[PATCH 9/9] block: Add bio_get_user_pages()

Kent Overstreet
2013-11-04T23:37:08Z

This replaces some of the code that was in __bio_map_user_iov(), and
soon we're going to use this helper in the dio code.

Note that this relies on the recent change to make
generic_make_request() take arbitrary sized bios - we're not using
bio_add_page() here.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
---
fs/bio.c | 124 +++++++++++++++++++++++++++-------------------------
include/linux/bio.h | 2 +
2 files changed, 67 insertions(+), 59 deletions(-)

diff --git a/fs/bio.c b/fs/bio.c
index c60bfcb..a10b350 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -1124,17 +1124,70 @@ struct bio *bio_copy_user(struct request_queue *q, struct rq_map_data *map_data,
}
EXPORT_SYMBOL(bio_copy_user);

+/**
+ * bio_get_user_pages - pin user pages and add them to a biovec
+ * @bio: bio to add pages to
+ * @uaddr: start of user address
+ * @len: length in bytes
+ * @write_to_vm: bool indicating writing to pages or not
+ *
+ * Pins pages for up to @len bytes and appends them to @bio's bvec array. May
+ * pin only part of the requested pages - @bio need not have room for all the
+ * pages and can already have had pages added to it.
+ *
+ * Returns the number of bytes from @len added to @bio.
+ */
+ssize_t bio_get_user_pages(struct bio *bio, unsigned long uaddr,
+ unsigned long len, int write_to_vm)
+{
+ int ret;
+ unsigned nr_pages, bytes;
+ unsigned offset = offset_in_page(uaddr);
+ struct bio_vec *bv;
+ struct page **pages;
+
+ nr_pages = min_t(size_t,
+ DIV_ROUND_UP(len + offset, PAGE_SIZE),
+ bio->bi_max_vecs - bio->bi_vcnt);
+
+ bv = &bio->bi_io_vec[bio->bi_vcnt];
+ pages = (void *) bv;
+
+ ret = get_user_pages_fast(uaddr, nr_pages, write_to_vm, pages);
+ if (ret < 0)
+ return ret;
+
+ bio->bi_vcnt += ret;
+ bytes = ret * PAGE_SIZE - offset;
+
+ while (ret--) {
+ bv[ret].bv_page = pages[ret];
+ bv[ret].bv_len = PAGE_SIZE;
+ bv[ret].bv_offset = 0;
+ }
+
+ bv[0].bv_offset += offset;
+ bv[0].bv_len -= offset;
+
+ if (bytes > len) {
+ bio->bi_io_vec[bio->bi_vcnt - 1].bv_len -= bytes - len;
+ bytes = len;
+ }
+
+ bio->bi_iter.bi_size += bytes;
+
+ return bytes;
+}
+EXPORT_SYMBOL(bio_get_user_pages);
+
static struct bio *__bio_map_user_iov(struct request_queue *q,
struct block_device *bdev,
struct sg_iovec *iov, int iov_count,
int write_to_vm, gfp_t gfp_mask)
{
- int i, j;
- int nr_pages = 0;
- struct page **pages;
+ ssize_t ret;
+ int i, nr_pages = 0;
struct bio *bio;
- int cur_page = 0;
- int ret, offset;

for (i = 0; i < iov_count; i++) {
unsigned long uaddr = (unsigned long)iov[i].iov_base;
@@ -1163,57 +1216,17 @@ static struct bio *__bio_map_user_iov(struct request_queue *q,
if (!bio)
return ERR_PTR(-ENOMEM);

- ret = -ENOMEM;
- pages = kcalloc(nr_pages, sizeof(struct page *), gfp_mask);
- if (!pages)
- goto out;
-
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;
-
- ret = get_user_pages_fast(uaddr, local_nr_pages,
- write_to_vm, &pages[cur_page]);
- if (ret < local_nr_pages) {
- ret = -EFAULT;
- goto out_unmap;
- }
-
- offset = uaddr & ~PAGE_MASK;
- for (j = cur_page; j < page_limit; j++) {
- unsigned int bytes = PAGE_SIZE - offset;
+ ret = bio_get_user_pages(bio, (size_t) iov[i].iov_base,
+ iov[i].iov_len,
+ write_to_vm);
+ if (ret < 0)
+ goto out;

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

- kfree(pages);
-
/*
* set data direction, and check if mapped pages need bouncing
*/
@@ -1224,14 +1237,7 @@ static struct bio *__bio_map_user_iov(struct request_queue *q,
bio->bi_flags |= (1 << BIO_USER_MAPPED);
return bio;

- 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);
}
diff --git a/include/linux/bio.h b/include/linux/bio.h
index d0c0cc7..af4976e 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -356,6 +356,8 @@ void bio_chain(struct bio *, struct bio *);

extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
extern int bio_get_nr_vecs(struct block_device *);
+extern ssize_t bio_get_user_pages(struct bio *, unsigned long,
+ unsigned long, int);
extern struct bio *bio_map_user(struct request_queue *, struct block_device *,
unsigned long, unsigned int, int, gfp_t);
struct sg_iovec;
--
1.8.4.rc3