[Qemu-devel] [PATCHv2 04/11] iscsi: add bdrv_co_write_zeroes

[Peter Lieven <pl@kamp.de>]

write zeroes is emulated by unmap if the target supports unmapping
an unmapped blocks read as zero. this emulation is only done if the
device was opened with BDRV_O_UNMAP and the request can be handled
within a single request. a failback to writev is performed otherwise.

Signed-off-by: Peter Lieven <pl@kamp.de>
---
 block/iscsi.c |   44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/block/iscsi.c b/block/iscsi.c
index d31ee95..92e66a6 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -928,6 +928,49 @@ fail:
     return 0;
 }
 
+static int
+coroutine_fn iscsi_co_write_zeroes(BlockDriverState *bs, int64_t sector_num,
+                                   int nb_sectors)
+{
+    IscsiLun *iscsilun = bs->opaque;
+    struct IscsiTask iTask;
+    struct unmap_list list[1];
+
+    if (!iscsilun->lbprz || !iscsilun->lbpu || !(bs->open_flags & BDRV_O_UNMAP) ||
+        nb_sectors * BDRV_SECTOR_SIZE / iscsilun->block_size > iscsilun->max_unmap) {
+        /* fall back to writev */
+        return -ENOTSUP;
+    }
+
+    iscsi_co_init_iscsitask(iscsilun, &iTask);
+
+    list[0].lba = sector_qemu2lun(sector_num, iscsilun);
+    list[0].num = nb_sectors * BDRV_SECTOR_SIZE / iscsilun->block_size;
+
+retry:
+    if (iscsi_unmap_task(iscsilun->iscsi, iscsilun->lun, 0, 0, &list[0], 1,
+                         iscsi_co_generic_cb, &iTask) == NULL) {
+        return -EIO;
+    }
+
+    while (!iTask.complete) {
+        iscsi_set_events(iscsilun);
+        qemu_coroutine_yield();
+    }
+
+    if (iTask.do_retry) {
+        goto retry;
+    }
+
+    if (iTask.status != SCSI_STATUS_GOOD) {
+        return -EIO;
+    }
+
+    scsi_free_scsi_task(iTask.task);
+
+    return 0;
+}
+
 static int parse_chap(struct iscsi_context *iscsi, const char *target)
 {
     QemuOptsList *list;
@@ -1469,6 +1512,7 @@ static BlockDriver bdrv_iscsi = {
     .bdrv_truncate   = iscsi_truncate,
 
     .bdrv_co_is_allocated = iscsi_co_is_allocated,
+    .bdrv_co_write_zeroes = iscsi_co_write_zeroes,
 
     .bdrv_aio_readv  = iscsi_aio_readv,
     .bdrv_aio_writev = iscsi_aio_writev,
-- 
1.7.9.5