[RFC PATCH 2/3] tcm_iscsi: support multiple sizes in the scatterlist

Paolo Bonzini
2012-09-05T15:15:38Z

The next patch will use multiple orders to satisfy the allocation
of the data buffers.

We need to support this in iscsi_map_iovec and iscsi_unmap_iovec.
The idea here is to walk each relevant page in the scatterlist
(which may not be every page in the scatterlist due to data_offset)
and kmap it. iscsi_unmap_iovec uses the same algorithm, so that
each kunmap maps the kmap that was used in iscsi_map_iovec.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
drivers/target/iscsi/iscsi_target.c | 106 ++++++++++++++++++++++++-----
drivers/target/iscsi/iscsi_target_core.h | 2 +-
2 files changed, 89 insertions(+), 19 deletions(-)

diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
index 224679e..dc4f5da 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -684,45 +684,115 @@ static int iscsit_map_iovec(
u32 data_offset,
u32 data_length)
{
- u32 i = 0;
struct scatterlist *sg;
- unsigned int page_off;
+ u32 sg_off, sg_left, cur_len;
+ u32 sg_pfn = 0;
+ u32 i = 0;

- /*
- * We know each entry in t_data_sg contains a page.
- */
- sg = &cmd->se_cmd.t_data_sg[data_offset / PAGE_SIZE];
- page_off = (data_offset % PAGE_SIZE);
+ sg = cmd->se_cmd.t_data_sg;
+ while (data_offset >= sg->length) {
+ data_offset -= sg->length;
+ sg++;
+ }

cmd->first_data_sg = sg;
- cmd->first_data_sg_off = page_off;
+ cmd->first_data_sg_off = sg->offset + data_offset;
+ cmd->kmapped_length = data_length;

+ sg_left = 0;
while (data_length) {
- u32 cur_len = min_t(u32, data_length, sg->length - page_off);
+ if (!sg_left) {
+ sg_off = sg->offset + data_offset;
+ sg_pfn = page_to_pfn(sg_page(sg));
+ sg_pfn += sg_off >> PAGE_SHIFT;
+ sg_off &= PAGE_SIZE - 1;
+
+ sg_left = min(sg->length, data_length);
+
+ /*
+ * The next scatterlist is mapped from the beginning.
+ */
+ sg++;
+ data_offset = 0;
+ }

- iov[i].iov_base = kmap(sg_page(sg)) + sg->offset + page_off;
+ /*
+ * Create an iovec for (a part of) this page.
+ */
+ cur_len = min_t(u32, PAGE_SIZE - sg_off, sg_left);
+ BUG_ON(!cur_len);
+
+ iov[i].iov_base = kmap(pfn_to_page(sg_pfn)) + sg_off;
iov[i].iov_len = cur_len;
+ i++;

data_length -= cur_len;
- page_off = 0;
- sg = sg_next(sg);
- i++;
- }
+ sg_left -= cur_len;

- cmd->kmapped_nents = i;
+ /*
+ * The next pfn is mapped from the beginning.
+ */
+ sg_pfn++;
+ sg_off = 0;
+ }

+ BUG_ON(sg_left);
return i;
}

static void iscsit_unmap_iovec(struct iscsi_cmd *cmd)
{
- u32 i;
struct scatterlist *sg;
+ u32 data_offset, data_length;
+ u32 sg_off, sg_left, cur_len;
+ u32 sg_pfn = 0;
+
+ if (!cmd->kmapped_length)
+ return;

sg = cmd->first_data_sg;
+ data_offset = cmd->first_data_sg_off - sg->offset;
+ data_length = cmd->kmapped_length;
+
+ /*
+ * This loop must mirror exactly what is done in iscsi_map_iovec.
+ */
+ sg_left = 0;
+ while (data_length) {
+ if (!sg_left) {
+ sg_off = sg->offset + data_offset;
+ sg_pfn = page_to_pfn(sg_page(sg));
+ sg_pfn += sg_off >> PAGE_SHIFT;
+ sg_off &= PAGE_SIZE - 1;
+
+ sg_left = min(sg->length, data_length);
+
+ /*
+ * The next scatterlist is mapped from the beginning.
+ */
+ sg++;
+ data_offset = 0;
+ }
+
+ /*
+ * Create an iovec for (a part of) this page.
+ */
+ cur_len = min_t(u32, PAGE_SIZE - sg_off, sg_left);
+ BUG_ON(!cur_len);
+
+ kunmap(pfn_to_page(sg_pfn));
+ data_length -= cur_len;
+ sg_left -= cur_len;
+
+ /*
+ * The next pfn is mapped from the beginning.
+ */
+ sg_pfn++;
+ sg_off = 0;
+ }

- for (i = 0; i < cmd->kmapped_nents; i++)
- kunmap(sg_page(&sg[i]));
+ BUG_ON(sg_left);
+ cmd->kmapped_length = 0;
}

static void iscsit_ack_from_expstatsn(struct iscsi_conn *conn, u32 exp_statsn)
diff --git a/drivers/target/iscsi/iscsi_target_core.h b/drivers/target/iscsi/iscsi_target_core.h
index 8a908b2..13bdaf1 100644
--- a/drivers/target/iscsi/iscsi_target_core.h
+++ b/drivers/target/iscsi/iscsi_target_core.h
@@ -472,7 +472,7 @@ struct iscsi_cmd {

struct scatterlist *first_data_sg;
u32 first_data_sg_off;
- u32 kmapped_nents;
+ u32 kmapped_length;

} ____cacheline_aligned;

--
1.7.1