----- Original Message ----- > Eric Blake <ebl...@redhat.com> writes: > > > On 11/20/2015 09:23 AM, Marc-André Lureau wrote: > >> Hi > >> > >> ----- Original Message ----- > >>> Everybody's favourite device model has "size" property. It's declared > >>> as *string* > >>> > >>> DEFINE_PROP_STRING("size", IVShmemState, sizearg), > >>> > >>> > >>> * In QMP, the size must be given as JSON string instead of JSON number, > >>> and size suffixes are accepted. Example: "size": "512k" instead of > >>> "size": 524288. > >>> > >>> Right now, this violation of QMP rules is tolerable (barely), because > >>> device_add breaks some of these rules already. However, one goal of > >>> the current work on QAPI is to support a QMP command to plug devices > >>> that doesn't break QMP rules, and then this violation will stand out. > >>> > >>> Therefore, I want it fixed now, before ivshmem gets used in anger. > > > > Was ivshmem even usable in 2.4? I'd argue that if we are going to > > change it, changing it for 2.5 is the ideal time. > > Technically, we already have a compatibility break: > > $ qemu-system-x86_64 -nodefaults -S -display none -chardev > socket,path=/work/armbru/images/ivshmem-socket,id=ivshmem-chr -device > ivshmem,size=4,chardev=ivshmem-chr,shm=foo > > In 2.3.0, this ignores shm with warning "do not specify both 'chardev' > and 'shm' with ivshmem". > > In current upstream, it's rejected.
That's a regression, either we should: - keep accepting it - or keep rejection and remove the "WARNING:" Imho in this case, it was an undefined behaviour, warned, so it's fine to reject it now. > I suspect we'd find more if we cared to look. > > Of course, the only thing that *really* matters is *actual* usage in > anger: something of value that breaks. > > Hash ivshmem been used in anger? If yes, how? > > >>> A straight fix of size isn't fully backwards compatible: suffixes no > >>> longer work in QMP, and you need to use an 'M' suffix to get Mebibytes > >>> on command line and HMP. > >> > >> I don't know the rules to break properties in qemu, but I would > >> prefer to avoid it if possible. > > > > It's possible to use an alternate to accept both a string and an > > integer. But in general, QMP _wants_ to use byte-count integers without > > suffix (the convenience of '512k' is only for the command line and HMP), > > so letting QMP expose a string of "512k" instead of an integer 524288 > > feels wrong. > > Indeed. > > >>> If that's unacceptable, we'll have to provide a new, fixed property, > >>> and deprecate size. > >> > >> Sounds a better alternative to me. > > > > I'd rather fix the interface rather than catering to ugliness, > > particularly since 2.5 already fixes so much else that was ugly about > > ivshmem. > > > > Markus, did you have a patch to propose? > > Working on one. >