[RFC] Add user scatter gather I/O to SG_IO

James Bottomley
2005-06-10T23:59:43Z

This should be the last in the series of patches implementing
scsi_wait_req and scsi_do_req in the block layer. It adds
scatter/gather I/O from the user as a new feature of SG_IO. It also
exports the API for this which can now be used by the sg driver.

The patch is lightly tested, but appears to work fine.

James

diff --git a/drivers/block/ll_rw_blk.c b/drivers/block/ll_rw_blk.c
--- a/drivers/block/ll_rw_blk.c
+++ b/drivers/block/ll_rw_blk.c
@@ -2152,6 +2152,61 @@ struct request *blk_rq_map_user(request_
EXPORT_SYMBOL(blk_rq_map_user);

/**
+ * blk_rq_map_user - map user data to a request, for REQ_BLOCK_PC usage
+ * @q: request queue where request should be inserted
+ * @rw: READ or WRITE data
+ * @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.
+ */
+struct request *blk_rq_map_user_iov(request_queue_t *q, int rw,
+ struct sg_iovec *iov, int iov_count)
+{
+ struct request *rq;
+ struct bio *bio;
+
+ if (!iov || iov_count <= 0)
+ return ERR_PTR(-EINVAL);
+
+ rq = blk_get_request(q, rw, __GFP_WAIT);
+ if (!rq)
+ return ERR_PTR(-ENOMEM);
+
+ /* 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, rw == READ);
+
+ if (!IS_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 rq;
+ }
+
+ /*
+ * bio is the err-ptr
+ */
+ blk_put_request(rq);
+ return (struct request *) bio;
+}
+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
@@ -2231,6 +2286,21 @@ struct request *blk_rq_map_kern(request_

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
@@ -2245,13 +2315,10 @@ EXPORT_SYMBOL(blk_rq_map_kern);
int blk_execute_rq(request_queue_t *q, struct gendisk *bd_disk,
struct request *rq, int at_head)
{
- int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
DECLARE_COMPLETION(wait);
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
@@ -2264,11 +2331,8 @@ int blk_execute_rq(request_queue_t *q, s
rq->sense_len = 0;
}

- rq->flags |= REQ_NOMERGE;
rq->waiting = &wait;
- rq->end_io = blk_end_sync_rq;
- elv_add_request(q, rq, where, 1);
- generic_unplug_device(q);
+ blk_execute_rq_nowait(q, bd_disk, rq, at_head, 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
--- a/drivers/block/scsi_ioctl.c
+++ b/drivers/block/scsi_ioctl.c
@@ -231,9 +231,6 @@ static int sg_io(struct file *file, requ
if (verify_command(file, cmd))
return -EPERM;

- /*
- * we'll do that later
- */
if (hdr->iovec_count)
return -EOPNOTSUPP;

@@ -241,7 +238,7 @@ static int sg_io(struct file *file, requ
return -EIO;

reading = writing = 0;
- if (hdr->dxfer_len) {
+ if (hdr->dxfer_len)
switch (hdr->dxfer_direction) {
default:
return -EINVAL;
@@ -256,14 +253,29 @@ static int sg_io(struct file *file, requ
break;
}

+ if (hdr->iovec_count) {
+ const int size = sizeof(struct sg_iovec) * hdr->iovec_count;
+ struct sg_iovec *iov = kmalloc(size, GFP_KERNEL);
+ if (!iov)
+ return -ENOMEM;
+
+ if (copy_from_user(iov, hdr->dxferp, size)) {
+ kfree(iov);
+ return -EFAULT;
+ }
+ rq = blk_rq_map_user_iov(q, writing ? WRITE : READ, iov,
+ hdr->iovec_count);
+ kfree(iov);
+ } else if (hdr->dxfer_len) {
rq = blk_rq_map_user(q, writing ? WRITE : READ, hdr->dxferp,
hdr->dxfer_len);

- if (IS_ERR(rq))
- return PTR_ERR(rq);
} else
rq = blk_get_request(q, READ, __GFP_WAIT);

+ if (IS_ERR(rq))
+ return PTR_ERR(rq);
+
/*
* fill in request structure
*/
diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -1230,6 +1230,9 @@ static void scsi_eh_offline_sdevs(struct
scmd->device->channel,
scmd->device->id,
scmd->device->lun);
+ /* try to reset the bus and the card to a sane state */
+ scsi_try_bus_reset(scmd);
+ scsi_try_host_reset(scmd);
scsi_device_set_state(scmd->device, SDEV_OFFLINE);
if (scsi_eh_eflags_chk(scmd, SCSI_EH_CANCEL_CMD)) {
/*
diff --git a/fs/bio.c b/fs/bio.c
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -25,6 +25,7 @@
#include <linux/module.h>
#include <linux/mempool.h>
#include <linux/workqueue.h>
+#include <scsi/sg.h> /* for struct sg_iovec */

#define BIO_POOL_SIZE 256

@@ -549,22 +550,34 @@ out_bmd:
return ERR_PTR(ret);
}

-static struct bio *__bio_map_user(request_queue_t *q, struct block_device *bdev,
- unsigned long uaddr, unsigned int len,
- int write_to_vm)
+static struct bio *__bio_map_user_iov(request_queue_t *q,
+ struct block_device *bdev,
+ struct sg_iovec *iov, int iov_count,
+ int write_to_vm)
{
- unsigned long end = (uaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
- unsigned long start = uaddr >> PAGE_SHIFT;
- const int nr_pages = end - start;
- int ret, offset, i;
+ int i, j;
+ int nr_pages = 0;
struct page **pages;
struct bio *bio;
+ int cur_page = 0;
+ int ret, offset;

- /*
- * transfer and buffer must be aligned to at least hardsector
- * size for now, in the future we can relax this restriction
- */
- if ((uaddr & queue_dma_alignment(q)) || (len & queue_dma_alignment(q)))
+ for (i = 0; i < iov_count; i++) {
+ unsigned long uaddr = (unsigned long)iov[i].iov_base;
+ unsigned long len = iov[i].iov_len;
+ unsigned long end = (uaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ unsigned long start = uaddr >> PAGE_SHIFT;
+
+ nr_pages += end - start;
+ /*
+ * transfer and buffer must be aligned to at least hardsector
+ * size for now, in the future we can relax this restriction
+ */
+ if ((uaddr & queue_dma_alignment(q)) || (len & queue_dma_alignment(q)))
+ return ERR_PTR(-EINVAL);
+ }
+
+ if (!nr_pages)
return ERR_PTR(-EINVAL);

bio = bio_alloc(GFP_KERNEL, nr_pages);
@@ -576,42 +589,54 @@ static struct bio *__bio_map_user(reques
if (!pages)
goto out;

- down_read(&current->mm->mmap_sem);
- ret = get_user_pages(current, current->mm, uaddr, nr_pages,
- write_to_vm, 0, pages, NULL);
- up_read(&current->mm->mmap_sem);
+ memset(pages, 0, nr_pages * sizeof(struct page *));

- if (ret < nr_pages)
- goto out;
-
- bio->bi_bdev = bdev;
+ for (i = 0; i < iov_count; i++) {
+ unsigned long uaddr = (unsigned long)iov[i].iov_base;
+ unsigned long len = iov[i].iov_len;
+ unsigned long end = (uaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ unsigned long start = uaddr >> PAGE_SHIFT;
+ const int local_nr_pages = end - start;
+ const int page_limit = cur_page + local_nr_pages;
+
+ down_read(&current->mm->mmap_sem);
+ ret = get_user_pages(current, current->mm, uaddr,
+ local_nr_pages,
+ write_to_vm, 0, &pages[cur_page], NULL);
+ up_read(&current->mm->mmap_sem);
+
+ if (ret < local_nr_pages)
+ goto out_unmap;
+
+
+ offset = uaddr & ~PAGE_MASK;
+ for (j = cur_page; j < page_limit; j++) {
+ unsigned int bytes = PAGE_SIZE - offset;
+
+ if (len <= 0)
+ break;
+
+ if (bytes > len)
+ bytes = len;
+
+ /*
+ * sorry...
+ */
+ if (__bio_add_page(q, bio, pages[j], bytes, offset) < bytes)
+ break;

- offset = uaddr & ~PAGE_MASK;
- for (i = 0; i < nr_pages; i++) {
- unsigned int bytes = PAGE_SIZE - offset;
-
- if (len <= 0)
- break;
-
- if (bytes > len)
- bytes = len;
+ len -= bytes;
+ offset = 0;
+ }

+ cur_page = j;
/*
- * sorry...
+ * release the pages we didn't map into the bio, if any
*/
- if (__bio_add_page(q, bio, pages[i], bytes, offset) < bytes)
- break;
-
- len -= bytes;
- offset = 0;
+ while (j < page_limit)
+ page_cache_release(pages[j++]);
}

- /*
- * release the pages we didn't map into the bio, if any
- */
- while (i < nr_pages)
- page_cache_release(pages[i++]);
-
kfree(pages);

/*
@@ -620,9 +645,17 @@ static struct bio *__bio_map_user(reques
if (!write_to_vm)
bio->bi_rw |= (1 << BIO_RW);

+ bio->bi_bdev = bdev;
bio->bi_flags |= (1 << BIO_USER_MAPPED);
return bio;
-out:
+
+ out_unmap:
+ for (i = 0; i < nr_pages; i++) {
+ if(!pages[i])
+ break;
+ page_cache_release(pages[i]);
+ }
+ out:
kfree(pages);
bio_put(bio);
return ERR_PTR(ret);
@@ -642,9 +675,33 @@ out:
struct bio *bio_map_user(request_queue_t *q, struct block_device *bdev,
unsigned long uaddr, unsigned int len, int write_to_vm)
{
+ struct sg_iovec iov;
+
+ iov.iov_base = (__user void *)uaddr;
+ iov.iov_len = len;
+
+ return bio_map_user_iov(q, bdev, &iov, 1, write_to_vm);
+}
+
+/**
+ * bio_map_user_iov - map user sg_iovec table into bio
+ * @q: the request_queue_t for the bio
+ * @bdev: destination block device
+ * @iov: the iovec.
+ * @iov_count: number of elements in the iovec
+ * @write_to_vm: bool indicating writing to pages or not
+ *
+ * Map the user space address into a bio suitable for io to a block
+ * device. Returns an error pointer in case of error.
+ */
+struct bio *bio_map_user_iov(request_queue_t *q, struct block_device *bdev,
+ struct sg_iovec *iov, int iov_count,
+ int write_to_vm)
+{
struct bio *bio;
+ int len = 0, i;

- bio = __bio_map_user(q, bdev, uaddr, len, write_to_vm);
+ bio = __bio_map_user_iov(q, bdev, iov, iov_count, write_to_vm);

if (IS_ERR(bio))
return bio;
@@ -657,6 +714,9 @@ struct bio *bio_map_user(request_queue_t
*/
bio_get(bio);

+ for (i = 0; i < iov_count; i++)
+ len += iov[i].iov_len;
+
if (bio->bi_size == len)
return bio;

diff --git a/include/linux/bio.h b/include/linux/bio.h
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -281,6 +281,10 @@ extern int bio_add_page(struct bio *, st
extern int bio_get_nr_vecs(struct block_device *);
extern struct bio *bio_map_user(struct request_queue *, struct block_device *,
unsigned long, unsigned int, int);
+struct sg_iovec;
+extern struct bio *bio_map_user_iov(struct request_queue *,
+ struct block_device *,
+ struct sg_iovec *, int, int);
extern void bio_unmap_user(struct bio *);
extern struct bio *bio_map_kern(struct request_queue *, void *, unsigned int,
unsigned int);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -559,6 +559,8 @@ extern void __blk_stop_queue(request_que
extern void blk_run_queue(request_queue_t *);
extern void blk_queue_activity_fn(request_queue_t *, activity_fn *, void *);
extern struct request *blk_rq_map_user(request_queue_t *, int, void __user *, unsigned int);
+struct sg_iovec;
+extern struct request *blk_rq_map_user_iov(request_queue_t *, int, struct sg_iovec *, int);
extern int blk_rq_unmap_user(struct request *, struct bio *, unsigned int);
extern struct request *blk_rq_map_kern(request_queue_t *, int, void *,
unsigned int, unsigned int);