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# lookupItem(named:in:packer:context:replyHandler:)

Looks up an item within a directory and maps its disk space.

```
func lookupItem(named name: FSFileName, in directory: FSItem, packer: FSExtentPacker, context: FSContext, replyHandler reply: @escaping @Sendable (FSLookupItemKOIOResult?, (any Error)?) -> Void)
```

```
func lookupItem(named name: FSFileName, in directory: FSItem, packer: FSExtentPacker, context: FSContext) async throws -> FSLookupItemKOIOResult
```

## Parameters

`name`

The name of the file to look up.

`directory`

The directory in which to look up the file.

`packer`

An extent packer you use to pack the file’s allocated disk space.

`context`

An object that enables context-aware file system decisions throughout the operation.

`reply`

A block or closure to indicate success or failure. If lookup succeeds, pass an instance of [`FSLookupItemKOIOResult`](/documentation/FSKit/FSLookupItemKOIOResult) containing the found [`FSItem`](/documentation/FSKit/FSItem) together with its [`FSFileName`](/documentation/FSKit/FSFileName) (as saved within the file system) and its [`FSItem.Attributes`](/documentation/FSKit/FSItem/Attributes), along with a `nil` error. If lookup fails, pass the relevant error as the second parameter; FSKit ignores the [`FSLookupItemKOIOResult`](/documentation/FSKit/FSLookupItemKOIOResult) instance in this case. For an `async` Swift implementation, there’s no reply handler; simply return the result instance or throw an error.

## Discussion

This method allows the module to opportunistically supply extents, avoiding future calls to [`blockmapFile(_:offset:length:flags:operationID:packer:replyHandler:)`](/documentation/FSKit/FSVolume/KernelOffloadedIOHandler/blockmapFile(_:offset:length:flags:operationID:packer:replyHandler:)).
Only perform this technique opportunistically.
In particular, don’t perform additional I/O to fetch extent data.

---

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