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

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

1 files changed, 105 insertions, 45 deletions

diff --git a/fs/bio.c b/fs/bio.c
index c0d9140e470c..24e4045788e2 100644
--- 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(request_queue_t *q, struct block_device *bdev,
         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);
-
-        if (ret < nr_pages)
-                goto out;
-
-        bio->bi_bdev = bdev;
-
-        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;
+        memset(pages, 0, nr_pages * sizeof(struct page *));
+
+        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;
+
+                        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(request_queue_t *q, struct block_device *bdev,
         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 *q, struct block_device *bdev,
          */
         bio_get(bio);
 
+        for (i = 0; i < iov_count; i++)
+                len += iov[i].iov_len;
+
         if (bio->bi_size == len)
                 return bio;