Commit 14cf42d2 authored by James Bottomley's avatar James Bottomley Committed by James Bottomley

[PATCH] scsi_mid_low_api.txt update to clarify queuecommand return values

The only documentation about the MLQUEUE returns is in the code, it
should also be in here.
parent db28b79c
......@@ -1091,14 +1091,44 @@ Details:
* @scp: pointer to scsi command object
* @done: function pointer to be invoked on completion
*
* Returns 0 on success and 1 if the LLD or the HBA is busy (i.e. run
* out of resources to queue further commands). Other types of errors
* that are detected immediately are flagged by setting scp->result
* to an appropriate value, invoking the 'done' callback, and then
* returning 0 from this function. If the command is not performed
* immediately (and the LLD is starting (or will start) the given
* command) then this function should place 0 in scp->result and
* return 0.
* Returns 0 on success.
*
* If there's a failure, return either:
*
* SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or
* SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full
*
* On both of these returns, the mid-layer will requeue the I/O
*
* - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular
* device will be paused, and it will be unpaused when a command to
* the device returns (or after a brief delay if there are no more
* outstanding commands to it). Commands to other devices continue
* to be processed normally.
*
* - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host
* is paused and will be unpaused when any command returns from
* the host (or after a brief delay if there are no outstanding
* commands to the host).
*
* For compatibility with earlier versions of queuecommand, any
* other return value is treated the same as
* SCSI_MLQUEUE_HOST_BUSY.
*
* Other types of errors that are detected immediately may be
* flagged by setting scp->result to an appropriate value,
* invoking the 'done' callback, and then returning 0 from this
* function. If the command is not performed immediately (and the
* LLD is starting (or will start) the given command) then this
* function should place 0 in scp->result and return 0.
*
* Command ownership. If the driver returns zero, it owns the
* command and must take responsibility for ensuring the 'done'
* callback is executed. Note: the driver may call done before
* returning zero, but after it has called done, it may not
* return any value other than zero. If the driver makes a
* non-zero return, it must not execute the command's done
* callback at any time.
*
* Locks: struct Scsi_Host::host_lock held on entry (with "irqsave")
* and is expected to be held on return.
......
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