linux-kernel - Q: On restoring terminal with hinted index

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Date:	Wed, 15 Aug 2012 19:25:04 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Q: On restoring terminal with hinted index

Hi Peter,

that happened that in a sake of restoring ptys after checkpoint
we need to create them with predefined indices, as they were at
moment of dumping. So we have two options -- 1) Open terminals
in sequence until needed index reached 2) Use some other way to
say the kernel that some index is preferred.

So I thought, would it be acceptible to provide such hint via
sysctl, as in patch below (note I've not even compiled it yet,
but would like to know your opinion early).

(Maybe even make it one shot, thus once ida_get_new_above called
 the pty_next reset to zero).

---
 fs/devpts/inode.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

Index: linux-2.6.git/fs/devpts/inode.c
===================================================================
--- linux-2.6.git.orig/fs/devpts/inode.c
+++ linux-2.6.git/fs/devpts/inode.c
@@ -45,6 +45,7 @@ static int pty_reserve = NR_UNIX98_PTY_R
 static int pty_limit_min;
 static int pty_limit_max = INT_MAX;
 static int pty_count;
+static int pty_next;
 
 static struct ctl_table pty_table[] = {
 	{
@@ -69,6 +70,12 @@ static struct ctl_table pty_table[] = {
 		.mode		= 0444,
 		.data		= &pty_count,
 		.proc_handler	= proc_dointvec,
+	}, {
+		.procname	= "next",
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.data		= &pty_next,
+		.proc_handler	= proc_dointvec,
 	},
 	{}
 };
@@ -516,7 +523,7 @@ retry:
 		return -ENOSPC;
 	}
 
-	ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
+	ida_ret = ida_get_new_above(&fsi->allocated_ptys, pty_next, &index);
 	if (ida_ret < 0) {
 		mutex_unlock(&allocated_ptys_lock);
 		if (ida_ret == -EAGAIN)
--
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