[PATCH v4 1/1] linux/termios: test the kernel-side termios canonicalization

[H.J. Lu]

On Wed, Nov 19, 2025 at 2:21 AM H. Peter Anvin <hpa@zytor.com> wrote:
>
> Verify that the kernel side of the termios interface gets the various
> speed fields set according to our current canonicalization policy.
>
> [ v2.1: fix formatting - Adhemerval Netto ]
> [ v4: fix typo in patch description - Dan Horák ]
>
> Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> (v2.1)
> ---
>  sysdeps/unix/sysv/linux/tst-termios-linux.c | 61 ++++++++++++++++++++-
>  1 file changed, 58 insertions(+), 3 deletions(-)
>
> diff --git a/sysdeps/unix/sysv/linux/tst-termios-linux.c b/sysdeps/unix/sysv/linux/tst-termios-linux.c
> index e4b0c8bcd6ed..80ba9e885363 100644
> --- a/sysdeps/unix/sysv/linux/tst-termios-linux.c
> +++ b/sysdeps/unix/sysv/linux/tst-termios-linux.c
> @@ -38,6 +38,8 @@
>  #include <support/test-driver.h>
>  #include <support/tty.h>
>
> +#include <k_termios.h>        /* Definitions for the raw ioctl interface */
> +
>  /* Evaluate an expression and make sure errno did not get set; return
>     the value of the expression */
>  #define CHECKERR(expr)                         \
> @@ -226,13 +228,66 @@ static void check_speeds_cf (const struct termios *tio_p,
>                CHECKERR (cfgetibaud (tio_p)), 'i');
>  }
>
> -/* Use this after tc[gs]etattr () */
> +/* Access the raw kernel interface and verify that the result is
> +   canonicalized properly; this should be run after tcsetattr (). */
> +static void
> +check_speeds_kernel (int fd, speed_t ospeed, speed_t ispeed)
> +{
> +  struct termios2 k_termios;
> +  tcflag_t expect_cbaud = speed_to_cbaud (ospeed);
> +  tcflag_t expect_cibaud;
> +
> +  if (!ispeed)
> +    ispeed = ospeed;
> +
> +  /* If ospeed == ispeed, tcsetattr() should set the kernel CIBAUD to 0,
> +     for compatibility with programs that use the direct ioctl interface
> +     but fail to account for CIBAUD. c_ispeed should still be correct. */
> +  if (ospeed == ispeed)
> +    expect_cibaud = 0;
> +  else
> +    expect_cibaud = speed_to_cbaud (ispeed);
> +
> +  memset (&k_termios, 0xed, sizeof k_termios); /* Fill with nonsense */
> +  CHECKZERO (ioctl(fd, TCGETS2, &k_termios));
> +
> +  tcflag_t k_cbaud  = k_termios.c_cflag & CBAUD;
> +  tcflag_t k_cibaud = (k_termios.c_cflag >> IBSHIFT) & CBAUD;
> +
> +  if (k_termios.c_ospeed != ospeed)
> +    FAIL ("opeed %u ispeed %u: kernel c_ospeed = %u, expected %u",
> +         ospeed, ispeed,
> +         k_termios.c_ospeed, ospeed);
> +
> +  if (k_cbaud != expect_cbaud)
> +    FAIL ("ospeed %u ispeed %u: kernel CBAUD = %s (%06o), expected %s (%06o)",
> +         ospeed, ispeed,
> +         cbaud_name (k_cbaud), k_cbaud,
> +         cbaud_name (expect_cbaud), expect_cbaud);
> +
> +  if (k_termios.c_ispeed != ispeed)
> +    FAIL ("ospeed %u ispeed %u: kernel c_ispeed == %u, expected %u",
> +         ospeed, ispeed,
> +         k_termios.c_ispeed, ispeed);
> +
> +  if (k_cibaud != expect_cibaud)
> +    FAIL ("ospeed %u ispeed %u: kernel CIBAUD = %s (%06o), expected %s (%06o)",
> +         ospeed, ispeed,
> +         cbaud_name (k_cibaud), k_cibaud,
> +         cbaud_name (expect_cibaud), expect_cibaud);
> +}
> +
> +/* Use this after tcsetattr () */
>  static void check_speeds_tc (int fd, speed_t ospeed, speed_t ispeed)
>  {
>    struct termios tio;
>
> +  if (!ispeed)
> +    ispeed = ospeed;
> +
>    CHECKZERO (tcgetattr (fd, &tio));
> -  check_speeds_cf (&tio, ospeed, ispeed ? ispeed : ospeed);
> +  check_speeds_cf (&tio, ospeed, ispeed);
> +  check_speeds_kernel (fd, ospeed, ispeed);
>  }
>
>  /* For search and replace convenience */
> @@ -250,7 +305,7 @@ set_speeds (int fd, speed_t ospeed, speed_t ispeed)
>    CHECKZERO (cfsetispeed (&tio, ispeed));
>    check_speeds_cf (&tio, ospeed, ispeed);
>    CHECKZERO (tcsetattr (fd, TCSANOW, &tio));
> -  check_speeds_tc (fd, ospeed, ispeed ? ispeed : ospeed);
> +  check_speeds_tc (fd, ospeed, ispeed);
>  }
>
>  /* Actual tests */
> --
> 2.51.1
>

LGTM.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

Thanks.

-- 
H.J.