diff options
| author | Nicolas Pitre <npitre@baylibre.com> | 2025-05-20 13:16:44 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-05-21 13:41:03 +0200 |
| commit | 81cf4d7d2379df853a0cbb8486286783c7380ac3 (patch) | |
| tree | daaf4816506e0dd8fea34520c79bc07d76876cdd | |
| parent | 80fa7a03378588582eb40f89b6f418c0c256cf24 (diff) | |
vt: add VT_GETCONSIZECSRPOS to retrieve console size and cursor position
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>
| -rw-r--r-- | drivers/tty/vt/vt_ioctl.c | 16 | ||||
| -rw-r--r-- | include/uapi/linux/vt.h | 11 |
2 files changed, 27 insertions, 0 deletions
diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c index 1f2bdd2e1cc5..61342e06970a 100644 --- a/drivers/tty/vt/vt_ioctl.c +++ b/drivers/tty/vt/vt_ioctl.c @@ -951,6 +951,22 @@ int vt_ioctl(struct tty_struct *tty, (unsigned short __user *)arg); case VT_WAITEVENT: return vt_event_wait_ioctl((struct vt_event __user *)arg); + + case VT_GETCONSIZECSRPOS: + { + struct vt_consizecsrpos concsr; + + console_lock(); + concsr.con_cols = vc->vc_cols; + concsr.con_rows = vc->vc_rows; + concsr.csr_col = vc->state.x; + concsr.csr_row = vc->state.y; + console_unlock(); + if (copy_to_user(up, &concsr, sizeof(concsr))) + return -EFAULT; + return 0; + } + default: return -ENOIOCTLCMD; } diff --git a/include/uapi/linux/vt.h b/include/uapi/linux/vt.h index e9d39c48520a..e5b0c492aa18 100644 --- a/include/uapi/linux/vt.h +++ b/include/uapi/linux/vt.h @@ -2,6 +2,8 @@ #ifndef _UAPI_LINUX_VT_H #define _UAPI_LINUX_VT_H +#include <linux/ioctl.h> +#include <linux/types.h> /* * These constants are also useful for user-level apps (e.g., VC @@ -84,4 +86,13 @@ struct vt_setactivate { #define VT_SETACTIVATE 0x560F /* Activate and set the mode of a console */ +/* get console size and cursor position */ +struct vt_consizecsrpos { + __u16 con_rows; /* number of console rows */ + __u16 con_cols; /* number of console columns */ + __u16 csr_row; /* current cursor's row */ + __u16 csr_col; /* current cursor's column */ +}; +#define VT_GETCONSIZECSRPOS _IOR('V', 0x10, struct vt_consizecsrpos) + #endif /* _UAPI_LINUX_VT_H */ |