# `demi_init()`

## Name

`demi_init` - Initializes Demikernel.

## Synopsis

```c
#include <demi/libos.h>

int demi_init(int argc, char *const argv[]);
```

## Description

`demi_init()` initializes Demikernel. It sets up devices, instantiates LibOSes, and performs general initialization
tasks.

The `argv` parameter is an array of argument strings passed to Demikernel. The `argc` parameter is a positive integer
that specifies the length of that array.

The array of argument strings provides Demikernel with various information that are critical for its initialization. For
instance, these arguments shall state which LibOSes should be initialized, and whether or not runtime features shall be
turned on.

All arguments supported by Demikernel are listed in the table below. Arguments that are not listed therein are ignored.

| ID      | Argument      | Description                       | Supported OS |
| ------- | ------------- | --------------------------------- | ------------ |
| `ARG-2` | `--catloop`   | Enables TCP Socket Loopback LibOS | Linux        |
| `ARG-3` | `--catmem`    | Enables Shared Memory LibOS       | Linux        |
| `ARG-4` | `--catnap`    | Enables Linux Sockets LibOS       | Linux        |
| `ARG-5` | `--catnip`    | Enables DPDK LibOS                | Linux        |
| `ARG-6` | `--catpowder` | Enables Linux Raw Sockets LibOS   | Linux        |

These arguments are mutually exclusive. Demikernel currently does not support multiple LibOSes to co-exist.
[Issue #158](https://github.com/demikernel/demikernel/issues/158) tracks progress of this feature.

## Return Value

On success, zero is returned. On error, a positive error code is returned and any subsequent call to Demikernel may
result in unexpected behavior.

## Errors

On error, one of the following positive error codes is returned:

- `EINVAL` - The `argc` argument is less than or equal to zero.
- `EINVAL` - The `argv` argument is `NULL`.
- `EEXIST` - The LibOS has already been initialized.

## Conforming To

Error codes are conformant to [POSIX.1-2017](https://pubs.opengroup.org/onlinepubs/9699919799/nframe.html).

## Bugs

Demikernel may fail with error codes that are not listed in this manual page.

## Disclaimer

Any behavior that is not documented in this manual page is unintentional and should be reported.