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/*
* scsi_queue.c Copyright (C) 1997 Eric Youngdale
*
* generic mid-level SCSI queueing.
*
* The point of this is that we need to track when hosts are unable to
* accept a command because they are busy. In addition, we track devices
* that cannot accept a command because of a QUEUE_FULL condition. In both
* of these cases, we enter the command in the queue. At some later point,
* we attempt to remove commands from the queue and retry them.
*/
#define __NO_VERSION__
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/ioport.h>
#include <linux/kernel.h>
#include <linux/stat.h>
#include <linux/blk.h>
#include <linux/interrupt.h>
#include <linux/delay.h>
#include <linux/smp_lock.h>
#define __KERNEL_SYSCALLS__
#include <linux/unistd.h>
#include <asm/system.h>
#include <asm/irq.h>
#include <asm/dma.h>
#include "scsi.h"
#include "hosts.h"
#include "constants.h"
/*
* TODO:
* 1) Prevent multiple traversals of list to look for commands to
* queue.
* 2) Protect against multiple insertions of list at the same time.
* DONE:
* 1) Set state of scsi command to a new state value for ml queue.
* 2) Insert into queue when host rejects command.
* 3) Make sure status code is properly passed from low-level queue func
* so that internal_cmnd properly returns the right value.
* 4) Insert into queue when QUEUE_FULL.
* 5) Cull queue in bottom half handler.
* 6) Check usage count prior to queue insertion. Requeue if usage
* count is 0.
* 7) Don't send down any more commands if the host/device is busy.
*/
static const char RCSid[] = "$Header: /mnt/ide/home/eric/CVSROOT/linux/drivers/scsi/scsi_queue.c,v 1.1 1997/10/21 11:16:38 eric Exp $";
/*
* Function: scsi_mlqueue_insert()
*
* Purpose: Insert a command in the midlevel queue.
*
* Arguments: cmd - command that we are adding to queue.
* reason - why we are inserting command to queue.
*
* Lock status: Assumed that lock is not held upon entry.
*
* Returns: Nothing.
*
* Notes: We do this for one of two cases. Either the host is busy
* and it cannot accept any more commands for the time being,
* or the device returned QUEUE_FULL and can accept no more
* commands.
* Notes: This could be called either from an interrupt context or a
* normal process context.
*/
int scsi_mlqueue_insert(Scsi_Cmnd * cmd, int reason)
{
struct Scsi_Host *host;
unsigned long flags;
SCSI_LOG_MLQUEUE(1, printk("Inserting command %p into mlqueue\n", cmd));
/*
* We are inserting the command into the ml queue. First, we
* cancel the timer, so it doesn't time out.
*/
scsi_delete_timer(cmd);
host = cmd->host;
/*
* Next, set the appropriate busy bit for the device/host.
*/
if (reason == SCSI_MLQUEUE_HOST_BUSY) {
/*
* Protect against race conditions. If the host isn't busy,
* assume that something actually completed, and that we should
* be able to queue a command now. Note that there is an implicit
* assumption that every host can always queue at least one command.
* If a host is inactive and cannot queue any commands, I don't see
* how things could possibly work anyways.
*/
if (host->host_busy == 0) {
if (scsi_retry_command(cmd) == 0) {
return 0;
}
}
host->host_blocked = TRUE;
} else {
/*
* Protect against race conditions. If the device isn't busy,
* assume that something actually completed, and that we should
* be able to queue a command now. Note that there is an implicit
* assumption that every host can always queue at least one command.
* If a host is inactive and cannot queue any commands, I don't see
* how things could possibly work anyways.
*/
if (cmd->device->device_busy == 0) {
if (scsi_retry_command(cmd) == 0) {
return 0;
}
}
cmd->device->device_blocked = TRUE;
}
/*
* Register the fact that we own the thing for now.
*/
cmd->state = SCSI_STATE_MLQUEUE;
cmd->owner = SCSI_OWNER_MIDLEVEL;
cmd->bh_next = NULL;
/*
* Decrement the counters, since these commands are no longer
* active on the host/device.
*/
spin_lock_irqsave(&io_request_lock, flags);
cmd->host->host_busy--;
cmd->device->device_busy--;
spin_unlock_irqrestore(&io_request_lock, flags);
/*
* Insert this command at the head of the queue for it's device.
* It will go before all other commands that are already in the queue.
*/
scsi_insert_special_cmd(cmd, 1);
return 0;
}
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