SchOS/cmd/chvt/main.c

// SPDX-License-Identifier: GPL-2.0-or-later
//
// chvt N -- show virtual terminal N.
//
// The same name and the same argument as the Linux tool, because it does the
// same thing and nobody should have to learn a second one. The chord does
// this from the keyboard; this does it from a script, and from a serial
// console where there are no function keys to press.
//
//   chvt              report the active terminal, those in use, and the chord
//   chvt 2            switch to /dev/tty2
//   chvt -c <spec>    set the switch chord
//   chvt -c off       unbind it entirely; chvt stays the only way to switch
//
// The chord is settable because the right value is a property of the *host*,
// not of SchOS. A display manager that grabs Ctrl+Alt+F<n> takes it before the
// guest sees anything, and it matches loosely -- extra modifiers do not get
// past it -- so a chord that works on one machine is dead on the next. The
// guest cannot detect this: a key the host swallowed is indistinguishable from
// a key nobody pressed. So it is a setting.
//
//   chvt -c altgr+F           AltGr+F1..F6        (the default)
//   chvt -c ctrl+shift+F      Ctrl+Shift+F1..F6
//   chvt -c alt+1             Alt+1..6
//   chvt -c off               no chord at all
//
// Whatever the modifiers are, they also bind minus and equals to the previous
// and next terminal in use -- AltGr+- and AltGr+= by default.

#include "core/types.h"
#include "uapi/user.h"
#include "uapi/fcntl.h"
#include "uapi/posix.h"

// No printf in lib/, and this needs one string and two small numbers.
static void
puts(const char *s)
{
    int n = 0;
    while (s[n]) n++;
    write(1, (void *)s, n);
}

static void
putn(int v)
{
    char b[12];
    int i = 0;
    if (v < 0) { write(1, "-", 1); v = -v; }
    if (v == 0) { write(1, "0", 1); return; }
    while (v > 0) { b[i++] = '0' + (v % 10); v /= 10; }
    while (i-- > 0) write(1, &b[i], 1);
}

static int
num(const char *s)
{
    int v = 0;
    while (*s >= '0' && *s <= '9')
        v = v * 10 + (*s++ - '0');
    return v;
}

static int
same(const char *a, const char *b, int n)
{
    for (int i = 0; i < n; i++)
        if (a[i] != b[i]) return 0;
    return 1;
}

static int
eq(const char *a, const char *b)
{
    while (*a && *a == *b) { a++; b++; }
    return *a == 0 && *b == 0;
}

// "ctrl+shift+F", "alt+1", "off". Modifiers by name, then a base: F for the
// function keys, 1 for the number row.
static int
parse_chord(const char *spec, struct vt_chord *out)
{
    out->mods = 0;
    out->base = 0;

    if (eq(spec, "off") || eq(spec, "none"))
        return 1;                      // no modifiers: the chord is disabled

    const char *p = spec;
    while (*p) {
        const char *start = p;
        while (*p && *p != '+') p++;
        int n = (int)(p - start);

        if      (n == 4 && same(start, "ctrl",  4)) out->mods |= VTC_CTRL;
        else if (n == 5 && same(start, "shift", 5)) out->mods |= VTC_SHIFT;
        else if (n == 3 && same(start, "alt",   3)) out->mods |= VTC_ALT;
        else if (n == 5 && same(start, "altgr", 5)) out->mods |= VTC_RALT;
        else if (n == 1 && (*start == 'F' || *start == 'f')) out->base = VTC_BASE_F1;
        else if (n == 1 && *start == '1')                    out->base = VTC_BASE_1;
        else return 0;

        if (*p == '+') p++;
    }
    // A base with no modifiers would bind a bare function key, which every
    // full-screen program wants. Refuse it here rather than in the kernel, so
    // the message can say why.
    if (out->base && !out->mods)
        return 0;
    if (out->mods && !out->base)
        out->base = VTC_BASE_F1;
    return 1;
}

static void
show_chord(const struct vt_chord *c)
{
    if (c->mods == 0) {
        puts("off (use chvt N)\n");
        return;
    }
    if (c->mods & VTC_CTRL)  puts("Ctrl+");
    if (c->mods & VTC_ALT)   puts("Alt+");
    if (c->mods & VTC_SHIFT) puts("Shift+");
    if (c->mods & VTC_RALT)  puts("AltGr+");
    if (c->base == VTC_BASE_F1) puts("F1..F6");
    else                        puts("1..6");
    puts(", and ");
    if (c->mods & VTC_CTRL)  puts("Ctrl+");
    if (c->mods & VTC_ALT)   puts("Alt+");
    if (c->mods & VTC_SHIFT) puts("Shift+");
    if (c->mods & VTC_RALT)  puts("AltGr+");
    puts("- / + to step\n");
}

int
main(int argc, char *argv[])
{
    // /dev/console rather than fd 0: the caller may have redirected its input,
    // and the terminal being asked about is the machine's, not whichever one
    // this process happens to be reading from.
    int fd = open("/dev/console", O_RDWR);
    if (fd < 0) {
        puts("chvt: cannot open /dev/console\n");
        exit();
    }

    if (argc == 3 && argv[1][0] == '-' && argv[1][1] == 'c') {
        struct vt_chord c;
        if (!parse_chord(argv[2], &c)) {
            puts("chvt: bad chord -- try ctrl+shift+F, alt+1, or off\n");
            exit();
        }
        if (ioctl(fd, VT_SETCHORD, &c) < 0) {
            puts("chvt: kernel refused that chord\n");
            exit();
        }
        puts("chord set to ");
        show_chord(&c);
        exit();
    }

    if (argc == 1) {
        struct vt_stat st;
        if (ioctl(fd, VT_GETSTATE, &st) < 0) {
            puts("chvt: VT_GETSTATE failed\n");
            exit();
        }
        puts("active: tty");
        putn(st.v_active);
        puts("\nin use:");
        for (int i = 1; i <= 16; i++)
            if (st.v_state & (1 << i)) {
                puts(" tty");
                putn(i);
            }
        puts("\n");
        struct vt_chord c;
        if (ioctl(fd, VT_GETCHORD, &c) == 0) {
            puts("chord:  ");
            show_chord(&c);
        }
        exit();
    }

    int n = num(argv[1]);
    if (n < 1) {
        puts("usage: chvt N\n");
        exit();
    }

    // The argument goes by value, not through a pointer -- Linux defines
    // VT_ACTIVATE that way and so does SchOS. Passing a pointer here would
    // switch to whatever the address happened to be.
    if (ioctl(fd, VT_ACTIVATE, (void *)(long)n) < 0) {
        puts("chvt: no terminal ");
        putn(n);
        puts("\n");
        exit();
    }
    exit();
}