Faasm Host Interface

Faasm Host Interface

To execute functions compiled to WebAssembly, Faasm must define an interfacethat allows these functions to interact with the underlying host and runtime.This interface must support a subset of standard POSIX-like syscalls, as wellas serverless-specific tasks such as state management, and invoking otherfunctions.

Function invocation and chaining

These cover interactions with serverless functions and their ability to invokeother functions ("chaining").

Function	Description
`byte read_call_input()`	Read input data as byte array
`void write_call_output(out_data)`	Write output data for function
`int chain_call(name, args)`	Call function and return `call_id`
`int await_call(call_id)`	Await completion of `call_id`
`byte get_call_output(call_id)`	Load the output data of `call_id`

State

This section of the host interface covers management of state as outlined inthe state docs.

Function	Description
`byte get_state(key, flags)`	Read input data as byte array
`byte get_state_offset(key, off, flags)`	Write output data for function
`void set_state(key, val)`	Write output data for function
`void set_state_offset(key, val, len, off)`	Write output data for function
`void push/pull_state(key)`	Write output data for function
`void push/pull_state_offset(key, off)`	Write output data for function
`void append_state(key, val)`	Write output data for function
`void lock_state_read/write(key)`	Write output data for function
`void lock_state_global_read/write(key)`	Write output data for function

POSIX-like system calls

This section covers "standard" POSIX-like system calls, some of which are also foundin WASI.

Category	Function	Description
Dynamic linking	`void dlopen/dlsym(…)`	Dynamic linking of libraries
Dynamic linking	`int dlclose(…)`	As above
Memory	`void mmap(…), int munmap(…)`	Memory grow/shrink only
Memory	`int brk(…), void* sbrk(…)`	Memory grow/shrink only
Network	`int socket/connect/bind(…)`	Client-side networking only
Network	`size_t send/recv(…)`	Send/recv via virtual interface
File I/O	`int open/close/dup/stat(…)`	Per-user virtual filesystem access
File I/O	`size_t read/write(…)`	As above
Timing	`int gettime(…)`	Per-user monotonic clock only
Random	`size_t getrandom(…)`	Uses underlying `host/dev/urandom`

Further extensions

The Faasm host interface also includes extentions and libraries appropriateto large-scale parallel applications: