Direct Interception

This article dives into the configuration and use of Direct Interception Mode in Object Mount for Linux.

Overview

When running in Direct Interception Mode, Object Mount will insert itself between your applications and the operating system. It will dynamically redirect relevant file system calls made by shell commands and applications to the appropriate APIs of your object storage provider. This dynamic “mapping” between file system concepts and object storage interfaces gives your tools instant access to objects as files.

This direct interception means any applications that can access file storage can now work with object storage. Object Mount intercepts I/O calls from any user binaries, including those written in C/C++, Rust, Go, Java, Python, etc.

It’s built to work everywhere: It works with dynamic binaries and static binaries. It works inside unprivileged containerized environments.

Direct interception Mode uses the LD_PRELOAD environment variable so that Object Mount can capture and redirect storage access library and system calls to object storage APIs.

• If a static binary is intercepted, a JIT ELF binary translator will redirect relevant calls when the binary is loaded into memory.

Highlights

• Direct Interception offers the highest performance access to object storage that Object Mount provides.
• Direct Interception Mode is the default mode and the most common mode for Object Mount to be deployed in.
• Unless otherwise noted, all documentation pages and installation instructions are written assuming you are using “Direct Interception Mode”.

Example Use Cases

• Direct Interception Mode is best suited for situations in which installed app compatibility is not an issue.
• For example: When setting up a fixed workflow with Object Mount that can be tested and verified before putting it into production.

Advantages and Disadvantages

How to Enable

Direct Interception Mode can be enabled per-session or per-command.

Direct Interception: Per-Session

Enable Object Mount for a single shell session by calling cuno from a terminal command line:

$
cuno

$
cuno

This will launch a new interactive “wrapped shell” with Object Mount acting in Direct Interception Mode.

The wrapped shell itself has Object Mount monitoring all its I/O calls — so every command entered or application launched from within the wrapped shell will be monitored and intercepted by Object Mount

Direct Interception: Per-Command

To enable direct interception for a single command, use:

cuno run bash -c "<your command and arguments>"

cuno run bash -c "<your command and arguments>"

Path Usage

Inside a cuno-wrapped shell session, object storage buckets can be accessed using either path or URI formats.

The commands below provide examples of both path and URI usage within a cuno-launched shell:

$
cuno
(cuno)$ ls s3://<bucket>/<path>
(cuno)$ ls /cuno/s3/<bucket>/<path>

$
cuno
(cuno)$ ls s3://<bucket>/<path>
(cuno)$ ls /cuno/s3/<bucket>/<path>

Shell Interaction

bash and zsh are fully supported when using the Object Mount CLI.

This includes support for:

• Tab auto-completion of remote paths
• Wildcard expansion (*) of filesystem and remote paths

In either of these fully-supported shells, the prompt will be prefixed with (cuno) to indicate that Direct Interception is enabled and that you are using an Object Mount CLI-wrapped shell::

(cuno) user@host:~$

(cuno) user@host:~$

Detecting Shells

To select between the two shells, Object Mount determines if either is present using the following methods (in order):

1. The shell used to launch Object Mount
2. The user’s preferred login shell
3. All installed shells

If neither bash nor zsh are found, then the first shell in this list is used. If no shell is set, then /bin/sh is used.

Specifying Shells

To launch a specific shell with Object Mount enabled, use cuno run:

cuno run <shell>

cuno run <shell>