Re: [Qemu-devel] [PATCH] raw-posix.c: remove raw device access for cdrom

[Laurent Vivier <lvivier@redhat.com>]

On 02/07/2015 16:20, Paolo Bonzini wrote:
> 
> 
> On 02/07/2015 16:18, Laurent Vivier wrote:
>>>> I'm okay with doing the simple thing, but it needs a comment for non-BSDers.
>> So, what we have to do, in our case, for MacOS X cdrom, is something like:
>>
>> ... GetBSDPath ...
>> ...
>>     if (flags & BDRV_O_NOCACHE) {
>>         strcat(bsdPath, "r");
>>     }
>> ...
>>
>> ?
> 
> Well, what to do with Mac OS X CD-ROM is another story...  Raw access
> "seems not do work well" according to John, so we may have a comment
> there explaining why we're not adding the "r".

I think it doesn't work well because they need to be aligned, and
NOCACHE implies that (with BDRV_O_NOCACHE code will be self explicit :) )

raw_open_common()

    if ((bs->open_flags & BDRV_O_NOCACHE) != 0) {
        s->needs_alignment = true;
    }

and needs_alignment allows to probe alignment (raw_probe_alignment())

> A FIXME comment saying "we should probe for alignment here" would be
> placed where you check S_ISCHR and set need_alignment to true.

It is another case,

in the previous case (MacOS cdrom), user provides "-cdrom /dev/cdrom"
and QEMU extracts /dev/rdiskX (or now /dev/diskX) from the system DB.

In the FreeBSD case, user provides /dev/diskX or /dev/rdiskX, and QEMU
must know if it needs alignment or not. I don't think we need more
comment here.

Laurent