On 4/9/14, 3:48 PM, Mark Tinguely wrote:
> On 04/09/14 14:15, Eric Sandeen wrote:
>> xfs_io's pread & pwrite claim to support a random IO mode
>> where it will do random IOs between offset & offset+len.
>>
>> However, offset was ignored, and we did the IOs between 0
>> and len instead.
>>
>> Clang caught this by pointing out that the calculated/normalized
>> "offset" variable was never read.
>>
>> (NB: If the range is larger than RAND_MAX, these functions don't
>> work, but that's always been true, so I'll leave it for another
>> day...)
>>
>> Signed-off-by: Eric Sandeen<sandeen@xxxxxxxxxx>
>> ---
>>
>> I haven't tested this w/ xfstests but I don't see anyone who calls
>> pread/pwrite with "-R" (and it's not documented in the manpage!)
>>
>> diff --git a/io/pread.c b/io/pread.c
>> index a42baed..465c22b 100644
>> --- a/io/pread.c
>> +++ b/io/pread.c
>> @@ -246,7 +246,7 @@ read_random(
>
> offset can be the end of file offset. Do we care that the read (/write)
> could start or end past the end of file?
It now behaves the same as a normal forward read does if you tell it
to go past EOF:
xfs_io> truncate 1g
xfs_io> pread 1g 1m
read 0/1048576 bytes at offset 1073741824
0.000000 bytes, 0 ops; 0.0000 sec (0.000000 bytes/sec and 0.0000 ops/sec)
xfs_io> pread -R 1g 1m
read 0/1048576 bytes at offset 1073741824
0.000000 bytes, 0 ops; 0.0000 sec (0.000000 bytes/sec and 0.0000 ops/sec)
so I think it's ok?
>>
>> *total = 0;
>> while (count > 0) {
>> - off = ((random() % range) / buffersize) * buffersize;
>> + off = ((offset + (random() % range)) / buffersize) * buffersize;
>> bytes = do_pread(fd, off, buffersize, buffersize);
>> if (bytes == 0)
>> break;
>
> Looks like this was introduced in:
> commit 8fb2237e65555ff540e8b6108ffccfffefe239ac
> Author: Nathan Scott <nathans@xxxxxxx>
> Date: Fri Nov 11 14:25:18 2005 +0000
>
> Provide further debugging options and tweaks for analysing the read/write paths.
> Merge of master-melb:xfs-cmds:24372a by kenmcd.
>
> ---
>
> If it was broken for 8.5 years, I think it could be removed.
Eh, could, or we could fix it. :) I suppose this means it needs a test... :/
-Eric
> --Mark.
>
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