Re: [Qemu-devel] [RFC PATCH 03/14] quorum: ignore 0-length child

[Wen Congyang]

On 02/24/2015 04:43 AM, Max Reitz wrote:
> On 2015-02-11 at 22:07, Wen Congyang wrote:
>> We connect to NBD server when starting block replication, so
>> the length is 0 before starting block replication.
>>
>> Signed-off-by: Wen Congyang <address@hidden>
>> Signed-off-by: zhanghailiang <address@hidden>
>> Signed-off-by: Gonglei <address@hidden>
>> ---
>>   block/quorum.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/block/quorum.c b/block/quorum.c
>> index 5ed1ff8..e6aff5f 100644
>> --- a/block/quorum.c
>> +++ b/block/quorum.c
>> @@ -734,6 +734,11 @@ static int64_t quorum_getlength(BlockDriverState *bs)
>>           if (value < 0) {
>>               return value;
>>           }
>> +
>> +        if (!value) {
>> +            continue;
>> +        }
>> +
>>           if (value != result) {
>>               return -EIO;
>>           }
> 
> Hm, what do you think about some specific error value returned by your 
> delayed NBD implementation? Like -ENOTCONN or something like that? Then we'd 
> be able to discern a real 0-length block device from a not-yet-connected NBD 
> server.

In my newest test, it cannot return -ENOTCONN, otherwise bdrv_open() will fail 
when we open the child.
Here is the backtrace:
(gdb) bt
#0  bdrv_open_common (bs=0x5555563b2230, file=0x0, options=0x5555563b55a0, 
flags=57410, drv=0x555555e90c00, errp=0x7fffffffd460) at block.c:1070
#1  0x000055555595ea72 in bdrv_open (pbs=0x7fffffffd5f8, filename=0x0, 
reference=0x0, options=0x5555563b55a0, flags=57410, drv=0x555555e90c00, 
errp=0x7fffffffd5e0) at block.c:1677
#2  0x000055555595e3a9 in bdrv_open_image (pbs=0x7fffffffd5f8, filename=0x0, 
options=0x5555563a6730, bdref_key=0x555555a86b4c "file", flags=57410, 
allow_none=true, errp=0x7fffffffd5e0) at block.c:1481
#3  0x000055555595e9ae in bdrv_open (pbs=0x555556388008, filename=0x0, 
reference=0x0, options=0x5555563a6730, flags=8258, drv=0x555555e8b800, 
errp=0x7fffffffd6b8) at block.c:1655
#4  0x00005555559b0058 in quorum_open (bs=0x55555639bd90, 
options=0x55555639f100, flags=8258, errp=0x7fffffffd758) at block/quorum.c:1000
#5  0x000055555595d0b8 in bdrv_open_common (bs=0x55555639bd90, file=0x0, 
options=0x55555639f100, flags=8258, drv=0x555555e8e5c0, errp=0x7fffffffd840) at 
block.c:1045
#6  0x000055555595ea72 in bdrv_open (pbs=0x55555639bd50, filename=0x0, 
reference=0x0, options=0x55555639f100, flags=8258, drv=0x555555e8e5c0, 
errp=0x7fffffffdb70) at block.c:1677
#7  0x00005555559b3bd3 in blk_new_open (name=0x55555639bc60 "virtio0", 
filename=0x0, reference=0x0, options=0x55555639a420, flags=66, 
errp=0x7fffffffdb70) at block/block-backend.c:129
#8  0x0000555555754f78 in blockdev_init (file=0x0, bs_opts=0x55555639a420, 
errp=0x7fffffffdb70) at blockdev.c:536
#9  0x0000555555755d90 in drive_new (all_opts=0x5555563777e0, 
block_default_type=IF_IDE) at blockdev.c:971
#10 0x000055555576b1f0 in drive_init_func (opts=0x5555563777e0, 
opaque=0x555556372b48) at vl.c:1104
#11 0x0000555555a1b019 in qemu_opts_foreach (list=0x555555e44060, 
func=0x55555576b1ba <drive_init_func>, opaque=0x555556372b48, 
abort_on_failure=1) at util/qemu-option.c:1059
#12 0x00005555557743dd in main (argc=25, argv=0x7fffffffe0c8, 
envp=0x7fffffffe198) at vl.c:4191

refresh_total_sectors() will fail if we return -ENOTCONN.

Thanks
Wen Congyang

> 
> Also, while you did write that one shouldn't be using the NBD client as the 
> first quorum child, I think we should try to support that case anyway. For 
> this patch, that means accepting that bdrv_getlength(s->bs[0]) may be off.
> 
> Max
> .
>