Re: raw disks no longer work in latest kvm (kvm-88 was fine)

[Antoine Martin <antoine@nagafix.co.uk>]

[snip]
>>>> The other interesting thing is that it's using pread - which means
>>>> it's a too old kernel to use preadv and thus a not very well tested
>>>> codepath with current qemu.
>> Too old?, I am confused: both host and guest kernels are 2.6.33!
>> I built KVM against the 2.6.30 headers though.
>
> You need to build qemu against the 2.6.33 headers ('make 
> headers-install').  But after we fix this, please.
OK.
I'm signing off for today, but I will test whatever patches/suggestions 
you send my way.
>
>>>
>>> It may also be that glibc is emulating preadv, incorrectly.
>> Not sure how to do that.
>>>
>>> Antoine, can you check this?  ltrace may help,
>> This the only part that looked slightly relevant:
>> [pid 26883] __xstat64(1, "./vm/media_fs", 0x7fff92e40500) = 0
>> [pid 26883] malloc(48)                           = 0x2a38d60
>> [pid 26883] memset(0x2a38d60, '\000', 48)        = 0x2a38d60
>> [pid 26883] open64("./vm/media_fs", 540674, 00)  = 12
>> [pid 26883] posix_memalign(0x7fff92e40560, 512, 16384, -1, 48) = 0
>> [pid 26883] lseek64(12, 0, 2, 0x7f404f2f3e60, 4) = 0x133c4820600
>
>
> Where's pread/preadv?  Did you use -f?
Yes I did.
ltrace -f bash ./vm/start.sh >& trace.log
>>> or run 'strings libc.so | grep pread'.
>>>
>> strings /lib/libc.so.6 | grep pread
>> preadv
>> preadv64
>> pread
>> __pread64_chk
>> __pread64
>> __pread_chk
>>
>
> So it does seem glibc emulates preadv.
>
> Perhaps https://bugzilla.redhat.com/show_bug.cgi?id=563103 ?
This a gentoo box... but yes, this does look similar doesn't it?

Antoine