[PATCH] Add scatter-gather support for the block layer SG_IO

Signed-off-by: Jens Axboe <axboe@suse.de>

2 files changed, 81 insertions, 17 deletions

diff --git a/drivers/block/ll_rw_blk.c b/drivers/block/ll_rw_blk.c
index 42c4f3651cf8..874e46fc3748 100644
--- a/drivers/block/ll_rw_blk.c
+++ b/drivers/block/ll_rw_blk.c
@@ -2149,6 +2149,50 @@ int blk_rq_map_user(request_queue_t *q, struct request *rq, void __user *ubuf,
 EXPORT_SYMBOL(blk_rq_map_user);
 
 /**
+ * blk_rq_map_user_iov - map user data to a request, for REQ_BLOCK_PC usage
+ * @q:          request queue where request should be inserted
+ * @rq:         request to map data to
+ * @iov:        pointer to the iovec
+ * @iov_count:  number of elements in the iovec
+ *
+ * Description:
+ *    Data will be mapped directly for zero copy io, if possible. Otherwise
+ *    a kernel bounce buffer is used.
+ *
+ *    A matching blk_rq_unmap_user() must be issued at the end of io, while
+ *    still in process context.
+ *
+ *    Note: The mapped bio may need to be bounced through blk_queue_bounce()
+ *    before being submitted to the device, as pages mapped may be out of
+ *    reach. It's the callers responsibility to make sure this happens. The
+ *    original bio must be passed back in to blk_rq_unmap_user() for proper
+ *    unmapping.
+ */
+int blk_rq_map_user_iov(request_queue_t *q, struct request *rq,
+                        struct sg_iovec *iov, int iov_count)
+{
+        struct bio *bio;
+
+        if (!iov || iov_count <= 0)
+                return -EINVAL;
+
+        /* we don't allow misaligned data like bio_map_user() does.  If the
+         * user is using sg, they're expected to know the alignment constraints
+         * and respect them accordingly */
+        bio = bio_map_user_iov(q, NULL, iov, iov_count, rq_data_dir(rq)== READ);
+        if (IS_ERR(bio))
+                return PTR_ERR(bio);
+
+        rq->bio = rq->biotail = bio;
+        blk_rq_bio_prep(q, rq, bio);
+        rq->buffer = rq->data = NULL;
+        rq->data_len = bio->bi_size;
+        return 0;
+}
+
+EXPORT_SYMBOL(blk_rq_map_user_iov);
+
+/**
  * blk_rq_unmap_user - unmap a request with user data
  * @rq:         request to be unmapped
  * @bio:        bio for the request
@@ -2207,6 +2251,19 @@ int blk_rq_map_kern(request_queue_t *q, struct request *rq, void *kbuf,
 
 EXPORT_SYMBOL(blk_rq_map_kern);
 
+void blk_execute_rq_nowait(request_queue_t *q, struct gendisk *bd_disk,
+                           struct request *rq, int at_head,
+                           void (*done)(struct request *))
+{
+        int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
+
+        rq->rq_disk = bd_disk;
+        rq->flags |= REQ_NOMERGE;
+        rq->end_io = done;
+        elv_add_request(q, rq, where, 1);
+        generic_unplug_device(q);
+}
+
 /**
  * blk_execute_rq - insert a request into queue for execution
  * @q:          queue to insert the request in
@@ -2224,8 +2281,6 @@ int blk_execute_rq(request_queue_t *q, struct gendisk *bd_disk,
         char sense[SCSI_SENSE_BUFFERSIZE];
         int err = 0;
 
-        rq->rq_disk = bd_disk;
-
         /*
          * we need an extra reference to the request, so we can look at
          * it after io completion
@@ -2238,11 +2293,8 @@ int blk_execute_rq(request_queue_t *q, struct gendisk *bd_disk,
                 rq->sense_len = 0;
         }
 
-        rq->flags |= REQ_NOMERGE;
         rq->waiting = &wait;
-        rq->end_io = blk_end_sync_rq;
-        elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 1);
-        generic_unplug_device(q);
+        blk_execute_rq_nowait(q, bd_disk, rq, 0, blk_end_sync_rq);
         wait_for_completion(&wait);
         rq->waiting = NULL;
 
diff --git a/drivers/block/scsi_ioctl.c b/drivers/block/scsi_ioctl.c
index 93c4ca874be3..09a7e73a0812 100644
--- a/drivers/block/scsi_ioctl.c
+++ b/drivers/block/scsi_ioctl.c
@@ -231,17 +231,11 @@ static int sg_io(struct file *file, request_queue_t *q,
         if (verify_command(file, cmd))
                 return -EPERM;
 
-        /*
-         * we'll do that later
-         */
-        if (hdr->iovec_count)
-                return -EOPNOTSUPP;
-
         if (hdr->dxfer_len > (q->max_sectors << 9))
                 return -EIO;
 
         reading = writing = 0;
-        if (hdr->dxfer_len) {
+        if (hdr->dxfer_len)
                 switch (hdr->dxfer_direction) {
                 default:
                         return -EINVAL;
@@ -261,11 +255,29 @@ static int sg_io(struct file *file, request_queue_t *q,
         if (!rq)
                 return -ENOMEM;
 
-        if (reading || writing) {
-                ret = blk_rq_map_user(q, rq, hdr->dxferp, hdr->dxfer_len);
-                if (ret)
+        if (hdr->iovec_count) {
+                const int size = sizeof(struct sg_iovec) * hdr->iovec_count;
+                struct sg_iovec *iov;
+
+                iov = kmalloc(size, GFP_KERNEL);
+                if (!iov) {
+                        ret = -ENOMEM;
                         goto out;
-        }
+                }
+
+                if (copy_from_user(iov, hdr->dxferp, size)) {
+                        kfree(iov);
+                        ret = -EFAULT;
+                        goto out;
+                }
+
+                ret = blk_rq_map_user_iov(q, rq, iov, hdr->iovec_count);
+                kfree(iov);
+        } else if (hdr->dxfer_len)
+                ret = blk_rq_map_user(q, rq, hdr->dxferp, hdr->dxfer_len);
+
+        if (ret)
+                goto out;
 
         /*
          * fill in request structure