[Qemu-devel] [PATCHv3 0/3] introduce max_transfer_length

[Qemu-devel] [PATCHv3 0/3] introduce max_transfer_length

[Peter Lieven]

This series adds the basics for introducing a maximum transfer length
to the block layer. Its main purpose is currently avoiding that
a multiwrite_merge exceeds the max_xfer_len of an attached iSCSI LUN.
This is a required bug fix.

Splitting up requests according to the max_transfer_length will follow
in a later series.

v2->v3: remove Patch 2 completely [Paolo]
v1->v2: do not throw errors but generate trace events in Patch 2 [Paolo]

Peter Lieven (3):
  BlockLimits: introduce max_transfer_length
  block/iscsi: set max_transfer_length
  block: avoid creating oversized writes in multiwrite_merge

 block.c                   |    9 +++++++++
 block/iscsi.c             |   12 ++++++++++--
 include/block/block_int.h |    3 +++
 3 files changed, 22 insertions(+), 2 deletions(-)

-- 
1.7.9.5

[Qemu-devel] [PATCHv3 1/3] BlockLimits: introduce max_transfer_length

[Peter Lieven]

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
---
 block.c                   |    4 ++++
 include/block/block_int.h |    3 +++
 2 files changed, 7 insertions(+)

diff --git a/block.c b/block.c
index c5a251c..26806e0 100644
--- a/block.c
+++ b/block.c
@@ -541,6 +541,7 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
             return;
         }
         bs->bl.opt_transfer_length = bs->file->bl.opt_transfer_length;
+        bs->bl.max_transfer_length = bs->file->bl.max_transfer_length;
         bs->bl.opt_mem_alignment = bs->file->bl.opt_mem_alignment;
     } else {
         bs->bl.opt_mem_alignment = 512;
@@ -555,6 +556,9 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
         bs->bl.opt_transfer_length =
             MAX(bs->bl.opt_transfer_length,
                 bs->backing_hd->bl.opt_transfer_length);
+        bs->bl.max_transfer_length =
+            MIN(bs->bl.max_transfer_length,
+                bs->backing_hd->bl.max_transfer_length);
         bs->bl.opt_mem_alignment =
             MAX(bs->bl.opt_mem_alignment,
                 bs->backing_hd->bl.opt_mem_alignment);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 8d86a6c..b13a10a 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -289,6 +289,9 @@ typedef struct BlockLimits {
     /* optimal transfer length in sectors */
     int opt_transfer_length;
 
+    /* maximal transfer length in sectors */
+    int max_transfer_length;
+
     /* memory alignment so that no bounce buffer is needed */
     size_t opt_mem_alignment;
 } BlockLimits;
-- 
1.7.9.5

[Qemu-devel] [PATCHv3 2/3] block/iscsi: set max_transfer_length

[Peter Lieven]

the limit of 0xffffff for 16 byte CDBs is intentional to
avoid overflows on 32-bit architectures.

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
---
 block/iscsi.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/block/iscsi.c b/block/iscsi.c
index 5c72ffe..16fe8bc 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -1441,10 +1441,18 @@ static void iscsi_close(BlockDriverState *bs)
 
 static void iscsi_refresh_limits(BlockDriverState *bs, Error **errp)
 {
-    IscsiLun *iscsilun = bs->opaque;
-
     /* We don't actually refresh here, but just return data queried in
      * iscsi_open(): iscsi targets don't change their limits. */
+
+    IscsiLun *iscsilun = bs->opaque;
+    uint32_t max_xfer_len = iscsilun->use_16_for_rw ? 0xffffff : 0xffff;
+
+    if (iscsilun->bl.max_xfer_len) {
+        max_xfer_len = MIN(max_xfer_len, iscsilun->bl.max_xfer_len);
+    }
+
+    bs->bl.max_transfer_length = sector_lun2qemu(max_xfer_len, iscsilun);
+
     if (iscsilun->lbp.lbpu) {
         if (iscsilun->bl.max_unmap < 0xffffffff) {
             bs->bl.max_discard = sector_lun2qemu(iscsilun->bl.max_unmap,
-- 
1.7.9.5

[Qemu-devel] [PATCHv3 3/3] block: avoid creating oversized writes in multiwrite_merge

[Peter Lieven]

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
---
 block.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/block.c b/block.c
index 26806e0..a26e6a5 100644
--- a/block.c
+++ b/block.c
@@ -4559,6 +4559,11 @@ static int multiwrite_merge(BlockDriverState *bs, BlockRequest *reqs,
             merge = 0;
         }
 
+        if (bs->bl.max_transfer_length && reqs[outidx].nb_sectors +
+            reqs[i].nb_sectors > bs->bl.max_transfer_length) {
+            merge = 0;
+        }
+
         if (merge) {
             size_t size;
             QEMUIOVector *qiov = g_malloc0(sizeof(*qiov));
-- 
1.7.9.5