[Qemu-devel] [PATCH 24/23] block migration: Skip zero-sized disks

[Jan Kiszka]

Pierre Riteau wrote:
> On 30 nov. 2009, at 19:50, Pierre Riteau wrote:
> 
>> I'm currently testing these patches. Here are a few issues I noticed, before 
>> I forget about them.
>>
>> - "migrate -d -b tcp:dest:port" works, but "migrate -b -d tcp:dest:port" 
>> doesn't, although "help migrate" doesn't really specify ordering as 
>> important. But anyway I think Liran is working on a new version of the 
>> command.
>> - We use bdrv_aio_readv() to read blocks from the disk. This function 
>> increments rd_bytes and rd_ops, which are reported by "info blockstats". I 
>> don't think this read operations should appear in VM activity, especially if 
>> this interface is used by libvirt to report VM stats (and draw graphs in 
>> virt-manager, etc.). Same for write stats.
>> - We may need to call bdrv_reset_dirty() _before_ sending the data, to be 
>> sure the block is not rewritten in the meantime (maybe it's an issue only 
>> with kvm?)
>> - I seem to remember that disk images with 0 size are now possible. I'm 
>> afraid we will hit a divide by zero in this case: "progress = 
>> completed_sector_sum * 100 / block_mig_state.total_sector_sum;"
>>
>> Apart from that, it works quite fine. Still a few things to cleanup (e.g. 
>> unused constants) but much better than before.
>> However, I haven't tested the incremental transfer support at all yet. It's 
>> on my todo list.
> 
> BTW, of these four issues, only the last one is related to Jan changes. The 
> others were there before.
> This is for saying that I strongly agree with the patch series.
> 

That should catch it (yet untested, though).

Jan

----->

block migration: Skip zero-sized disks

No need to migrate emptiness (risking divide by zero later on).

Signed-off-by: Jan Kiszka <address@hidden>
---

 block-migration.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/block-migration.c b/block-migration.c
index a5735b7..98f36a4 100644
--- a/block-migration.c
+++ b/block-migration.c
@@ -222,6 +222,7 @@ static void init_blk_migration(Monitor *mon, QEMUFile *f)
 {
     BlkMigDevState *bmds;
     BlockDriverState *bs;
+    int64_t sectors;
 
     block_mig_state.submitted = 0;
     block_mig_state.read_done = 0;
@@ -231,14 +232,19 @@ static void init_blk_migration(Monitor *mon, QEMUFile *f)
 
     for (bs = bdrv_first; bs != NULL; bs = bs->next) {
         if (bs->type == BDRV_TYPE_HD) {
+            sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
+            if (sectors == 0) {
+                continue;
+            }
+
             bmds = qemu_mallocz(sizeof(BlkMigDevState));
             bmds->bs = bs;
             bmds->bulk_completed = 0;
-            bmds->total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
+            bmds->total_sectors = sectors;
             bmds->completed_sectors = 0;
             bmds->shared_base = block_mig_state.shared_base;
 
-            block_mig_state.total_sector_sum += bmds->total_sectors;
+            block_mig_state.total_sector_sum += sectors;
 
             if (bmds->shared_base) {
                 monitor_printf(mon, "Start migration for %s with shared base "

signature.asc
Description: OpenPGP digital signature