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.
>> 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/
>>
>>
>>
