---
title: genPhysicalSegments
framework: kernel
role: pseudoSymbol
path: kernel/iomemorycursor/1812441-genphysicalsegments
---

# genPhysicalSegments

Generates a physical scatter/gather list given a memory descriptor.

## Declaration

```occ
virtual UInt32 genPhysicalSegments( 
 IOMemoryDescriptor *descriptor, 
 IOByteCount fromPosition, 
 void *segments, 
 UInt32 maxSegments, 
 UInt32 maxTransferSize = 0, 
 IOByteCount *transferSize = 0); 
```

## Parameters

- `descriptor`: IOMemoryDescriptor that describes the data associated with an I/O request.
- `fromPosition`: Starting location of the I/O within a memory descriptor.
- `segments`: Void pointer to base of output physical scatter/gather list. Always passed directly onto the SegmentFunction without interpretation by the cursor.
- `maxSegments`: Maximum number of segments that can be written to segments array.
- `maxTransferSize`: Maximum transfer size is limited to that many bytes, otherwise it defaults to the maximum transfer size specified when the memory cursor was initialized.
- `transferSize`: Pointer to an IOByteCount variable that can contain the total size of the transfer being described. Defaults to 0 indicating that no transfer size need be returned.

## Return Value

Return Value If the descriptor is exhausted of memory, a zero is returned, otherwise the number of segments that were filled in is returned.

## Overview

Overview Generates a list of physical segments from the given memory descriptor, relative to the current position of the descriptor.

## See Also

### Miscellaneous

- [initWithSpecification](kernel/iomemorycursor/1812445-initwithspecification.md)
- [withSpecification](kernel/iomemorycursor/1812453-withspecification.md)