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Free chunk list

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~erin 2023-04-20 17:26:40 -04:00
parent af21da0fe1
commit e70be2c638
Signed by untrusted user: erin
GPG Key ID: 9A8E308CEFA37A47
1 changed files with 13 additions and 5 deletions
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18
src/development/design/filesystem.md
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@ -105,7 +105,7 @@ Also, we are able to verify data. Before passing off the data, we re-hash it usi
If it does, we simply pass it along like normal. If not, we refuse, and send an error [message](/development/design/actor.md#messages). If it does, we simply pass it along like normal. If not, we refuse, and send an error [message](/development/design/actor.md#messages).
### Writing ### Writing
Writing uses a similar process. An *Actor* can request to write data. If it has proper capabilties, we serialize the data, allocate a free chunk[^free_chunk], and write to it. Writing uses a similar process. An *Actor* can request to write data. If it has proper capabilties, we serialize the data, allocate a free chunk, and write to it.
We *hash* the data first to generate a checksum, and set proper metadata. We *hash* the data first to generate a checksum, and set proper metadata.
### Permissions ### Permissions
@ -119,12 +119,15 @@ will be determined via [capabilities](/development/design/actor.md#ocap)
### Indexing ### Indexing
Created in-memory on startup, modified directly whenever the filesystem is modified. Created in-memory on startup, modified directly whenever the filesystem is modified.
It's saved in the *Index Sector* (which is at a known offset), allowing it to be read in easily on boot. It's saved in the *Index Sector* (which is at a known offset), allowing it to be read in easily on boot.
It again simply uses `bincode` and compression.
The index is simply an `alloc::` [BTreeMap](https://doc.rust-lang.org/stable/alloc/collections/btree_map/struct.BTreeMap.html). The index is simply an `alloc::` [BTreeMap](https://doc.rust-lang.org/stable/alloc/collections/btree_map/struct.BTreeMap.html).
We also have a simple `Vec` of the chunks that are free, which we modify in reverse.
```rust ```rust
let mut index = BTreeMap::new(); let mut index = BTreeMap::new(); // Basic Actor index
let mut free_index = Vec<u64>; // Index of free chunks
struct Location { struct Location {
partition: Uuid, // Partition identified via Uuid partition: Uuid, // Partition identified via Uuid
chunks: Vec<u64>, // Which chunk(s) in the partition it is chunks: Vec<u64>, // Which chunk(s) in the partition it is
@ -136,9 +139,16 @@ let new_data_location = Location {
} }
index.entry(&actor.uuid).or_insert(&new_data_location); // Insert an Actor's storage location if it's not already stored index.entry(&actor.uuid).or_insert(&new_data_location); // Insert an Actor's storage location if it's not already stored
for i in &new_data_location.chunks {
free_index.pop(&i); // Remove used chunks from the free chunks list
}
index.contains_key(&actor.uuid); // Check if the index contains an Actor's data index.contains_key(&actor.uuid); // Check if the index contains an Actor's data
index.get(&actor.uuid); // Get the Location of the actor index.get(&actor.uuid); // Get the Location of the actor
index.remove(&actor.uuid); // Remove an Actor's data from the index (e.g. on deletion) index.remove(&actor.uuid); // Remove an Actor's data from the index (e.g. on deletion)
for i in &new_data_location.chunks {
free_index.push(&i); // Add back the now free chunks
}
``` ```
This then allows the index to be searched easily to find the data location of a specific `Uuid`. This then allows the index to be searched easily to find the data location of a specific `Uuid`.
@ -179,5 +189,3 @@ struct PackedExecutable {
``` ```
[^encryption]: Specific details to be figured out later [^encryption]: Specific details to be figured out later
[^free_chunk]: Need to figure out how to efficiently do this. **XFS** seems to just keep another index of free chunks. It also uses a **B+Tree** rather than a hashmap - to look into.