Re: kcmp implementation for mesa

instead of messing with code like this it's probably time to implement
kcmp in the kernel

On 1/19/24, Michael Zhilin <mizhka@gmail.com> wrote:
> Hi Ivan,
>
> Looks good. Could you please put patch on reviews.freebsd.org?
>
> Thx,
> Michael
>
> On Fri, 19 Jan 2024, 14:11 Rozhuk Ivan, <rozhuk.im@gmail.com> wrote:
>
>> Hi!
>>
>>
>> graphics/mesa-* uses SYS_kcmp [1] to compare two fds:
>>
>> int
>> os_same_file_description(int fd1, int fd2)
>> {
>>    pid_t pid = getpid();
>>
>>    /* Same file descriptor trivially implies same file description */
>>    if (fd1 == fd2)
>>       return 0;
>>
>>    return syscall(SYS_kcmp, pid, pid, KCMP_FILE, fd1, fd2);
>> }
>>
>> FreeBSD does not implemet this and we got in terminal:
>> "amdgpu: os_same_file_description couldn't determine if two DRM fds
>> reference the same file description."
>>
>>
>> Mesa say:
>> /* DRM file descriptors, file descriptions and buffer sharing.
>>  *
>>  * amdgpu_device_initialize first argument is a file descriptor (fd)
>>  * representing a specific GPU.
>>  * If a fd is duplicated using os_dupfd_cloexec,
>>  * the file description will remain the same (os_same_file_description
>> will
>>  * return 0).
>>  * But if the same device is re-opened, the fd and the file description
>> will
>>  * be different.
>>  *
>>  * amdgpu_screen_winsys's fd tracks the file description which was
>>  * given to amdgpu_winsys_create. This is the fd used by the application
>>  * using the driver and may be used in other ioctl (eg: drmModeAddFB)
>>  *
>>  * amdgpu_winsys's fd is the file description used to initialize the
>>  * device handle in libdrm_amdgpu.
>>  *
>>  * The 2 fds can be different, even in systems with a single GPU, eg: if
>>  * radv is initialized before radeonsi.
>>  *
>>  * This fd tracking is useful for buffer sharing because KMS/GEM handles
>> are
>>  * specific to a DRM file description, i.e. the same handle value may
>> refer
>>  * to different underlying BOs in different DRM file descriptions.
>>  * As an example, if an app wants to use drmModeAddFB it'll need a KMS
>> handle
>>  * valid for its fd (== amdgpu_screen_winsys::fd).
>>  * If both fds are identical, there's nothing to do:
>> bo->u.real.kms_handle
>>  * can be used directly (see amdgpu_bo_get_handle).
>>  * If they're different, the BO has to be exported from the device fd as
>>  * a dma-buf, then imported from the app fd as a KMS handle.
>>  */
>>
>>
>>
>> I do few checks with dup() and os_dupfd_cloexec() and code show that fd
>> equal.
>>
>> Does this implementation will do that mesa expects?
>>
>>
>> #include <sys/user.h>
>> #include <fcntl.h>
>>
>> int
>> os_same_file_description(int fd1, int fd2) {
>>         struct kinfo_file kif1, kif2;
>>
>>         /* Same file descriptor trivially implies same file description
>> */
>>         if (fd1 == fd2)
>>                 return (0);
>>
>>         kif1.kf_structsize = sizeof(kif1);
>>         kif2.kf_structsize = sizeof(kif2);
>>         if (-1 == fcntl(fd1, F_KINFO, &kif1) ||
>>             -1 == fcntl(fd2, F_KINFO, &kif2))
>>                 return (-1);
>>
>>         if (kif1.kf_type != kif2.kf_type ||
>>             0 != memcmp(&kif1.kf_path, &kif2.kf_path,
>> sizeof(kif1.kf_path)))
>>                 return (3);
>>
>>         switch (kif1.kf_type) {
>>         case KF_TYPE_VNODE:
>>                 if (0 == memcmp(&kif1.kf_un.kf_file, &kif2.kf_un.kf_file,
>>                     sizeof(kif1.kf_un.kf_file)))
>>                         return (0);
>>                 return (3);
>>         case KF_TYPE_SOCKET:
>>                 if (0 == memcmp(&kif1.kf_un.kf_sock, &kif2.kf_un.kf_sock,
>>                     sizeof(kif1.kf_un.kf_sock)))
>>                         return (0);
>>                 return (3);
>>         case KF_TYPE_PIPE:
>>                 if (0 == memcmp(&kif1.kf_un.kf_pipe, &kif2.kf_un.kf_pipe,
>>                     sizeof(kif1.kf_un.kf_pipe)))
>>                         return (0);
>>                 return (3);
>>         //case KF_TYPE_FIFO:
>>         case KF_TYPE_KQUEUE:
>>                 if (0 == memcmp(&kif1.kf_un.kf_kqueue,
>> &kif2.kf_un.kf_kqueue,
>>                     sizeof(kif1.kf_un.kf_kqueue)))
>>                         return (0);
>>                 return (3);
>>         //case KF_TYPE_MQUEUE:
>>         //case KF_TYPE_SHM:
>>         case KF_TYPE_SEM:
>>                 if (0 == memcmp(&kif1.kf_un.kf_sem, &kif2.kf_un.kf_sem,
>>                     sizeof(kif1.kf_un.kf_sem)))
>>                         return (0);
>>                 return (3);
>>         case KF_TYPE_PTS:
>>                 if (0 == memcmp(&kif1.kf_un.kf_pts, &kif2.kf_un.kf_pts,
>>                     sizeof(kif1.kf_un.kf_pts)))
>>                         return (0);
>>                 return (3);
>>         case KF_TYPE_PROCDESC:
>>                 if (0 == memcmp(&kif1.kf_un.kf_proc, &kif2.kf_un.kf_proc,
>>                     sizeof(kif1.kf_un.kf_proc)))
>>                         return (0);
>>                 return (3);
>>         //case KF_TYPE_DEV:
>>         case KF_TYPE_EVENTFD:
>>                 if (0 == memcmp(&kif1.kf_un.kf_eventfd,
>> &kif2.kf_un.kf_eventfd,
>>                     sizeof(kif1.kf_un.kf_eventfd)))
>>                         return (0);
>>                 return (3);
>>         case KF_TYPE_TIMERFD:
>>                 if (0 == memcmp(&kif1.kf_un.kf_timerfd,
>> &kif2.kf_un.kf_timerfd,
>>                     sizeof(kif1.kf_un.kf_timerfd)))
>>                         return (0);
>>                 return (3);
>>         }
>>         /* Otherwise we can't tell */
>>         return (-1);
>> }
>>
>>
>> Refs:
>> 1. https://man7.org/linux/man-pages/man2/kcmp.2.html
>>
>>
>>
>


-- 
Mateusz Guzik <mjguzik gmail.com>