[Qemu-devel] [PATCH 2/2] iscsi: add intelligent has_zero_init check

[Peter Lieven <pl@kamp.de>]

iscsi targets are not created by bdrv_create and thus we cannot
blindly assume that a target is empty. to avoid writing and allocating
blocks of zeroes we now check if all blocks of an existing target
are unallocated and return 1 for bdrv_has_zero_init if the
target is completely unalloacted and unallocated blocks read
as zeroes.

Signed-off-by: Peter Lieven <pl@kamp.de>
---
 block/iscsi.c |   25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/block/iscsi.c b/block/iscsi.c
index e6b966d..fe41d9a 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -50,6 +50,7 @@ typedef struct IscsiLun {
     int events;
     QEMUTimer *nop_timer;
     uint8_t lbpme;
+    uint8_t lbprz;
 } IscsiLun;
 
 typedef struct IscsiAIOCB {
@@ -1004,6 +1005,7 @@ static int iscsi_readcapacity_sync(IscsiLun *iscsilun)
                     iscsilun->block_size = rc16->block_length;
                     iscsilun->num_blocks = rc16->returned_lba + 1;
                     iscsilun->lbpme = rc16->lbpme;
+                    iscsilun->lbprz = rc16->lbprz;
                 }
             }
             break;
@@ -1249,7 +1251,28 @@ static int iscsi_truncate(BlockDriverState *bs, int64_t offset)
 
 static int iscsi_has_zero_init(BlockDriverState *bs)
 {
-    return 0;
+    IscsiLun *iscsilun = bs->opaque;
+    uint64_t lba;
+    int n, ret, nb_sectors;
+
+    if (iscsilun->lbprz == 0) {
+        return 0;
+    }
+
+    for (lba = 0; lba < iscsilun->num_blocks; lba += 1 << 26) {
+        nb_sectors = 1 << 26;
+        if (lba + nb_sectors > iscsilun->num_blocks) {
+            nb_sectors = iscsilun->num_blocks - lba;
+        }
+        nb_sectors *= (iscsilun->block_size / BDRV_SECTOR_SIZE);
+        n = 0;
+        ret = iscsi_co_is_allocated(bs, lba, nb_sectors, &n);
+        if (ret || n != nb_sectors) {
+            return 0;
+        }
+    }
+
+    return 1;
 }
 
 static int iscsi_create(const char *filename, QEMUOptionParameter *options)
-- 
1.7.9.5