[Qemu-devel] [PULL 10/12] block/iscsi: fix rounding in iscsi_allocationmap_set

[Paolo Bonzini <pbonzini@redhat.com>]

From: Peter Lieven <pl@kamp.de>

when setting clusters as alloacted the boundaries have
to be expanded. As Paolo pointed out the calculation of
the number of clusters is wrong:

Suppose cluster_sectors is 2, sector_num = 1, nb_sectors = 6:

In the "mark allocated" case, you want to set 0..8, i.e.
cluster_num=0, nb_clusters=4.

   0--.--2--.--4--.--6--.--8
   <--|_________________|-->  (<--> = expanded)

Instead you are setting nb_clusters=3, so that 6..8 is not marked.

   0--.--2--.--4--.--6--.--8
   <--|______________|!!!     (! = wrong)

Cc: qemu-stable@nongnu.org
Reported-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Peter Lieven <pl@kamp.de>
Message-Id: <1468831940-15556-2-git-send-email-pl@kamp.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block/iscsi.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/block/iscsi.c b/block/iscsi.c
index cf1e9e7..22330e1 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -432,12 +432,14 @@ static unsigned long *iscsi_allocationmap_init(IscsiLun *iscsilun)
 static void iscsi_allocationmap_set(IscsiLun *iscsilun, int64_t sector_num,
                                     int nb_sectors)
 {
+    int64_t cluster_num, nb_clusters;
     if (iscsilun->allocationmap == NULL) {
         return;
     }
-    bitmap_set(iscsilun->allocationmap,
-               sector_num / iscsilun->cluster_sectors,
-               DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
+    cluster_num = sector_num / iscsilun->cluster_sectors;
+    nb_clusters = DIV_ROUND_UP(sector_num + nb_sectors,
+                               iscsilun->cluster_sectors) - cluster_num;
+    bitmap_set(iscsilun->allocationmap, cluster_num, nb_clusters);
 }
 
 static void iscsi_allocationmap_clear(IscsiLun *iscsilun, int64_t sector_num,
-- 
2.7.4