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Subject[PATCH 11/17] bio: add sgl source support to bci and implement bio_memcpy_sgl_sgl()
Date
Impact: add new features to internal functions to prepare for future changes

Expand bci such that it supports sgl as source and implement
bio_memcpy_sgl_sgl() which can copy data between two sgls. These will
be used to implement blk_rq_copy/map_kern_iov().

Signed-off-by: Tejun Heo <tj@kernel.org>
---
fs/bio.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++++++++++------
1 files changed, 74 insertions(+), 8 deletions(-)
diff --git a/fs/bio.c b/fs/bio.c
index 1ca8b16..04bc5c2 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -758,8 +758,10 @@ err:
struct bio_copy_info {
struct scatterlist *copy_sgl; /* one sg per page */
struct iovec *src_iov; /* source iovec from userland */
+ struct scatterlist *src_sgl; /* source sgl */
int copy_nents; /* #entries in copy_sgl */
int src_count; /* #entries in src_iov */
+ int src_nents; /* #entries in src_sgl */
size_t len; /* total length in bytes */
int is_our_pages; /* do we own copied pages? */
};
@@ -776,6 +778,7 @@ static void bci_destroy(struct bio_copy_info *bci)
bio_sgl_free_pages(bci->copy_sgl, bci->copy_nents);
kfree(bci->copy_sgl);
kfree(bci->src_iov);
+ kfree(bci->src_sgl);
kfree(bci);
}

@@ -783,6 +786,8 @@ static void bci_destroy(struct bio_copy_info *bci)
* bci_create - create a bci
* @src_iov: source iovec
* @src_count: number of entries in @src_iov
+ * @src_sgl: source sgl
+ * @src_nents: number of entries in @src_sgl
* @gfp: gfp for data structure allocations
* @page_gfp: gfp for page allocations
* @md: optional preallocated page pool
@@ -795,28 +800,47 @@ static void bci_destroy(struct bio_copy_info *bci)
* Pointer to the new bci on success, NULL on failure.
*/
static struct bio_copy_info *bci_create(struct iovec *src_iov, int src_count,
- gfp_t gfp, gfp_t page_gfp,
- struct rq_map_data *md)
+ struct scatterlist *src_sgl, int src_nents,
+ gfp_t gfp, gfp_t page_gfp,
+ struct rq_map_data *md)
{
struct bio_copy_info *bci;
+ struct scatterlist *sg;
+ int i;
+
+ BUG_ON(!src_iov == !src_sgl);

bci = kzalloc(sizeof(*bci), gfp);
if (!bci)
return NULL;

bci->src_count = src_count;
- bci->len = iov_length(src_iov, src_count);
+ bci->src_nents = src_nents;
bci->is_our_pages = md == NULL;

+ if (src_iov)
+ bci->len = iov_length(src_iov, src_count);
+ else
+ for_each_sg(src_sgl, sg, src_nents, i)
+ bci->len += sg->length;
+
bci->copy_sgl = bio_alloc_sgl_with_pages(bci->len, gfp, page_gfp, md,
&bci->copy_nents);
if (!bci->copy_sgl)
goto err;

- bci->src_iov = kmalloc(sizeof(src_iov[0]) * src_count, gfp);
- if (!bci->src_iov)
- goto err;
- memcpy(bci->src_iov, src_iov, sizeof(src_iov[0]) * src_count);
+ if (src_iov) {
+ bci->src_iov = kmalloc(sizeof(src_iov[0]) * src_count, gfp);
+ if (!bci->src_iov)
+ goto err;
+ memcpy(bci->src_iov, src_iov, sizeof(src_iov[0]) * src_count);
+ } else {
+ bci->src_sgl = kmalloc(sizeof(src_sgl[0]) * src_nents, gfp);
+ if (!bci->src_sgl)
+ goto err;
+ for_each_sg(src_sgl, sg, src_nents, i)
+ bci->src_sgl[i] = *sg;
+ }

return bci;

@@ -925,6 +949,48 @@ static void bio_init_from_sgl(struct bio *bio, struct request_queue *q,
}

/**
+ * bio_memcpy_sgl_sgl - copy data betweel two sgls
+ * @dsgl: destination sgl
+ * @dnents: number of entries in @dsgl
+ * @ssgl: source sgl
+ * @snents: number of entries in @ssgl
+ *
+ * Copy data from @ssgl to @dsgl. The areas should be of the
+ * same size.
+ */
+static void bio_memcpy_sgl_sgl(struct scatterlist *dsgl, int dnents,
+ struct scatterlist *ssgl, int snents)
+{
+ struct sg_mapping_iter si, di;
+
+ /*
+ * si will be nested inside di, use atomic mapping for it to
+ * avoid (mostly theoretical) possibility of deadlock.
+ */
+ sg_miter_start(&di, dsgl, dnents, 0);
+ sg_miter_start(&si, ssgl, snents, SG_MITER_ATOMIC);
+
+ while (sg_miter_next(&di)) {
+ void *daddr = di.addr;
+ size_t dlen = di.length;
+
+ while (dlen && sg_miter_next(&si)) {
+ size_t copy = min(dlen, si.length);
+
+ memcpy(daddr, si.addr, copy);
+
+ daddr += copy;
+ dlen -= copy;
+ si.consumed = copy;
+ }
+ WARN_ON_ONCE(dlen); /* ssgl too short */
+ sg_miter_stop(&si); /* advancing di might sleep, stop si */
+ }
+ WARN_ON_ONCE(sg_miter_next(&si)); /* dsgl too short */
+ sg_miter_stop(&di);
+}
+
+/**
* bio_create_from_sgl - create bio from sgl
* @q: request_queue new bio belongs to
* @sgl: sgl describing the data area
@@ -993,7 +1059,7 @@ struct bio *bio_copy_user_iov(struct request_queue *q, struct rq_map_data *md,
struct bio *bio;
int ret;

- bci = bci_create(iov, count, gfp, q->bounce_gfp | gfp, md);
+ bci = bci_create(iov, count, NULL, 0, gfp, q->bounce_gfp | gfp, md);
if (!bci)
return ERR_PTR(-ENOMEM);

--
1.6.0.2


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