lkml.org 
[lkml]   [2023]   [Oct]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRE: [PATCH v4 13/15] uapi: hyperv: Add mshv driver headers defining hypervisor ABIs
    Date
    > From: Greg KH <gregkh@linuxfoundation.org>
    > Sent: Tuesday, October 3, 2023 11:10 PM
    > [...]
    > On Tue, Oct 03, 2023 at 04:37:01PM -0700, Nuno Das Neves wrote:
    > > On 9/30/2023 11:19 PM, Greg KH wrote:
    > > > On Sat, Sep 30, 2023 at 10:01:58PM +0000, Wei Liu wrote:
    > > > > On Sat, Sep 30, 2023 at 08:09:19AM +0200, Greg KH wrote:
    > > > > > On Fri, Sep 29, 2023 at 11:01:39AM -0700, Nuno Das Neves wrote:
    > > > > > > +/* Define connection identifier type. */
    > > > > > > +union hv_connection_id {
    > > > > > > + __u32 asu32;
    > > > > > > + struct {
    > > > > > > + __u32 id:24;
    > > > > > > + __u32 reserved:8;
    > > > > > > + } __packed u;

    IMO the "__packed" is unnecessary.

    > > > > > bitfields will not work properly in uapi .h files, please never do that.
    > > > >
    > > > > Can you clarify a bit more why it wouldn't work? Endianess? Alignment?
    > > >
    > > > Yes to both.
    > > >
    > > > Did you all read the documentation for how to write a kernel api? If
    > > > not, please do so. I think it mentions bitfields, but it not, it really
    > > > should as of course, this will not work properly with different endian
    > > > systems or many compilers.
    > >
    > > Yes, in
    > https://docs.k/
    > ernel.org%2Fdriver-
    > api%2Fioctl.html&data=05%7C01%7Cdecui%40microsoft.com%7Ce404769e0f
    > 85493f0aa108dbc4a08a27%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C
    > 0%7C638319966071263290%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLj
    > AwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%
    > 7C%7C&sdata=RiLNA5DRviWBQK6XXhxC4m77raSDBb%2F0BB6BDpFPUJY%3D
    > &reserved=0 it says that it is
    > > "better to avoid" bitfields.
    > >
    > > Unfortunately bitfields are used in the definition of the hypervisor
    > > ABI. We import these definitions directly from the hypervisor code.
    >
    > So why do you feel you have to use this specific format for your
    > user/kernel api? That is not what is going to the hypervisor.

    If it's hard to avoid bitfield here, maybe we can refer to the definition of
    struct iphdr in include/uapi/linux/ip.h

    Thanks,
    Dexuan

    \
     
     \ /
      Last update: 2023-10-04 19:37    [W:6.030 / U:0.084 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site