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.
> 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/
>
>
>
