hd: dequeue and track in-flight request

hd has at most single request in flight.  Till now, whenever it needs
to access the in-flight request it called elv_next_request().  This
patch makes hd track the in-flight request directly and dequeue it
when processing starts.  The added complexity is minimal and this will
help future block layer changes.

[ Impact: dequeue in-flight request, one elv_next_request() per request ]

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/drivers/block/hd.c b/drivers/block/hd.c
index a3b3994..288ab63 100644 (file)
--- a/drivers/block/hd.c
+++ b/drivers/block/hd.c
@@ -98,10 +98,9 @@
 
 static DEFINE_SPINLOCK(hd_lock);
 static struct request_queue *hd_queue;
+static struct request *hd_req;
 
 #define MAJOR_NR HD_MAJOR
-#define QUEUE (hd_queue)
-#define CURRENT elv_next_request(hd_queue)
 
 #define TIMEOUT_VALUE  (6*HZ)
 #define        HD_DELAY        0
@@ -195,11 +194,24 @@ static void __init hd_setup(char *str, int *ints)
        NR_HD = hdind+1;
 }
 
+static bool hd_end_request(int err, unsigned int bytes)
+{
+       if (__blk_end_request(hd_req, err, bytes))
+               return true;
+       hd_req = NULL;
+       return false;
+}
+
+static bool hd_end_request_cur(int err)
+{
+       return hd_end_request(err, blk_rq_cur_bytes(hd_req));
+}
+
 static void dump_status(const char *msg, unsigned int stat)
 {
        char *name = "hd?";
-       if (CURRENT)
-               name = CURRENT->rq_disk->disk_name;
+       if (hd_req)
+               name = hd_req->rq_disk->disk_name;
 
 #ifdef VERBOSE_ERRORS
        printk("%s: %s: status=0x%02x { ", name, msg, stat & 0xff);
@@ -227,8 +239,8 @@ static void dump_status(const char *msg, unsigned int stat)
                if (hd_error & (BBD_ERR|ECC_ERR|ID_ERR|MARK_ERR)) {
                        printk(", CHS=%d/%d/%d", (inb(HD_HCYL)<<8) + inb(HD_LCYL),
                                inb(HD_CURRENT) & 0xf, inb(HD_SECTOR));
-                       if (CURRENT)
-                               printk(", sector=%ld", blk_rq_pos(CURRENT));
+                       if (hd_req)
+                               printk(", sector=%ld", blk_rq_pos(hd_req));
                }
                printk("\n");
        }
@@ -406,11 +418,12 @@ static void unexpected_hd_interrupt(void)
  */
 static void bad_rw_intr(void)
 {
-       struct request *req = CURRENT;
+       struct request *req = hd_req;
+
        if (req != NULL) {
                struct hd_i_struct *disk = req->rq_disk->private_data;
                if (++req->errors >= MAX_ERRORS || (hd_error & BBD_ERR)) {
-                       __blk_end_request_cur(req, -EIO);
+                       hd_end_request_cur(-EIO);
                        disk->special_op = disk->recalibrate = 1;
                } else if (req->errors % RESET_FREQ == 0)
                        reset = 1;
@@ -454,14 +467,14 @@ static void read_intr(void)
        return;
 
 ok_to_read:
-       req = CURRENT;
+       req = hd_req;
        insw(HD_DATA, req->buffer, 256);
 #ifdef DEBUG
        printk("%s: read: sector %ld, remaining = %u, buffer=%p\n",
               req->rq_disk->disk_name, blk_rq_pos(req) + 1,
               blk_rq_sectors(req) - 1, req->buffer+512);
 #endif
-       if (__blk_end_request(req, 0, 512)) {
+       if (hd_end_request(0, 512)) {
                SET_HANDLER(&read_intr);
                return;
        }
@@ -475,7 +488,7 @@ ok_to_read:
 
 static void write_intr(void)
 {
-       struct request *req = CURRENT;
+       struct request *req = hd_req;
        int i;
        int retries = 100000;
 
@@ -494,7 +507,7 @@ static void write_intr(void)
        return;
 
 ok_to_write:
-       if (__blk_end_request(req, 0, 512)) {
+       if (hd_end_request(0, 512)) {
                SET_HANDLER(&write_intr);
                outsw(HD_DATA, req->buffer, 256);
                return;
@@ -525,18 +538,18 @@ static void hd_times_out(unsigned long dummy)
 
        do_hd = NULL;
 
-       if (!CURRENT)
+       if (!hd_req)
                return;
 
        spin_lock_irq(hd_queue->queue_lock);
        reset = 1;
-       name = CURRENT->rq_disk->disk_name;
+       name = hd_req->rq_disk->disk_name;
        printk("%s: timeout\n", name);
-       if (++CURRENT->errors >= MAX_ERRORS) {
+       if (++hd_req->errors >= MAX_ERRORS) {
 #ifdef DEBUG
                printk("%s: too many errors\n", name);
 #endif
-               __blk_end_request_cur(CURRENT, -EIO);
+               hd_end_request_cur(-EIO);
        }
        hd_request();
        spin_unlock_irq(hd_queue->queue_lock);
@@ -551,7 +564,7 @@ static int do_special_op(struct hd_i_struct *disk, struct request *req)
        }
        if (disk->head > 16) {
                printk("%s: cannot handle device with more than 16 heads - giving up\n", req->rq_disk->disk_name);
-               __blk_end_request_cur(req, -EIO);
+               hd_end_request_cur(-EIO);
        }
        disk->special_op = 0;
        return 1;
@@ -578,11 +591,15 @@ static void hd_request(void)
 repeat:
        del_timer(&device_timer);
 
-       req = CURRENT;
-       if (!req) {
-               do_hd = NULL;
-               return;
+       if (!hd_req) {
+               hd_req = elv_next_request(hd_queue);
+               if (!hd_req) {
+                       do_hd = NULL;
+                       return;
+               }
+               blkdev_dequeue_request(hd_req);
        }
+       req = hd_req;
 
        if (reset) {
                reset_hd();
@@ -595,7 +612,7 @@ repeat:
            ((block+nsect) > get_capacity(req->rq_disk))) {
                printk("%s: bad access: block=%d, count=%d\n",
                        req->rq_disk->disk_name, block, nsect);
-               __blk_end_request_cur(req, -EIO);
+               hd_end_request_cur(-EIO);
                goto repeat;
        }
 
@@ -635,7 +652,7 @@ repeat:
                        break;
                default:
                        printk("unknown hd-command\n");
-                       __blk_end_request_cur(req, -EIO);
+                       hd_end_request_cur(-EIO);
                        break;
                }
        }