activevt: initHEAD1.1.0master

2 files changed, 75 insertions, 3 deletions

diff --git a/Makefile b/Makefile
index 14ffa64..cee9a29 100644
--- a/Makefile
+++ b/Makefile
@@ -2,13 +2,17 @@ PREFIX ?= /usr/local
 BINDIR ?= $(PREFIX)/bin
 CACHEDIR ?= $(PWD)
 
+UTILS := activevt exec
+
+BUILT_UTILS := $(addprefix $(CACHEDIR)/,$(UTILS))
+
 .PHONY: all
-all: $(CACHEDIR)/exec
+all: $(BUILT_UTILS)
 
 .PHONY: install
-install: $(CACHEDIR)/exec
+install: $(BUILT_UTILS)
 	mkdir -p $(BINDIR)
-	cp $(CACHEDIR)/exec $(BINDIR)/
+	cp $^ $(BINDIR)/
 
 $(CACHEDIR)/%: %.c
 	gcc -Wall -Os -o $@ $<
diff --git a/activevt.c b/activevt.c
new file mode 100644
index 0000000..01790f9
--- /dev/null
+++ b/activevt.c
@@ -0,0 +1,68 @@
+#include <ctype.h>
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/vt.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+// check if argument is tty[0-9]
+static bool is_vt_basename(const char *s) {
+    return !strncmp(s, "tty", 3) && isdigit(s[3]);
+}
+
+// return the number of the active virtual terminal or -1 on error
+static int get_active_vt() {
+    int dfd = open("/dev", O_RDONLY | O_DIRECTORY);
+    if (dfd < 0) {
+        perror("open /dev");
+        return 1;
+    }
+
+    DIR *d = fdopendir(dfd);
+    if (!d) {
+        perror("fdopendir");
+        close(dfd);
+        return 1;
+    }
+
+    int active_vt = -1;
+    struct dirent *ent;
+
+    while ((ent = readdir(d)) != NULL) {
+        if (!is_vt_basename(ent->d_name))
+            continue;
+
+        int fd = openat(dfd, ent->d_name, O_RDONLY | O_NONBLOCK);
+        if (fd < 0)
+            continue;
+
+        struct vt_stat state;
+        if (ioctl(fd, VT_GETSTATE, &state) == 0) {
+            active_vt = state.v_active;
+            close(fd);
+            break;
+        }
+
+        close(fd);
+    }
+
+    closedir(d);
+
+    return active_vt;
+}
+
+int main(void) {
+    int active_vt = get_active_vt();
+
+    if (active_vt < 0) {
+        fprintf(stderr, "Could not determine active VT\n");
+        return 1;
+    }
+
+    printf("%d\n", active_vt);
+    return 0;
+}