Re: [edk2-devel] [edk2-libc Patch 1/1] edk2-libc/StdLib: Fix console jump to 0, 0 issue in lseek()

["Pedro Falcato" <pedro.falcato@gmail.com>]

On Thu, Aug 24, 2023 at 5:34 PM Jayaprakash, N <n.jayaprakash@intel.com> wrote:
>
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4531
>
> Python code opens console file descriptor and uses lseek()
> with position == 0 and SEEK_CUR as
> 'do nothing, check console is alive' operation.
>
> Current implementation of daConsole ignores whence argument,
> this is wrong in case lseek(0, SEEK_CUR) will send cursor to (0,0).
> This fix is not generic, but solves the particular situation.
>
> Cc: Rebecca Cran <rebecca@bsdio.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Cc: Jayaprakash N <n.jayaprakash@intel.com>
> Signed-off-by: Kloper Dimitry <dimitry.kloper@intel.com>
> ---
>  StdLib/LibC/Uefi/Devices/Console/daConsole.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/StdLib/LibC/Uefi/Devices/Console/daConsole.c b/StdLib/LibC/Uefi/Devices/Console/daConsole.c
> index 56571af..ba031d6 100644
> --- a/StdLib/LibC/Uefi/Devices/Console/daConsole.c
> +++ b/StdLib/LibC/Uefi/Devices/Console/daConsole.c
> @@ -141,8 +141,16 @@ da_ConSeek(
>      EFIerrno = RETURN_UNSUPPORTED;
>      return -1;
>    }
> -  // Everything is OK to do the final verification and "seek".
> +
>    Proto = (EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL *)Stream->Dev;
> +
> +  if(Position == 0 && whence == SEEK_CUR) {
> +    CursorPos.XYpos.Column  = (UINT32)Proto->Mode->CursorColumn;
> +    CursorPos.XYpos.Row     = (UINT32)Proto->Mode->CursorRow;
> +    return CursorPos.Offset;
> +  }
> +
> +  // Everything is OK to do the final verification and "seek".
>    CursorPos.Offset = Position;
>
>    EFIerrno = Proto->SetCursorPosition(Proto,
> --
> 2.40.0.windows.1

ttys are historically not seekable devices.

per Linux lseek(2): "On Linux, using lseek() on a terminal device
fails with the error ESPIPE"

So this function (and consequently this patch) is wrong.

-- 
Pedro


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