Re: [PATCH 3/3] scsi_lib: Collapse scsi_end_request into only user

[Matthew Wilcox <matthew@wil.cx>]

On Mon, Jan 04, 2010 at 02:17:06PM +0200, Boaz Harrosh wrote:
> Embedding scsi_end_request() into scsi_io_completion actually simplifies the
> code and makes it clearer what's going on.

I'm not entirely convinced about that -- scsi_io_completion is currently
over 200 lines long and needs to be made shorter, not longer.  That said,
I see no reason that the current factoring of scsi_io_completion() makes
sense; pushing the decoding of the sense key into a separate function
looks like a more profitable idea.  It would also let you do without
the nasty gotos you add in this patch.

> There is absolutely no functional and/or side effects changes after this patch.
> 
> Patch was inspired by Alan Stern.
> 
> CC: Alan Stern <stern@rowland.harvard.edu>
> Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
> ---
>  drivers/scsi/scsi_lib.c |   90 +++++++++++-----------------------------------
>  1 files changed, 22 insertions(+), 68 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 8d8b4eb..326b228 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -512,66 +512,6 @@ void scsi_run_host_queues(struct Scsi_Host *shost)
>  		scsi_run_queue(sdev->request_queue);
>  }
>  
> -/*
> - * Function:    scsi_end_request()
> - *
> - * Purpose:     Post-processing of completed commands (usually invoked at end
> - *		of upper level post-processing and scsi_io_completion).
> - *
> - * Arguments:   cmd	 - command that is complete.
> - *              error    - 0 if I/O indicates success, < 0 for I/O error.
> - *              bytes    - number of bytes of completed I/O
> - *		requeue  - indicates whether we should requeue leftovers.
> - *
> - * Lock status: Assumed that lock is not held upon entry.
> - *
> - * Returns:     cmd if requeue required, NULL otherwise.
> - *
> - * Notes:       This is called for block device requests in order to
> - *              mark some number of sectors as complete.
> - * 
> - *		We are guaranteeing that the request queue will be goosed
> - *		at some point during this call.
> - * Notes:	If cmd was requeued, upon return it will be a stale pointer.
> - */
> -static struct scsi_cmnd *scsi_end_request(struct scsi_cmnd *cmd, int error,
> -					  int bytes, int requeue)
> -{
> -	struct request *req = cmd->request;
> -
> -	/*
> -	 * If there are blocks left over at the end, set up the command
> -	 * to queue the remainder of them.
> -	 */
> -	if (blk_end_request(req, error, bytes)) {
> -		/* kill remainder if no retrys */
> -		if (error && scsi_noretry_cmd(cmd))
> -			blk_end_request_all(req, error);
> -		else {
> -			if (requeue) {
> -				/*
> -				 * Bleah.  Leftovers again.  Stick the
> -				 * leftovers in the front of the
> -				 * queue, and goose the queue again.
> -				 */
> -				scsi_release_buffers(cmd);
> -				scsi_requeue_command(cmd);
> -				cmd = NULL;
> -			}
> -			return cmd;
> -		}
> -	}
> -
> -	cmd->request = NULL;
> -	/*
> -	 * This will goose the queue request function at the end, so we don't
> -	 * need to worry about launching another command.
> -	 */
> -	scsi_release_buffers(cmd);
> -	scsi_next_command(cmd);
> -	return NULL;
> -}
> -
>  static inline unsigned int scsi_sgtable_index(unsigned short nents)
>  {
>  	unsigned int index;
> @@ -704,7 +644,7 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
>  	struct scsi_sense_hdr sshdr;
>  	int sense_valid = 0;
>  	int sense_deferred = 0;
> -	enum {ACTION_FAIL, ACTION_REPREP, ACTION_RETRY,
> +	enum {ACTION_FAIL, ACTION_REPREP, ACTION_NEXT_CMND, ACTION_RETRY,
>  	      ACTION_DELAYED_RETRY} action;
>  	char *description = NULL;
>  
> @@ -773,13 +713,22 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
>  		error = 0;
>  	}
>  
> -	/*
> -	 * A number of bytes were successfully read.  If there
> -	 * are leftovers and there is some kind of error
> -	 * (result != 0), retry the rest.
> -	 */
> -	if (scsi_end_request(cmd, error, good_bytes, result == 0) == NULL)
> -		return;
> +	if (!blk_end_request(req, error, good_bytes)) {
> +		cmd->request = NULL;
> +		action = ACTION_NEXT_CMND;
> +		goto do_action;
> +	}
> +
> +	if (error && scsi_noretry_cmd(cmd)) {
> +		/* kill remainder if no retrys */
> +		blk_end_request_all(req, error);
> +		cmd->request = NULL;
> +		action = ACTION_NEXT_CMND;
> +		goto do_action;
> +	} else if (result == 0) {
> +		action = ACTION_REPREP;
> +		goto do_action;
> +	}
>  
>  	error = -EIO;
>  
> @@ -878,6 +827,7 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
>  		action = ACTION_FAIL;
>  	}
>  
> +do_action:
>  	switch (action) {
>  	case ACTION_FAIL:
>  		/* Give up and fail the remainder of the request */
> @@ -896,6 +846,10 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
>  		else
>  			scsi_next_command(cmd);
>  		break;
> +	case ACTION_NEXT_CMND:
> +		scsi_release_buffers(cmd);
> +		scsi_next_command(cmd);
> +		break;
>  	case ACTION_REPREP:
>  		/* Unprep the request and put it back at the head of the queue.
>  		 * A new command will be prepared and issued.
> -- 
> 1.6.6
> 
> 
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-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."