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Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB |
Date: |
Fri, 21 Jan 2011 13:31:10 +0100 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.15) Gecko/20101027 Fedora/3.0.10-1.fc12 Thunderbird/3.0.10 |
Am 21.01.2011 13:15, schrieb Yoshiaki Tamura:
> 2011/1/21 Pierre Riteau <address@hidden>:
>> Le 20 janv. 2011 à 17:18, Yoshiaki Tamura <address@hidden> a écrit :
>>
>>> 2011/1/20 Pierre Riteau <address@hidden>:
>>>> On 20 janv. 2011, at 03:06, Yoshiaki Tamura wrote:
>>>>
>>>>> 2011/1/19 Pierre Riteau <address@hidden>:
>>>>>> 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?
I'm pretty sure that it does. We would have problems in other places if
it didn't (e.g. we're checking if I/O requests are within the disk size).
Kevin
- [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Pierre Riteau, 2011/01/19
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Yoshiaki Tamura, 2011/01/19
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Pierre Riteau, 2011/01/20
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Yoshiaki Tamura, 2011/01/21
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB,
Kevin Wolf <=
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Yoshiaki Tamura, 2011/01/21
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Pierre Riteau, 2011/01/21
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Yoshiaki Tamura, 2011/01/21
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Kevin Wolf, 2011/01/21
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Yoshiaki Tamura, 2011/01/21
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Pierre Riteau, 2011/01/21
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Yoshiaki Tamura, 2011/01/21
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Pierre Riteau, 2011/01/21
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Yoshiaki Tamura, 2011/01/21
- Re: [Qemu-devel] [PATCH] Fix block migration when the device size is not a multiple of 1 MB, Pierre Riteau, 2011/01/21