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Facilitating transport mode input/output operations between a channel subsystem and input/output devices

  • US 8,631,175 B2
  • Filed: 02/28/2013
  • Issued: 01/14/2014
  • Est. Priority Date: 06/30/2011
  • Status: Active Grant
First Claim
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1. A method of performing an input/output (I/O) operation initiated by an I/O operation instruction at a host computer system configured for communication with a control unit, the control unit in communication with one or more devices, the method comprising:

  • generating at least one command message specifying an I/O operation by a channel subsystem of the host computer system, the at least one command message including one or more device command words (DCWs), each DCW associated with an I/O command, wherein at least one DCW of the one or more DCWs includes a data count and a suppress-length indication (SLI), the SLI configured to instruct a control unit whether to continue to perform the I/O operation in response to the control unit detecting an incorrect length condition, the incorrect length condition detected in response to the data count not matching an amount of data required to perform the I/O operation command, wherein the data required is one of data available at the control unit for a read operation command and data required by the control unit for a write operation command;

    forwarding the at least one command message to the control unit;

    receiving an incorrect length (IL) value from the control unit, the IL value being a first IL value in response to the SLI being a first SLI value and the data count not matching the amount of data required, the IL value being a second IL value in response to the SLI being a second SLI value and the data count not matching the amount of data required; and

    responsive to receiving the IL value from the control unit, storing an IL indicator in a subchannel-status word, the IL indicator representing the IL value.

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