaces (ASCII 32) of length iov\_len will be inserted. The memory pointed at by *iov* may be changed after this call.

The **sd\_bus\_message\_append\_string\_space()** function appends space for a string to message *m*. It behaves similar to **sd\_bus\_message\_append\_basic()** with type "s", but instead of copying a string into the message, it returns a pointer to the destination area to the caller in pointer *ret*. Space for the string of length *size* plus the terminating **NUL** is allocated.

## RETURN VALUE

On success, those calls return 0 or a positive integer. On failure, they return a negative errno-style error code.

### Errors

Returned errors may indicate the following problems:

**-EINVAL**

Specified parameter is invalid.

**-EPERM**

Message has been sealed.

**-ESTALE**

Message is in invalid state.

**-ENXIO**

Message cannot be appended to.

**-ENOMEM**

Memory allocation failed.

## NOTES

Functions described here are available as a shared library, which can be compiled against and linked to with the **libsystemd** [**pkg-config**(1)](/pkg-config/1.md) file.

All functions listed here are thread-agnostic and only a single thread may operate on a given object at any given time. Different threads may access the same object at different times. Multiple independent objects may be used from different threads in parallel.

The code described here uses [**getenv**(3)](/getenv/3.md), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call [**setenv**(3)](/setenv/3.md) 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.

## SEE ALSO

[**systemd**(1)](/systemd/1.md), [**sd-bus**(3)](/sd-bus/3.md), [**sd\_bus\_message\_append\_basic**(3)](/sd_bus_message_append_basic/3.md), **The D-Bus specification**\[1\]

## NOTES

- 1\.

  The D-Bus specification

  https://dbus.freedesktop.org/doc/dbus-specification.html