Trait LayerIo

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pub trait LayerIo:
    'static
    + Send
    + Sync
    + Inspect {
Show 15 methods    // Required methods
    fn layer_type(&self) -> &str;
    fn sector_count(&self) -> u64;
    fn sector_size(&self) -> u32;
    fn disk_id(&self) -> Option<[u8; 16]>;
    fn physical_sector_size(&self) -> u32;
    fn is_fua_respected(&self) -> bool;
    fn is_logically_read_only(&self) -> bool;
    fn sync_cache(&self) -> impl Future<Output = Result<(), DiskError>> + Send;
    fn read(
        &self,
        buffers: &RequestBuffers<'_>,
        sector: u64,
        marker: SectorMarker<'_>,
    ) -> impl Future<Output = Result<(), DiskError>> + Send;
    fn write(
        &self,
        buffers: &RequestBuffers<'_>,
        sector: u64,
        fua: bool,
    ) -> impl Future<Output = Result<(), DiskError>> + Send;
    fn unmap(
        &self,
        sector: u64,
        count: u64,
        block_level_only: bool,
        next_is_zero: bool,
    ) -> impl Future<Output = Result<(), DiskError>> + Send;
    fn unmap_behavior(&self) -> UnmapBehavior;

    // Provided methods
    fn optimal_unmap_sectors(&self) -> u32 { ... }
    fn write_no_overwrite(&self) -> Option<impl WriteNoOverwrite> { ... }
    fn wait_resize(&self, sector_count: u64) -> impl Future<Output = u64> + Send { ... }
}

Expand description

Metadata and IO for disk layers.

Required Methods§

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fn layer_type(&self) -> &str

Returns the layer type name as a string.

This is used for diagnostic purposes.

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fn sector_count(&self) -> u64

Returns the current sector count.

For some backing stores, this may change at runtime. If it does, then the backing store must also implement [DiskIo::wait_resize].

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fn sector_size(&self) -> u32

Returns the logical sector size of the backing store.

This must not change at runtime.

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fn disk_id(&self) -> Option<[u8; 16]>

Optionally returns a 16-byte identifier for the disk, if there is a natural one for this backing store.

This may be exposed to the guest as a unique disk identifier. This must not change at runtime.

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fn physical_sector_size(&self) -> u32

Returns the physical sector size of the backing store.

This must not change at runtime.

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fn is_fua_respected(&self) -> bool

Returns true if the fua parameter to LayerIo::write is respected by the backing store by ensuring that the IO is immediately committed to disk.

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fn is_logically_read_only(&self) -> bool

Returns true if the layer is logically read only.

If this returns true, the layer might still be writable via write_no_overwrite, used to populate the layer as a read cache.

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fn sync_cache(&self) -> impl Future<Output = Result<(), DiskError>> + Send

Issues an asynchronous flush operation to the disk.

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fn read( &self, buffers: &RequestBuffers<'_>, sector: u64, marker: SectorMarker<'_>, ) -> impl Future<Output = Result<(), DiskError>> + Send

Reads sectors from the layer.

marker is used to specify which sectors have been read. Those that are not read will be passed to the next layer, or zeroed if there are no more layers.

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fn write( &self, buffers: &RequestBuffers<'_>, sector: u64, fua: bool, ) -> impl Future<Output = Result<(), DiskError>> + Send

Writes sectors to the layer.

§Panics

The caller must pass a buffer with an integer number of sectors.

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fn unmap( &self, sector: u64, count: u64, block_level_only: bool, next_is_zero: bool, ) -> impl Future<Output = Result<(), DiskError>> + Send

Unmap sectors from the layer.

If next_is_zero is true, then the next layer’s content’s are known to be zero. A layer can use this information to just discard the sectors rather than putting them in the zero state (which make take more space).

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