66 lines
2.2 KiB
Go
66 lines
2.2 KiB
Go
|
package meta
|
||
|
|
|
||
|
|
import (
|
||
|
|
"fmt"
|
||
|
|
|
||
|
|
chunkmeta "git.keganmyers.com/terribleplan/file-store/pkg/chunk/meta"
|
||
|
|
"git.keganmyers.com/terribleplan/file-store/pkg/util"
|
||
|
|
)
|
||
|
|
|
||
|
|
type Params struct {
|
||
|
|
Size int64 `json:"s,string"`
|
||
|
|
Stride int32 `json:"t"`
|
||
|
|
Shards uint16 `json:"h"`
|
||
|
|
Parity uint16 `json:"p"`
|
||
|
|
}
|
||
|
|
|
||
|
|
func (params Params) Plan(offset, size int64) []chunkmeta.ShardMeta {
|
||
|
|
outputs := []chunkmeta.ShardMeta{}
|
||
|
|
end := offset + size
|
||
|
|
if (end - 1) > params.Size {
|
||
|
|
panic(fmt.Errorf("attempted read beyond end of file"))
|
||
|
|
}
|
||
|
|
// constant
|
||
|
|
shards := int64(params.Shards)
|
||
|
|
baseStride := int64(params.Stride)
|
||
|
|
baseStripeWidth := baseStride * shards
|
||
|
|
|
||
|
|
oddStripeOffset := (params.Size / baseStripeWidth) * baseStripeWidth
|
||
|
|
oddChunkOffset := oddStripeOffset / shards
|
||
|
|
oddSize := (params.Size - oddStripeOffset)
|
||
|
|
oddStride := oddSize / shards
|
||
|
|
if oddSize%shards > 0 {
|
||
|
|
oddStride += 1
|
||
|
|
}
|
||
|
|
|
||
|
|
for offset < end {
|
||
|
|
output := chunkmeta.ShardMeta{GlobalOffset: offset}
|
||
|
|
// var chunk uint64 // which chunk the shard is in
|
||
|
|
// var chunkOffset uint64 // the location within the chunk that the shard begins
|
||
|
|
// var shardOffset uint64 // the location within the shard at which the data begins
|
||
|
|
// var readSize uint64 // the number of bytes to read from the shard
|
||
|
|
|
||
|
|
if offset >= oddStripeOffset {
|
||
|
|
localOffset := offset - oddStripeOffset // the location relative to the odd data at which the desired data begins
|
||
|
|
output.Chunk = uint16(localOffset / oddStride)
|
||
|
|
output.Shard = uint16(oddStripeOffset/baseStride) + output.Chunk
|
||
|
|
output.ShardOffset = localOffset % oddStride
|
||
|
|
output.ChunkOffset = oddChunkOffset + output.ShardOffset
|
||
|
|
output.Size = int32(util.Min(end-offset, oddStride-output.ShardOffset))
|
||
|
|
} else {
|
||
|
|
shard := offset / baseStride
|
||
|
|
output.Shard = uint16(offset / baseStride) // which shard the data is in
|
||
|
|
output.Chunk = uint16(shard % shards)
|
||
|
|
output.ShardOffset = offset % baseStride
|
||
|
|
output.ChunkOffset = ((shard / shards) * baseStride) + output.ShardOffset
|
||
|
|
output.Size = int32(util.Min(end-offset, baseStride-output.ShardOffset))
|
||
|
|
}
|
||
|
|
if output.Size <= 0 {
|
||
|
|
panic(fmt.Errorf("invalid read size"))
|
||
|
|
}
|
||
|
|
outputs = append(outputs, output)
|
||
|
|
offset += int64(output.Size)
|
||
|
|
}
|
||
|
|
return outputs
|
||
|
|
}
|