[PATCH] Linux: Define struct termios2 in <termios.h> under _GNU_SOURCE [BZ #10339]
Adhemerval Zanella
adhemerval.zanella at linaro.org
Thu Apr 11 06:24:17 AEST 2019
On 09/04/2019 07:47, Florian Weimer wrote:
> struct termios2 is required for setting arbitrary baud rates on serial
> ports. <sys/ioctl.h> and <linux/termios.h> have conflicting
> definitions in the existing termios definitions, which means that it
> is currently very difficult to use TCGETS2/TCSETS2 and struct termios2
> with glibc. Providing a definition within glibc resolves this problem.
>
> This does not completely address bug 10339, but it at least exposes
> the current kernel functionality in this area.
>
> Support for struct termios2 is architecture-specific in the kernel.
> Support on alpha was only added in Linux 4.20. POWER support is
> currently missing. The expectation is that the kernel will eventually
> use the generic UAPI definition for struct termios2.
I still think the better strategy, from both BZ#10339 and recent thread
discussion about the issue on libc-alpha, is rather to:
1. Start to use termios2 ioctl kabi instead of termios1. The only
missing spot is alpha pre linux 4.20.
2. Adjust sparc and mips to add c_ispeed and c_ospeed along with
compat symbols to use termios1. This will allow also some cleanup
to remove _HAVE_STRUCT_TERMIOS_C_{O,I}SPEED.
3. Use the compat symbols for alpha pre-4.20.
4. With termios Linux ABI being essentially the same for all supported
architectures (with support for c_ospeed and c_ispeed) we can move
forward to adapt the current cfgetospeed, cfgetispeed, cfsetospeed,
cfsetispeed to work with arbitrary values.
The POSIX and Linux extended BXX values will need to be handled
exceptionally. It means their integers values will be reserved and
mapped to the termios2 values. The code resulting code for cfsetospeed,
for instance, would be:
---
static inline speed_t
c_ispeed (tcflag_t c_cflag)
{
return (c_cflag >> IBSHIFT) & CBAUD;
}
/*
* The top four bits in speed_t are reserved for future use, and *currently*
* the equivalent values are the only valid baud_t values.
*/
static inline bool
invalid_speed (speed_t x)
{
return x > 0x0fffffff;
}
/* Set the output baud rate stored in *TERMIOS_P to the symbol SPEED */
int
cfsetospeed (struct termios *termios_p, speed_t speed)
{
if (invalid_speed (speed))
{
__set_errno (EINVAL);
return -1;
}
termios_p->c_ospeed = speed_kernel_from_user (speed);
if ( c_ispeed (termios_p->c_cflag) == B0 )
termios_p->c_ispeed = termios_p->c_ospeed;
if ( (speed & ~CBAUD) != 0 || speed > _MAX_BAUD )
speed = BOTHER;
/*
* Don't set the input flags here; the B0 in c_cflag indicates that
* the input speed is tied to the output speed.
*/
termios_p->c_cflag = (termios_p->c_cflag & ~CBAUD) | speed;
return 0;
}
---
This allows us to adjust the baud rates to non-standard values using termios
interfaces without to resorting to add new headers and use a different API
(ioctl).
As Peter Anvin has indicated, he create a POC [1] with the aforementioned
new interfaces. It has not been rebased against master, more specially against
my termios refactor to simplify the multiple architecture header definitions,
but I intend to use as a base.
>
> 2019-04-09 Florian Weimer <fweimer at redhat.com>
>
> [BZ #10339]
> Linux: Define struct termios2 in <termios.h> under _GNU_SOURCE.
> * sysdeps/unix/sysv/linux/Makefile [$(subdir) == termios] (tests):
> Add tst-termios2.
> * sysdeps/unix/sysv/linux/tst-termios2.c: New file.
> * sysdeps/unix/sysv/linux/bits/termios2-struct.h: Likewise.
> * sysdeps/unix/sysv/linux/bits/termios.h [__USE_GNU]: Include it.
> * sysdeps/unix/sysv/linux/alpha/bits/termios2-struct.h: New file.
> * sysdeps/unix/sysv/linux/sparc/bits/termios2-struct.h: Likewise.
>
> diff --git a/NEWS b/NEWS
> index b58e2469d4..5e6ecb9c7d 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -18,6 +18,9 @@ Major new features:
>
> * On Linux, the gettid function has been added.
>
> +* On Linux, <termios.h> now provides a definition of struct termios2 with
> + the _GNU_SOURCE feature test macro.
> +
> * Minguo (Republic of China) calendar support has been added as an
> alternative calendar for the following locales: zh_TW, cmn_TW, hak_TW,
> nan_TW, lzh_TW.
> diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
> index 52ac6ad484..4cb5e4f0d2 100644
> --- a/sysdeps/unix/sysv/linux/Makefile
> +++ b/sysdeps/unix/sysv/linux/Makefile
> @@ -156,6 +156,7 @@ endif
>
> ifeq ($(subdir),termios)
> sysdep_headers += termio.h
> +tests += tst-termios2
> endif
>
> ifeq ($(subdir),posix)
> diff --git a/sysdeps/unix/sysv/linux/alpha/bits/termios2-struct.h b/sysdeps/unix/sysv/linux/alpha/bits/termios2-struct.h
> new file mode 100644
> index 0000000000..5f09445e23
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/alpha/bits/termios2-struct.h
> @@ -0,0 +1,33 @@
> +/* struct termios2 definition. Linux/alpha version.
> + Copyright (C) 2019 Free Software Foundation, Inc.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library. If not, see
> + <http://www.gnu.org/licenses/>. */
> +
> +#ifndef _TERMIOS_H
> +# error "Never include <bits/termios2-struct.h> directly; use <termios.h> instead."
> +#endif
> +
> +struct termios2
> +{
> + tcflag_t c_iflag;
> + tcflag_t c_oflag;
> + tcflag_t c_cflag;
> + tcflag_t c_lflag;
> + cc_t c_cc[NCCS];
> + cc_t c_line;
> + speed_t c_ispeed;
> + speed_t c_ospeed;
> +};
> diff --git a/sysdeps/unix/sysv/linux/bits/termios.h b/sysdeps/unix/sysv/linux/bits/termios.h
> index 997231cd03..45ac7affdf 100644
> --- a/sysdeps/unix/sysv/linux/bits/termios.h
> +++ b/sysdeps/unix/sysv/linux/bits/termios.h
> @@ -25,6 +25,10 @@ typedef unsigned int speed_t;
> typedef unsigned int tcflag_t;
>
> #include <bits/termios-struct.h>
> +#ifdef __USE_GNU
> +# include <bits/termios2-struct.h>
> +#endif
> +
> #include <bits/termios-c_cc.h>
> #include <bits/termios-c_iflag.h>
> #include <bits/termios-c_oflag.h>
> diff --git a/sysdeps/unix/sysv/linux/bits/termios2-struct.h b/sysdeps/unix/sysv/linux/bits/termios2-struct.h
> new file mode 100644
> index 0000000000..5a48e45ef3
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/bits/termios2-struct.h
> @@ -0,0 +1,33 @@
> +/* struct termios2 definition. Linux/generic version.
> + Copyright (C) 2019 Free Software Foundation, Inc.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library. If not, see
> + <http://www.gnu.org/licenses/>. */
> +
> +#ifndef _TERMIOS_H
> +# error "Never include <bits/termios2-struct.h> directly; use <termios.h> instead."
> +#endif
> +
> +struct termios2
> +{
> + tcflag_t c_iflag;
> + tcflag_t c_oflag;
> + tcflag_t c_cflag;
> + tcflag_t c_lflag;
> + cc_t c_line;
> + cc_t c_cc[NCCS];
> + speed_t c_ispeed;
> + speed_t c_ospeed;
> +};
> diff --git a/sysdeps/unix/sysv/linux/sparc/bits/termios2-struct.h b/sysdeps/unix/sysv/linux/sparc/bits/termios2-struct.h
> new file mode 100644
> index 0000000000..7c889e575c
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/sparc/bits/termios2-struct.h
> @@ -0,0 +1,33 @@
> +/* struct termios2 definition. Linux/sparc version.
> + Copyright (C) 2019 Free Software Foundation, Inc.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library. If not, see
> + <http://www.gnu.org/licenses/>. */
> +
> +#ifndef _TERMIOS_H
> +# error "Never include <bits/termios2-struct.h> directly; use <termios.h> instead."
> +#endif
> +
> +struct termios2
> +{
> + tcflag_t c_iflag;
> + tcflag_t c_oflag;
> + tcflag_t c_cflag;
> + tcflag_t c_lflag;
> + cc_t c_line;
> + cc_t c_cc[NCCS + 2];
> + speed_t c_ispeed;
> + speed_t c_ospeed;
> +};
> diff --git a/sysdeps/unix/sysv/linux/tst-termios2.c b/sysdeps/unix/sysv/linux/tst-termios2.c
> new file mode 100644
> index 0000000000..82326a1288
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/tst-termios2.c
> @@ -0,0 +1,48 @@
> +/* Minimal test of struct termios2 definition.
> + Copyright (C) 2019 Free Software Foundation, Inc.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library. If not, see
> + <http://www.gnu.org/licenses/>. */
> +
> +#include <termios.h>
> +#include <sys/ioctl.h>
> +
> +/* This function is never executed, but must be compiled successfully.
> + Accessing serial ports in the test suite is problematic because
> + they likely correspond with low-level system functionality. */
> +void
> +not_executed (int fd)
> +{
> + /* Avoid a compilation failure if TCGETS2, TCSETS2 are not
> + defined. */
> +#if defined (TCGETS2) && defined (TCSETS2)
> + struct termios2 ti;
> + ioctl (fd, TCGETS2, &ti);
> + ioctl (fd, TCSETS2, &ti);
> +#endif
> +}
> +
> +static int
> +do_test (void)
> +{
> + /* Fail at run time if TCGETS2 or TCSETS2 is not defined. */
> +#if defined (TCGETS2) && defined (TCSETS2)
> + return 0;
> +#else
> + return 1;
> +#endif
> +}
> +
> +#include <support/test-driver.c>
>
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