capsules_extra

Module isolated_nonvolatile_storage_driver

Source
Expand description

This provides userspace access to nonvolatile storage.

This driver provides isolation between individual userland applications. Each application only has access to its region of nonvolatile memory and cannot read/write to nonvolatile memory of other applications.

Each app is assigned a fixed amount of nonvolatile memory. This amount is set at compile time.

§Storage Layout

Example nonvolatile storage layout (note that | indicates bitwise concatenation):

    ╒════════ ← Start of nonvolatile region
    ├──────── ← Start of App 1's region header
    │ Region version number (8 bits) | Region length (24 bits)
    │ App 1's ShortID (u32)
    │ XOR of previous two u32 fields (u32)
    ├──────── ← Start of App 1's Region          ═╗
    │                                             ║
    │
    │                                            region 1
    │                                            length
    │
    │                                             ║
    │                                            ═╝
    ├──────── ← Start of App 2's region header
    │ Region version number (8 bits) | Region length (24 bits)
    │ App 2's ShortID (u32)
    │ XOR of previous two u32 fields (u32)
    ├──────── ← Start of App 2's Region          ═╗
    │                                             ║
    │
    │
    │                                            region 2
    │                                            length
    │
    │
    │                                             ║
    ...                                          ═╝
    ╘════════ ← End of userspace region

§Storage Initialization

This capsule caches the location of an application’s storage region in grant. This cached location is set on the first usage of this capsule.

Here is a general high-level overview of what happens when an app makes its first syscall:

  1. App engages with the capsule by making any syscall.
  2. Capsule searches through storage to see if that app has an existing region.
  3. a. If the capsule finds a matching region:
    • Cache the app’s region information in its grant. b. If the capsule DOESN’T find a matching region:
    • Allocate a new region for that app.
    • Erase the region’s usable area.
  4. Handle the syscall that the app originally made.
  5. When the syscall finishes, notify the app via upcall.

§Example Software Stack

Here is a diagram of the expected stack with this capsule: Boxes are components and between the boxes are the traits that are the interfaces between components. This capsule only provides a userspace interface.

+------------------------------------------------------------------------+
|                                                                        |
|                             userspace                                  |
|                                                                        |
+------------------------------------------------------------------------+
                            kernel::Driver
+------------------------------------------------------------------------+
|                                                                        |
| isolated_nonvolatile_storage_driver::IsolatedNonvolatileStorage (this) |
|                                                                        |
+------------------------------------------------------------------------+
           hil::nonvolatile_storage::NonvolatileStorage
+------------------------------------------------------------------------+
|                                                                        |
|               Physical nonvolatile storage driver                      |
|                                                                        |
+------------------------------------------------------------------------+

Structs§

App
State stored in the grant region on behalf of each app.
AppRegion
Describes a region of nonvolatile memory that is assigned to a certain app.
IsolatedNonvolatileStorage

Enums§

ManagerTask
Operation referencing a particular region.
NvmCommand
The operation the process requested.
User
What is currently using the underlying nonvolatile storage driver.

Constants§

BUF_LEN
Recommended size for the buffer provided to this capsule.
DRIVER_NUM

Functions§

usize32s_to_usize
Helper function to convert create a full, single usize value from two 32-bit values stored in usizes.