Types
In the case of an upgrade,
OldVsn
is
Vsn
, and in the case of a downgrade,
OldVsn
is
{down,Vsn}
.
Vsn
is defined by the
vsn
attribute(s) of the old version of the callback module
Module
. If no such attribute is defined, the version is the checksum of the BEAM file.
Internal state of the channel.
Passed "as-is" from the
{advanced,Extra}
part of the update instruction.
Converts process state when code is changed.
This function is called by a client-side channel when it is to update its internal state during a release upgrade or downgrade, that is, when the instruction {update,Module,Change,...}
, where Change={advanced,Extra}
, is given in the appup
file. For more information, refer to Section 9.11.6 Release Handling Instructions in the System Documentation
.
Note
Soft upgrade according to the OTP release concept is not straight forward for the server side, as subsystem channel processes are spawned by the ssh
application and hence added to its supervisor tree. The subsystem channels can be upgraded when upgrading the user application, if the callback functions can handle two versions of the state, but this function cannot be used in the normal way.