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//! Low level interface for Key-Value (KV) Stores
//!
//! The KV store implementation in Tock has three levels, described below.
//!
//! 1 - Hardware Level:
//! This level is the interface that writes a buffer to the hardware. This will
//! generally be writing to flash, although in theory it would be possible to
//! write to other mediums.
//!
//! An example of the HIL used here is the Tock Flash HIL.
//!
//! 2 - KV System Level:
//! This level can be thought of like a file system. It is responsible for
//! taking save/load operations and generating a buffer to pass to level 1
//! This level is also in charge of generating hashes and checksums.
//!
//! This level allows generating a key hash but otherwise operates on
//! hashed keys. This level is not responsible for permission checks.
//!
//! This file describes the HIL for this level.
//!
//! 3 - KV Store:
//! This is a user friendly high level API. This API is used inside the kernel
//! and exposed to applications to allow KV operations. The API from this level
//! should be high level, for example set/get/delete on unhashed keys.
//! This level is in charge of enforcing permissions.
//!
//! This level is also in charge of generating the key hash by calling into
//! level 2.
//!
//! The expected setup inside Tock will look like this:
//! +-----------------------+
//! | |
//! | Capsule using K-V |
//! | |
//! +-----------------------+
//!
//! capsules::kv_store
//!
//! +-----------------------+
//! | |
//! | K-V in Tock |
//! | |
//! +-----------------------+
//!
//! hil::kv_system (this file)
//!
//! +-----------------------+
//! | |
//! | K-V library |
//! | |
//! +-----------------------+
//!
//! hil::flash
use crate::ErrorCode;
/// The type of keys, this should define the output size of the digest
/// operations.
pub trait KeyType: Eq + Copy + Clone + Sized + AsRef<[u8]> + AsMut<[u8]> {}
impl KeyType for [u8; 8] {}
/// Implement this trait and use `set_client()` in order to receive callbacks.
pub trait StoreClient<K: KeyType> {
/// This callback is called when the get operation completes
///
/// `result`: Nothing on success, 'ErrorCode' on error
/// `key`: The key buffer
/// `ret_buf`: The ret_buf buffer
fn get_complete(
&self,
result: Result<(), ErrorCode>,
key: &'static mut [u8],
ret_buf: &'static mut [u8],
);
/// This callback is called when the set operation completes
///
/// `result`: Nothing on success, 'ErrorCode' on error
/// `key`: The key buffer
/// `value`: The value buffer
fn set_complete(
&self,
result: Result<(), ErrorCode>,
key: &'static mut [u8],
value: &'static mut [u8],
);
/// This callback is called when the delete operation completes
///
/// `result`: Nothing on success, 'ErrorCode' on error
/// `key`: The key buffer
fn delete_complete(&self, result: Result<(), ErrorCode>, key: &'static mut [u8]);
}
/// Implement this trait and use `set_client()` in order to receive callbacks.
pub trait Client<K: KeyType> {
/// This callback is called when the append_key operation completes
///
/// `result`: Nothing on success, 'ErrorCode' on error
/// `unhashed_key`: The unhashed_key buffer
/// `key_buf`: The key_buf buffer
fn generate_key_complete(
&self,
result: Result<(), ErrorCode>,
unhashed_key: &'static mut [u8],
key_buf: &'static mut K,
);
/// This callback is called when the append_key operation completes
///
/// `result`: Nothing on success, 'ErrorCode' on error
/// `key`: The key buffer
/// `value`: The value buffer
fn append_key_complete(
&self,
result: Result<(), ErrorCode>,
key: &'static mut K,
value: &'static mut [u8],
);
/// This callback is called when the get_value operation completes
///
/// `result`: Nothing on success, 'ErrorCode' on error
/// `key`: The key buffer
/// `ret_buf`: The ret_buf buffer
fn get_value_complete(
&self,
result: Result<(), ErrorCode>,
key: &'static mut K,
ret_buf: &'static mut [u8],
);
/// This callback is called when the invalidate_key operation completes
///
/// `result`: Nothing on success, 'ErrorCode' on error
/// `key`: The key buffer
fn invalidate_key_complete(&self, result: Result<(), ErrorCode>, key: &'static mut K);
/// This callback is called when the garbage_collect operation completes
///
/// `result`: Nothing on success, 'ErrorCode' on error
fn garbage_collect_complete(&self, result: Result<(), ErrorCode>);
}
pub trait KVSystem<'a> {
/// The type of the hashed key. For example '[u8; 8]'.
type K: KeyType;
/// Set the client
fn set_client(&self, client: &'a dyn Client<Self::K>);
/// Generate key
///
/// `unhashed_key`: A unhashed key that should be hashed.
/// `key_buf`: A buffer to store the hashed key output.
///
/// On success returns nothing.
/// On error the unhashed_key, key_buf and `Result<(), ErrorCode>` will be returned.
fn generate_key(
&self,
unhashed_key: &'static mut [u8],
key_buf: &'static mut Self::K,
) -> Result<
(),
(
&'static mut [u8],
&'static mut Self::K,
Result<(), ErrorCode>,
),
>;
/// Appends the key/value pair.
///
/// `key`: A hashed key. This key will be used in future to retrieve
/// or remove the `value`.
/// `value`: A buffer containing the data to be stored to flash.
///
/// On success nothing will be returned.
/// On error the key, value and a `Result<(), ErrorCode>` will be returned.
///
/// The possible `Result<(), ErrorCode>`s are:
/// `BUSY`: An operation is already in progress
/// `INVAL`: An invalid parameter was passed
/// `NODEVICE`: No KV store was setup
/// `ENOSUPPORT`: The key could not be added due to a collision.
/// `NOMEM`: The key could not be added due to no more space.
fn append_key(
&self,
key: &'static mut Self::K,
value: &'static mut [u8],
) -> Result<
(),
(
&'static mut Self::K,
&'static mut [u8],
Result<(), ErrorCode>,
),
>;
/// Retrieves the value from a specified key.
///
/// `key`: A hashed key. This key will be used to retrieve the `value`.
/// `ret_buf`: A buffer to store the value to.
///
/// On success nothing will be returned.
/// On error the key, ret_buf and a `Result<(), ErrorCode>` will be returned.
///
/// The possible `Result<(), ErrorCode>`s are:
/// `BUSY`: An operation is already in progress
/// `INVAL`: An invalid parameter was passed
/// `NODEVICE`: No KV store was setup
/// `ENOSUPPORT`: The key could not be found.
fn get_value(
&self,
key: &'static mut Self::K,
ret_buf: &'static mut [u8],
) -> Result<
(),
(
&'static mut Self::K,
&'static mut [u8],
Result<(), ErrorCode>,
),
>;
/// Invalidates the key in flash storage
///
/// `key`: A hashed key. This key will be used to remove the `value`.
///
/// On success nothing will be returned.
/// On error the key and a `Result<(), ErrorCode>` will be returned.
///
/// The possible `Result<(), ErrorCode>`s are:
/// `BUSY`: An operation is already in progress
/// `INVAL`: An invalid parameter was passed
/// `NODEVICE`: No KV store was setup
/// `ENOSUPPORT`: The key could not be found.
fn invalidate_key(
&self,
key: &'static mut Self::K,
) -> Result<(), (&'static mut Self::K, Result<(), ErrorCode>)>;
/// Perform a garbage collection on the KV Store
///
/// For implementations that don't require garbage collecting
/// this can just be a NOP that returns 'Ok(0)'.
///
/// On success the number of bytes freed will be returned.
/// On error a `Result<(), ErrorCode>` will be returned.
///
/// The possible `Result<(), ErrorCode>`s are:
/// `BUSY`: An operation is already in progress
/// `INVAL`: An invalid parameter was passed
/// `NODEVICE`: No KV store was setup
fn garbage_collect(&self) -> Result<usize, Result<(), ErrorCode>>;
}