Filing system drive information

Introduction

Filing systems may be based on devices which are able to be changed dynamically in use ('hot pluggable'). These devices may issue an UpCall to indicate that a device is now available, or has become unavailable.

Technical details

Two UpCalls are used to indicate that a filing system path residing on a device is now available, or has been made unavailable:

Not all devices and filing systems issue these UpCalls, so clients should treat them as advisory.

UpCalls

UpCall_DriveAddedUpCall &18
A filing system may be available on a given path.
R0=24 (&18)
R1=Pointer to a zero-terminated filing system path prefix for a new device
R0 - R1preserved

This UpCall is issued by a device when filing system path has been made available. This may happen due to a new disc being inserted, a device being formatted, or a remote system becoming available.

At the time that the UpCall is issued the filing system path should be accessible through normal filing system operations. The nature of hot pluggable systems mean that by the time this call is received, the device may have already become unavailable, or the filing system on the device may not be present.

The filing system path takes the form of a filing system name, a disc name specification and an optional path specification. For some devices, the disc name may be a number, indicating that no name has been determined yet, or that there is no name available. For others, a name may be given. It is recommended that the path be canonicalised to obtain the correct name of the device.

Example prefix names:

  • ADFS::4
  • SDFS::0
  • Share::Storage
  • HostFS::Host.$.Mountpoint

This UpCall must not be claimed.

UpCall_DriveRemoved
UpCall_DriveRemovedUpCall &19
A filing system is no longer available on a given path.
R0=25 (&19)
R1=Pointer to a zero-terminated filing system path prefix for a new device
R0 - R1preserved

This UpCall is issued by a device when filing system path is no longer available. This may happen due to a disc being removed, a device being formatted, or a remote system becoming unavailable.

At the time that the UpCall is issued the filing system path will not be accessible and no further information is available. As such, clients should attempt to track the paths to which the drive may refer. In particular, devices may refer to drive numbers, without any name being canonicalised, and clients may therefore need to track which drive numbers refer to which canonicalised disc names.

This UpCall must not be claimed.

UpCall_DriveAdded