[CRIU] [PATCH 05/15] tty: Fetch ctty index based on sid

[Cyrill Gorcunov]

If /dev/tty opened migrating to another process via scm
or say it left opened while new controlling terminal is
being set up, we will obtain sid = 0 here and should not
proceed dumping. The proper support for such schemes
requires kernel pathching (most likely we will need to
alter kcmp syscall to find underlied pty peer).

Still if an application opens /dev/tty several times
its tty-info should point to same entry thus we generate
index based on sid.

n.b. the parasite_dump_tty is called twice for cttys,
so need to optimize, left as is for now to minimize
code changes.

Signed-off-by: Cyrill Gorcunov <gorcunov at gmail.com>
---
 criu/tty.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 51 insertions(+), 3 deletions(-)

diff --git a/criu/tty.c b/criu/tty.c
index fcf73917d087..9d65e0d54a53 100644
--- a/criu/tty.c
+++ b/criu/tty.c
@@ -131,11 +131,11 @@ static int self_stdin_fdid = -1;
  * If this won't be enough in future we simply need to
  * change tracking mechanism to some more extendable.
  *
- * This particular bitmap requires 256 bytes of memory.
+ * This particular bitmap requires 512 bytes of memory.
  * Pretty acceptable trade off in a sake of simplicity.
  */
 
-#define MAX_TTYS	1024
+#define MAX_TTYS	2048
 
 /*
  * Custom indices should be even numbers just in case if we
@@ -148,6 +148,10 @@ static int self_stdin_fdid = -1;
 #define CTTY_INDEX	1006
 #define ETTY_INDEX	1008
 #define STTY_INDEX	1010
+
+#define MIN_CTTY_INDEX	1012
+#define MAX_CTTY_INDEX	2002
+
 #define INDEX_ERR	(MAX_TTYS + 1)
 
 static DECLARE_BITMAP(tty_bitmap, (MAX_TTYS << 1));
@@ -208,10 +212,51 @@ static struct tty_driver console_driver = {
 	.open			= open_simple_tty,
 };
 
+static int ctty_fd_get_index(int fd, const struct fd_parms *p)
+{
+	static unsigned int next_index = 0;
+	struct parasite_tty_args *pti;
+	struct tty_dump_info *dinfo;
+
+	pti = parasite_dump_tty(p->fd_ctl, p->fd, TTY_TYPE__CTTY);
+	if (!pti) {
+		pr_err("Can't fetch tty params\n");
+		return INDEX_ERR;
+	}
+
+	if (!pti->sid) {
+		pr_err("Can't fetch tty SID\n");
+		return INDEX_ERR;
+	}
+
+	list_for_each_entry(dinfo, &all_ttys, list) {
+		if (dinfo->driver->type != TTY_TYPE__CTTY)
+			continue;
+		if (dinfo->sid == pti->sid)
+			return dinfo->index;
+	}
+
+	if (next_index < MAX_CTTY_INDEX)
+		return MIN_CTTY_INDEX + next_index++;
+
+	pr_err("Index for /dev/tty is too big\n");
+	return INDEX_ERR;
+}
+
+static int ctty_img_get_index(struct tty_info *ti)
+{
+	/*
+	 * On restore we don't care about index, because
+	 * sessions restore goes via pty driver.
+	 */
+	return CTTY_INDEX;
+}
+
 static struct tty_driver ctty_driver = {
 	.type			= TTY_TYPE__CTTY,
 	.name			= "ctty",
-	.index			= CTTY_INDEX,
+	.fd_get_index		= ctty_fd_get_index,
+	.img_get_index		= ctty_img_get_index,
 	.open			= open_simple_tty,
 };
 
@@ -1941,6 +1986,9 @@ static int dump_tty_info(int lfd, uint32_t id, const struct fd_parms *p,
 			return -1;
 		}
 		dinfo->index	= index;
+	} else if (is_ctty(driver)) {
+		dinfo->index	= index;
+		dinfo->lfd	= -1;
 	} else {
 		dinfo->index	= -1;
 		dinfo->lfd	= -1;
-- 
2.17.1