Hi Cédric, On 6/17/24 14:34, Cédric Le Goater wrote: > Hello Eric, > > On 6/17/24 1:31 PM, Eric Auger wrote: >> Hi Cédric, >> >> On 6/17/24 08:33, Cédric Le Goater wrote: >>> Since vfio_devices_dma_logging_start() takes an 'Error **' argument, >>> best practices suggest to return a bool. See the api/error.h Rules >>> section. It will simplify potential changes coming after. >> >> >> As I already mentionned the Rules section does not say that, as far as I >> understand: >> It is allowed to either return a bool, a pointer-value, an integer, >> along with an error handle: >> >> " >> * • bool-valued functions return true on success / false on failure, >> * • pointer-valued functions return non-null / null pointer, and >> * • integer-valued functions return non-negative / negative. >> " >> >> Personally I don't like much returning a bool as I think it rather >> complexifies the code and to me that kind of change is error prone. > > Returning an int could be misleading too, since there are multiple ways > it could be interpreted. You can find in QEMU routines returning -1 for > error which is later used as an errno :/ yes no good! > > The error framework in QEMU provides a way to to save and return any > kind of errors, using the error_seg_*() routines. I tend to prefer > the basic approach: return fail or pass and use the Error parameter > for details. > > Now, the problem, as always, is doing the conversion in all the > code. This is probably why people, with a kernel background, find > it confusing. > > >> >> >>> >>> vfio_container_set_dirty_page_tracking() could be modified in the same >>> way but the errno value can be saved in the migration stream when >>> called from vfio_listener_log_global_stop(). >>> Signed-off-by: Cédric Le Goater <c...@redhat.com> >>> Reviewed-by: Zhenzhong Duan <zhenzhong.d...@intel.com> >>> --- >>> hw/vfio/common.c | 14 +++++++------- >>> 1 file changed, 7 insertions(+), 7 deletions(-) >>> >>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c >>> index >>> 9e4c0cc95ff90209d3e8184035af0806a2bf890b..d48cd9b9361a92d184e423ffc60aabaff40fb487 >>> 100644 >>> --- a/hw/vfio/common.c >>> +++ b/hw/vfio/common.c >>> @@ -1020,7 +1020,7 @@ static void >>> vfio_device_feature_dma_logging_start_destroy( >>> g_free(feature); >>> } >>> -static int vfio_devices_dma_logging_start(VFIOContainerBase >>> *bcontainer, >>> +static bool vfio_devices_dma_logging_start(VFIOContainerBase >>> *bcontainer, >>> Error **errp) >>> { >>> struct vfio_device_feature *feature; >>> @@ -1033,7 +1033,7 @@ static int >>> vfio_devices_dma_logging_start(VFIOContainerBase *bcontainer, >>> &ranges); >>> if (!feature) { >>> error_setg_errno(errp, errno, "Failed to prepare DMA >>> logging"); >>> - return -errno; >>> + return false; >>> } >>> QLIST_FOREACH(vbasedev, &bcontainer->device_list, >>> container_next) { >>> @@ -1058,7 +1058,7 @@ out: >>> vfio_device_feature_dma_logging_start_destroy(feature); >>> - return ret; >>> + return ret == 0; >>> } >>> static bool vfio_listener_log_global_start(MemoryListener >>> *listener, >>> @@ -1067,18 +1067,18 @@ static bool >>> vfio_listener_log_global_start(MemoryListener *listener, >>> ERRP_GUARD(); >>> VFIOContainerBase *bcontainer = container_of(listener, >>> VFIOContainerBase, >>> listener); >>> - int ret; >>> + bool ret; >>> if (vfio_devices_all_device_dirty_tracking(bcontainer)) { >>> ret = vfio_devices_dma_logging_start(bcontainer, errp); >>> } else { >>> - ret = vfio_container_set_dirty_page_tracking(bcontainer, >>> true, errp); >>> + ret = vfio_container_set_dirty_page_tracking(bcontainer, >>> true, errp) == 0; >> >> why vfio_container_set_dirty_page_tracking(bcontainer, true, errp) >> doesn't return a bool then? > > The errno value can be saved in the migration stream when called from > vfio_listener_log_global_stop(). So this would require changes in the > migration subsystem, like we did for vfio_listener_log_global_start().
OK so although I am not a big fan of that kind of change and once highlighted this is not mandated by the error.h doc, please feel free to add my Reviewed-by: Eric Auger <eric.au...@redhat.com> Thanks Eric > > Thanks, > > C. > > > > > >> >> Eric >> >>> } >>> - if (ret) { >>> + if (!ret) { >>> error_prepend(errp, "vfio: Could not start dirty page >>> tracking - "); >>> } >>> - return !ret; >>> + return ret; >>> } >>> static void vfio_listener_log_global_stop(MemoryListener *listener) >> >