Date: Wed, 20 Sep 2023 17:39:05 -0700 From: Rick Macklem <rick.macklem@gmail.com> To: John F Carr <jfc@mit.edu> Cc: Freebsd fs <freebsd-fs@freebsd.org> Subject: Re: RFC: Should copy_file_range(2) work for shared memory objects? Message-ID: <CAM5tNy58oxf7ui6DpuLbsLAk4K7U9B28XsJQAtN=wk3o9vxeQQ@mail.gmail.com> In-Reply-To: <CABAD93F-E6B1-44A2-BD14-F3CC547EC7DA@mit.edu> References: <CAM5tNy4HxY8LK0f6baGhu=opoC3-4ODhqNyxoyPY8vdwxGs5Xg@mail.gmail.com> <CABAD93F-E6B1-44A2-BD14-F3CC547EC7DA@mit.edu>
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On Wed, Sep 20, 2023 at 4:54=E2=80=AFPM John F Carr <jfc@mit.edu> wrote:
>
> On Sep 20, 2023, at 16:47, Rick Macklem <rick.macklem@gmail.com> wrote:
> >
> > Right now (as noted by PR#273962) copy_file_range(2)
> > fails for shared memory objects because there is no
> > vnode (f_vnode =3D=3D NULL) for them and the code uses
> > vnodes (including a file system specific VOP_COPY_FILE_RANGE(9)).
> >
> > Do you think copy_file_range(2) should work for shared memory objects?
> >
> > This would require specific handling in kern_copy_file_range()
> > to work. I do not think the patch would be a lot of work, but
> > I am not familiar with the f_ops and shared memory code.
> >
> > rick
> >
>
> According to a Linux man page, some failure modes are
>
> EINVAL Either fd_in or fd_out is not a regular file.
>
> EOPNOTSUPP (since Linux 5.19) The filesystem does not support this=
operation.
>
> EXDEV (since Linux 5.19)
> The files referred to by fd_in and fd_out are not on the
> same filesystem, and the source and target filesystems are
> not of the same type, or do not support cross-filesystem copy=
.
>
> According to the FreeBSD man page
>
> The copy_file_range() system call is expected to be compatible with =
the
> Linux system call of the same name.
>
So, I guess you are advocating for sticking with "Linux compatible"?
I'm fine with that, but we'll see what others say.
Thanks for your comments, rick
ps; When I go look at the Linux man page, I often get an out-of-dat
one, so I am never sure what Linux currently does. (It is also
confusing because some distros implement copy_file_range()
in their libc instead of the kernel. I think more recent Linux kernels
do support the syscall.)
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