Re: [Qemu-devel] [PATCH v2] usb-mtp: Add fallback definition of NAME_MAX

[Kamil Rytarowski <n54@gmx.com>]

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On 04.09.2017 19:50, Peter Maydell wrote:
> On 4 September 2017 at 18:25, Kamil Rytarowski <n54@gmx.com> wrote:
>> This fixes build on SmartOS (Joyent).
>>
>> Patch cherry-picked from pkgsrc by jperkin (Joyent).
>>
>> Signed-off-by: Kamil Rytarowski <n54@gmx.com>
>> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>> ---
>>  include/qemu/osdep.h | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
>> index 6855b94bbf..5d3860f80e 100644
>> --- a/include/qemu/osdep.h
>> +++ b/include/qemu/osdep.h
>> @@ -306,6 +306,11 @@ void qemu_anon_ram_free(void *ptr, size_t size);
>>  #endif
>>  #endif
>>
>> +/* Required by SmartOS (SunOS) */
>> +#ifndef NAME_MAX
>> +#define NAME_MAX 255
>> +#endif
> 
> So in hw/usb/dev-mtp.c we're using NAME_MAX in
>     char buf[sizeof(struct inotify_event) + NAME_MAX + 1];
> 
> because the Linux implementation of inotify documents in inotify(7)
> that this is guaranteed to be sufficient to read at least one event:
>   http://man7.org/linux/man-pages/man7/inotify.7.html
> Looking at the SmartOS manpage
>   https://smartos.org/man/5/inotify
> there doesn't seem to be any equivalent language.
> 
> What is the SmartOS requirement on the buffer size to be
> guaranteed to read at least one complete event ?
> Defining NAME_MAX to 255 seems like it shuts up the compiler
> error but does it give us the correct behaviour?
> 
According to my understanding SmartOS has the same logic. It tries to
read at least one element, and NAME_MAX guarantees that it will be
available.

https://github.com/joyent/illumos-joyent/blob/master/usr/src/uts/common/io/inotify.c#L1193

I've gathered some overall details about the patches.

1. The inotify linux-compat interface is only SmartOS specific, it
hasn't been upstreamed so far to other Illumos distributions.

2. Upstream Illumos implemented NAME_MAX
https://github.com/illumos/illumos-gate/commit/9c0752ac0dc05794d2f8a8b4521d55e2b3f63247

It's not available in SmartOS.

3. Proprietary Solaris is out of scope of this work.

Looking at their userland we can assume no qemu support:

https://github.com/oracle/solaris-userland

https://github.com/oracle/solaris-userland/commit/9c78c7b45a5d3dbd64afb455d278d2ca277e2b95#diff-94df904ebca88ee0ff038eaedb063ad6R61

++        if platform.system() == 'SunOS':
++            # No QEMU support on Solaris now.
++            qemu_img = False

We can stop pretending to support it now.

4. SmartOS forked qemu for its hypervisor part and uses qemu-kvm with
the Linux kvm interface (yes, there is Linux kernel kvm port to SmartOS)
- upstreaming the hypervisor's fork is out of scope.

https://github.com/joyent/illumos-kvm-cmd

5. SmartOS ships with virtual machine guests, they host pkgsrc and qemu
from pkgsrc.

6. Jonathan mentioned that preparing a SmartOS tutorial and image will
be tricky, as SmartOS is a hypervisor. I will focus on upstreaming
SmartOS-guest support for qemu, where there is pkgsrc. There is an
option to prepare another Illumos distribution tutorial and testbot,
hopefully it will be fully compatible with SmartOS patches.

> thanks
> -- PMM
> 



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