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From: "adhemerval.zanella at linaro dot org"
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Subject: [Bug build/26338] io/tst-copy_file_range fails on RHEL 7.8 hosts
Date: Wed, 05 Aug 2020 14:20:19 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D26338

--- Comment #6 from Adhemerval Zanella <adhemerval.zanella at linaro dot or=
g> ---
(In reply to Florian Weimer from comment #5)
> (In reply to Adhemerval Zanella from comment #4)
> > So I don't think ENOSYS as RHEL 7.8 is doing is the correct way to adve=
rtise
> > the syscall does not work depending of the underlying filesystem (at le=
ast
> > it seems not what upstream is doing).
>=20
> It would break cp from coreutils, which only recognizes ENOSYS, EINVAL,
> EBADF, EXDEV as soft errors.
>=20
> The EOPNOTSUPPs you listed should not leak into userspace because they
> trigger generic splice-based copy_file_range fallback, and splice apparen=
tly
> fails with EINVAL in case of missing file system support.
>=20
> It's true that ENOSYS breaks programs that cache the availability of the
> system call and assume that the error is parameter-independent. EINVAL mi=
ght
> have been the better choice for that reason.

It seems that in very simplified mode the call sequence is:

  copy_file_range
  \_ vfs_copy_file_range
     \_ remap_file_range
     \_ do_copy_file_range
        \_ file_out->f_op->copy_file_range
        \_ generic_copy_file_range


However on do_copy_file_range the generic_copy_file_range is not actually
called is the filesystem one fails. The vfs_copy_file_range does WARN_ON_ON=
CE
on EOPNOTSUPP, but afaiu it indeed might leak to userspace (although it mig=
ht
characterize as a bug).

But I agree that EINVAL is indeed a better return code and it is what
generic_copy_file_range does for such cases.

--=20
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