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The console dimension and cursor position are available through the
/dev/vcsa interface already. However the /dev/vcsa header format uses
single-byte fields therefore those values are clamped to 255.
As surprizing as this may seem, some people do use 240-column 67-row
screens (a 1920x1080 monitor with 8x16 pixel fonts) which is getting
close to the limit. Monitors with higher resolution are not uncommon
these days (3840x2160 producing a 480x135 character display) and it is
just a matter of time before someone with, say, a braille display using
the Linux VT console and BRLTTY on such a screen reports a bug about
missing and oddly misaligned screen content.
Let's add VT_GETCONSIZECSRPOS for the retrieval of console size and cursor
position without byte-sized limitations. The actual console size limit as
encoded in vt.c is 32767x32767 so using a short here is appropriate. Then
this can be used to get the cursor position when /dev/vcsa reports 255.
The screen dimension may already be obtained using TIOCGWINSZ and adding
the same information to VT_GETCONSIZECSRPOS might be redundant. However
applications that care about cursor position also care about display
size and having 2 separate system calls to obtain them separately is
wasteful. Also, the cursor position can be queried by writing "\e[6n" to
a tty and reading back the result but that may be done only by the actual
application using that tty and not a sideline observer.
Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
Link: https://lore.kernel.org/r/20250520171851.1219676-3-nico@fluxnic.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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license
Many user space API headers are missing licensing information, which
makes it hard for compliance tools to determine the correct license.
By default are files without license information under the default
license of the kernel, which is GPLV2. Marking them GPLV2 would exclude
them from being included in non GPLV2 code, which is obviously not
intended. The user space API headers fall under the syscall exception
which is in the kernels COPYING file:
NOTE! This copyright does *not* cover user programs that use kernel
services by normal system calls - this is merely considered normal use
of the kernel, and does *not* fall under the heading of "derived work".
otherwise syscall usage would not be possible.
Update the files which contain no license information with an SPDX
license identifier. The chosen identifier is 'GPL-2.0 WITH
Linux-syscall-note' which is the officially assigned identifier for the
Linux syscall exception. SPDX license identifiers are a legally binding
shorthand, which can be used instead of the full boiler plate text.
This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne. See the previous patch in this series for the
methodology of how this patch was researched.
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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MAX_NR_CONSOLES and MAX_NR_USER_CONSOLES are both 63 since they were
introduced in 1.1.54. And since vc_allocate does:
if (currcons >= MAX_NR_CONSOLES)
return -ENXIO;
if (!vc_cons[currcons].d) {
if (currcons >= MAX_NR_USER_CONSOLES && !capable(CAP_SYS_RESOURCE))
return -EPERM;
}
the second check is pointless. Remove both the check and the macro
MAX_NR_USER_CONSOLES.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Reported-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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vt_get_kmsg_redirect() only has meaning to the console driver as
an alias for calling vt_kmsg_redirect(). Move the macro definition
to the only source file which uses it; remove from uapi/linux/vt.h
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Michael Kerrisk <mtk.manpages@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Dave Jones <davej@redhat.com>
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