2011/1/21 Pierre Riteau <pierre.rit...@irisa.fr>:
> Le 20 janv. 2011 à 17:18, Yoshiaki Tamura <tamura.yoshi...@lab.ntt.co.jp> a
> écrit :
>
>> 2011/1/20 Pierre Riteau <pierre.rit...@irisa.fr>:
>>> On 20 janv. 2011, at 03:06, Yoshiaki Tamura wrote:
>>>
>>>> 2011/1/19 Pierre Riteau <pierre.rit...@irisa.fr>:
>>>>> b02bea3a85cc939f09aa674a3f1e4f36d418c007 added a check on the return
>>>>> value of bdrv_write and aborts migration when it fails. However, if the
>>>>> size of the block device to migrate is not a multiple of BLOCK_SIZE
>>>>> (currently 1 MB), the last bdrv_write will fail with -EIO.
>>>>>
>>>>> Fixed by calling bdrv_write with the correct size of the last block.
>>>>> ---
>>>>> block-migration.c | 16 +++++++++++++++-
>>>>> 1 files changed, 15 insertions(+), 1 deletions(-)
>>>>>
>>>>> diff --git a/block-migration.c b/block-migration.c
>>>>> index 1475325..eeb9c62 100644
>>>>> --- a/block-migration.c
>>>>> +++ b/block-migration.c
>>>>> @@ -635,6 +635,8 @@ static int block_load(QEMUFile *f, void *opaque, int
>>>>> version_id)
>>>>> int64_t addr;
>>>>> BlockDriverState *bs;
>>>>> uint8_t *buf;
>>>>> + int64_t total_sectors;
>>>>> + int nr_sectors;
>>>>>
>>>>> do {
>>>>> addr = qemu_get_be64(f);
>>>>> @@ -656,10 +658,22 @@ static int block_load(QEMUFile *f, void *opaque,
>>>>> int version_id)
>>>>> return -EINVAL;
>>>>> }
>>>>>
>>>>> + total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
>>>>> + if (total_sectors <= 0) {
>>>>> + fprintf(stderr, "Error getting length of block device
>>>>> %s\n", device_name);
>>>>> + return -EINVAL;
>>>>> + }
>>>>> +
>>>>> + if (total_sectors - addr < BDRV_SECTORS_PER_DIRTY_CHUNK) {
>>>>> + nr_sectors = total_sectors - addr;
>>>>> + } else {
>>>>> + nr_sectors = BDRV_SECTORS_PER_DIRTY_CHUNK;
>>>>> + }
>>>>> +
>>>>> buf = qemu_malloc(BLOCK_SIZE);
>>>>>
>>>>> qemu_get_buffer(f, buf, BLOCK_SIZE);
>>>>> - ret = bdrv_write(bs, addr, buf,
>>>>> BDRV_SECTORS_PER_DIRTY_CHUNK);
>>>>> + ret = bdrv_write(bs, addr, buf, nr_sectors);
>>>>>
>>>>> qemu_free(buf);
>>>>> if (ret < 0) {
>>>>> --
>>>>> 1.7.3.5
>>>>>
>>>>>
>>>>>
>>>>
>>>> Hi Pierre,
>>>>
>>>> I don't think the fix above is correct. If you have a file which
>>>> isn't aliened with BLOCK_SIZE, you won't get an error with the
>>>> patch. However, the receiver doesn't know how much sectors which
>>>> the sender wants to be written, so the guest may fail after
>>>> migration because some data may not be written. IIUC, although
>>>> changing bytestream should be prevented as much as possible, we
>>>> should save/load total_sectors to check appropriate file is
>>>> allocated on the receiver side.
>>>
>>> Isn't the guest supposed to be started using a file with the correct size?
>>
>> I personally don't like that; It's insisting too much to the user.
>> Can't we expand the image on the fly? We can just abort if expanding
>> failed anyway.
>
> At first I thought your expansion idea was best, but now I think there are
> valid scenarios where it fails.
>
> Imagine both sides are not using a file but a disk partition as storage. If
> the partition size is not rounded to 1 MB, the last write will fail with the
> current code, and there is no way we can expand the partition.
>
Right. But in case of partition doesn't the check in the patch below
return error? Does bdrv_getlength return the size correctly?
total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
if (total_sectors <= 0) {
fprintf(stderr, "Error getting length of block device %s\n", device_name);
return -EINVAL;
}
Yoshi
>>> But I guess changing the protocol would be best as it would avoid headaches
>>> to people who mistakenly created a file that is too small.
>>
>> We should think carefully before changing the protocol.
>>
>> Kevin?
>>
>>>
>>>> BTW, you should use error_report instead of fprintf(stderr, ...).
>>>
>>> I didn't know that, I followed what was used in this file. Thank you.
>>>
>>> --
>>> Pierre Riteau -- PhD student, Myriads team, IRISA, Rennes, France
>>> http://perso.univ-rennes1.fr/pierre.riteau/
>>>
>>>
>>>
>
>
