Re: Blkparse weirdness with "A" (remap) action

["Alan D. Brunelle" <Alan.Brunelle@hp.com>]

Jens Axboe wrote:
> On Fri, Jul 27 2007, Paul P Komkoff Jr wrote:
>   
>> Replying to Paul P Komkoff Jr:
>>     
>>> I'm having a little problem here. I have a setup with md over some
>>> disks, and I'm running blktrace /dev/md? /dev/sd?, then doing blkparse
>>> *.blktrace.*, I'm getting this kind of stuff:
>>>
>>>  40,131071  1       67     3.043450168   420  A   W 4274944 + 8 <- (253,0) 4275328
>>>  40,131071  1       67     3.043450168   420  A   W 4274944 + 8 <- (253,0) 4275328
>>>       
>> Replying to my own message.
>> I assume this is because we have this in kernel:
>>
>> /*
>>  * The remap event
>>  */
>> struct blk_io_trace_remap {
>>         __be32 device;
>>         u32 __pad;
>>         __be64 sector;
>> };
>>
>> but this in blktrace:
>>
>> /*
>>  * The remap event
>>  */
>> struct blk_io_trace_remap {
>>         __u32 device;
>>         __u32 device_from;
>>         __u64 sector;
>> };
>>     
>
> I think Alan had a patch for filling in that missing device_from value,
> currently it's not used in the kernel (as you spotted). Alan?
>
>   
I have submitted these patches at least twice - once last fall, and once
again this spring - the latter time a certain someone named Axboe said
they'd be going in for sure... :-)

I'm back from holiday and will get cracking on getting an updated set of
patches out soon...

Alan
PS. Basically, there were a couple of spots in the kernel (partition
remaps & LVM2/DM remaps) that filled in the device_from fields...