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terminal: Explain FreeBSD current_vt behavior

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This commit is contained in:
Kenny Levinsen 2020-08-28 15:27:58 +00:00
parent dbdce8a54b
commit 27c1914625
1 changed files with 25 additions and 0 deletions
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25
common/terminal.c
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@ -138,6 +138,31 @@ int terminal_current_vt(int fd) {
log_errorf("could not retrieve VT state: %s", strerror(errno)); log_errorf("could not retrieve VT state: %s", strerror(errno));
return -1; return -1;
} }
// The FreeBSD VT_GETACTIVE is implemented in the kernel as follows:
//
// static int
// vtterm_ioctl(struct terminal *tm, u_long cmd, caddr_t data,
// struct thread *td)
// {
// struct vt_window *vw = tm->tm_softc;
// struct vt_device *vd = vw->vw_device;
// ...
// switch (cmd) {
// ...
// case VT_GETACTIVE:
// *(int *)data = vd->vd_curwindow->vw_number + 1;
// return (0);
// ...
// }
// ...
// }
//
// The side-effect here being that the returned VT number is one
// greater than the internal VT number, which is what is used for e.g.
// numbering the associated VT. To simplify things, we subtract one
// from the returned VT number before returning it.
if (vt < 1) { if (vt < 1) {
log_errorf("invalid vt: %d", vt); log_errorf("invalid vt: %d", vt);
return -1; return -1;