[Qemu-devel] Re: [PATCH 03/11] raw-posix: Don't "try harder" for BDRV_TYPE_CDROM

[Markus Armbruster]

Kevin Wolf <address@hidden> writes:

> Am 30.06.2010 13:55, schrieb Markus Armbruster:
>> raw_pread_aligned() retries up to two times if the block device backs
>> a virtual CD-ROM.  This makes no sense.  Whether retrying reads can
>> correct read errors may depend on what we're reading, not on how the
>> result gets used.
>> 
>> Also clean up gratuitous use of goto.
>> 
>> This reverts what's left of commit 8c05dbf9.
>> 
>> Signed-off-by: Markus Armbruster <address@hidden>
>
> Are you sure that this won't cause a regression? I mean if there is a
> patch specifically adding this behaviour, there probably was a problem
> that made someone touch the code in the first place.
>
> Arguably checking for the type hint is nonsense, however I think the
> case for which this was written is passing through a real CD-ROM to a VM
> - in which case the condition would be true anyway.
>
> So instead of removing the code, the fix to achieve what was probably
> intended is to check for bs->drv == &bdrv_host_cdrom.

I can do that.  But does it make sense?  How can retrying failed reads
help?  Isn't the OS in a much better position to retry?

Keeping the retry code feels like voodoo-programming to me: I have no
idea how waving around this dead chicken could help, but we've always
done it, so keep waving ;)