From: Jens Axboe <jens.axboe@oracle.com>
Date: Thu, 24 Jan 2008 07:54:47 +0000 (+0100)
Subject: kernel: add CLONE_IO to specifically request sharing of IO contexts
X-Git-Tag: v2.6.25-rc1~1174^2~2
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fadad878cc0640cc9cd5569998bf54b693f7b38b;p=linux-2.6

kernel: add CLONE_IO to specifically request sharing of IO contexts

syslets (or other threads/processes that want io context sharing) can
set this to enforce sharing of io context.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 80837e7d52..2d0546e884 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -27,6 +27,7 @@
 #define CLONE_NEWUSER		0x10000000	/* New user namespace */
 #define CLONE_NEWPID		0x20000000	/* New pid namespace */
 #define CLONE_NEWNET		0x40000000	/* New network namespace */
+#define CLONE_IO		0x80000000	/* Clone io context */
 
 /*
  * Scheduling policies
diff --git a/kernel/fork.c b/kernel/fork.c
index 1987c57abb..314f5101d2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -792,15 +792,21 @@ out:
 	return error;
 }
 
-static int copy_io(struct task_struct *tsk)
+static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
 {
 #ifdef CONFIG_BLOCK
 	struct io_context *ioc = current->io_context;
 
 	if (!ioc)
 		return 0;
-
-	if (ioprio_valid(ioc->ioprio)) {
+	/*
+	 * Share io context with parent, if CLONE_IO is set
+	 */
+	if (clone_flags & CLONE_IO) {
+		tsk->io_context = ioc_task_link(ioc);
+		if (unlikely(!tsk->io_context))
+			return -ENOMEM;
+	} else if (ioprio_valid(ioc->ioprio)) {
 		tsk->io_context = alloc_io_context(GFP_KERNEL, -1);
 		if (unlikely(!tsk->io_context))
 			return -ENOMEM;
@@ -1176,7 +1182,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 		goto bad_fork_cleanup_mm;
 	if ((retval = copy_namespaces(clone_flags, p)))
 		goto bad_fork_cleanup_keys;
-	if ((retval = copy_io(p)))
+	if ((retval = copy_io(clone_flags, p)))
 		goto bad_fork_cleanup_namespaces;
 	retval = copy_thread(0, clone_flags, stack_start, stack_size, p, regs);
 	if (retval)