[GEDI] [PATCH v2 06/17] block/io: support int64_t bytes in bdrv_aligned_pwritev()

Vladimir Sementsov-Ogievskiy vsementsov at virtuozzo.com
Thu Apr 30 05:25:22 UTC 2020

30.04.2020 1:04, Eric Blake wrote:
> On 4/27/20 3:23 AM, Vladimir Sementsov-Ogievskiy wrote:
>> We are generally moving to int64_t for both offset and bytes parameters
>> on all io paths. Prepare bdrv_aligned_pwritev() now (and convert the
>> dependencies: bdrv_co_write_req_prepare() and
>> bdrv_co_write_req_finish() to signed type bytes)
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov at virtuozzo.com>
>> ---
>>   block/io.c | 12 +++++++-----
>>   1 file changed, 7 insertions(+), 5 deletions(-)
>> diff --git a/block/io.c b/block/io.c
>> index c8c30e3699..fe19e09034 100644
>> --- a/block/io.c
>> +++ b/block/io.c
>> @@ -1854,7 +1854,7 @@ fail:
>>   }
>>   static inline int coroutine_fn
>> -bdrv_co_write_req_prepare(BdrvChild *child, int64_t offset, uint64_t bytes,
>> +bdrv_co_write_req_prepare(BdrvChild *child, int64_t offset, int64_t bytes,
>>                             BdrvTrackedRequest *req, int flags)
>>   {
> No change in size.  First, check usage within function:
>      int64_t end_sector = DIV_ROUND_UP(offset + bytes, BDRV_SECTOR_SIZE);
> Changes computation from uint64_t to int64_t.  This causes a borderline bug on images between INT64_MAX-511 and INT64_MAX (nbdkit can produce such images over NBD, although they are atypical on disk), where DIV_ROUND_UP() would give the right answer as uint64_t but a negative answer with int64_t.  As those images are not sector-aligned, maybe we don't need to care?
> all other uses appear to be within asserts related to offset+bytes being positive, so that's what we should check for.
> Callers:
> bdrv_aligned_pwritev() - changed in this patch to 'int64_t', analyzed below [1]
> bdrv_co_pdiscard() - already passes 'int64_t', also checks for offset+bytes overflow - safe
> bdrv_co_copy_range_internal() - 'uint64_t', but already analyzed for 3/17 how it was capped < 2M - safe
> bdrv_co_truncate() - already passes 'int64_t', passes new_bytes computed by subtracting from a positive 'int64_t offset' - safe
> [1] except I hit the end of my work day, so my analysis will have to continue tomorrow...

Thanks for reviewing!

I'm very sorry, I just need to say once again: the series should be rebased on "[PATCH for-5.0? 0/9] block/io: safer inc/dec in_flight sections", as it is already mostly reviewed by Stefan. Seems, that your analysis will be still valid after it, although patches will change. I'll do it now to see, can I keep your r-b's.

Best regards,

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