[Feature]: Support Multiple Block Devices in Rumprun / Solo5

[Rucha0901]

Problem Description

Solo5 hypervisors (solo5-hvt, solo5-spt) expect block device IDs to match the names specified in the unikernel's manifest. Currently, urunc simplifies this by only supporting a single block device, hardcoded as rootfs. Users cannot attach secondary volume disks to Rumprun unikernel instances, which limits database or log storage use cases.

Proposed Solution

1. Update Rumprun struct to track all block devices provided in UnikernelParams.Block.
2. Update MonitorBlockCli in rumprun.go to iterate over all devices in UnikernelParams.Block rather than returning only the hardcoded rootfs entry.
3. Support custom block device IDs when specified in BlockDevParams, falling back to rootfs for index 0 and vol<index> for secondary volumes.

[cmainas]

Hello @Rucha0901 ,

indeed this is something we can support. Do you have any specific use case which we can use as a reference for rumprun?

[Rucha0901]

Hi @cmainas,

A typical use case is running a stateful application (like a database or web server) on Rumprun where the main application binary/system runs on the rootfs block device, while persistent data or logs are mounted on a secondary block device (e.g., /mnt/data or /db).

Would you like us to include a sample multi-volume setup or integration test as a reference for this PR?