| # Userboot |
| |
| ## Userboot Protocol (`fuchsia.boot.Userboot`) |
| |
| The booted program (`userboot.next`) receives the server end of a |
| `fuchsia.boot.Userboot` channel in its bootstrap message as `PA_USER0` with |
| argument `0`. |
| |
| Userboot sends pipelined one-way messages on this channel before closing its |
| client end: |
| - `fuchsia.boot.Userboot/PostStashSvc`: Transfers the server end of the |
| `fuchsia.boot.SvcStash` protocol to the booted program. |
| - `fuchsia.boot.Userboot/PostBootfsVmo`: Transfers the uncompressed BOOTFS VMO |
| to the booted program. |
| - `fuchsia.boot.Userboot/PostBootfsFiles`: Transfers the executable BOOTFS file |
| VMOs already extracted for the first process and its loader service so that |
| the booted program (e.g., `component_manager`) can reuse them without |
| duplicating pages. |
| - `fuchsia.boot.Userboot/PostBootHandles`: Transfers non-bootstrap handles |
| provided by the kernel (such as the ZBI VMO, kernel file VMOs, and system, |
| MMIO, IRQ, I/O port, and SMC resource handles) to the booted program. |
| |
| ## Svc Stub and Svc Stash (`fuchsia.boot.SvcStash`) |
| |
| Processes launched by userboot may be provided with a handle of `PA_NS_DIR` |
| type and path `/svc`. This allows early boot processes to pipeline requests to |
| services that will eventually become available (such as |
| `fuchsia.debugdata.Publisher`). |
| |
| For each launched process given a `/svc` handle, userboot sends the |
| corresponding server end to the `SvcStash` channel via |
| `fuchsia.boot.SvcStash/Store`. |
| |
