linux-ext4 - [PATCH 02/12] container quota: lock/unlock mount namespace when performing quotactl.

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Date:	Wed, 30 May 2012 22:58:56 +0800
From:	jeff.liu@...cle.com
To:	containers@...ts.linux-foundation.org
Cc:	cgroups@...r.kernel.org, jack@...e.cz, glommer@...allels.com,
	daniel.lezcano@...e.fr, tytso@....edu, bpm@....com,
	chris.mason@...cle.com, hch@...radead.org,
	christopher.jones@...cle.com, david@...morbit.com,
	tinguely@....com, tm@....ma, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, Jie Liu <jeff.liu@...cle.com>
Subject: [PATCH 02/12] container quota: lock/unlock mount namespace when performing quotactl.

Introduce two functions to lock/unlock a particular mount namespace
when container quota operations is performed.

Signed-off-by: Jie Liu <jeff.liu@...cle.com>
---
 fs/namespace.c                |   17 +++++++++++++++++
 include/linux/mnt_namespace.h |   13 +++++++++++++
 2 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index e608199..8823ba8 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2633,3 +2633,20 @@ bool our_mnt(struct vfsmount *mnt)
 {
 	return check_mnt(real_mount(mnt));
 }
+
+/*
+ * Lock the mount namespace when performing a particular container
+ * disk quotactl operation, especially to protect removing it.
+ */
+void lock_mnt_ns(struct mnt_namespace *ns)
+{
+	down_write(&namespace_sem);
+}
+
+/*
+ * Unlock the mount namespace after quotactl on that was done.
+ */
+void unlock_mnt_ns(struct mnt_namespace *ns)
+{
+	up_write(&namespace_sem);
+}
diff --git a/include/linux/mnt_namespace.h b/include/linux/mnt_namespace.h
index 5a8e390..ff72ed5 100644
--- a/include/linux/mnt_namespace.h
+++ b/include/linux/mnt_namespace.h
@@ -9,6 +9,19 @@ extern struct mnt_namespace *copy_mnt_ns(unsigned long, struct mnt_namespace *,
 		struct fs_struct *);
 extern void put_mnt_ns(struct mnt_namespace *ns);
 
+#ifdef CONFIG_NS_QUOTA
+extern void lock_mnt_ns(struct mnt_namespace *);
+extern void unlock_mnt_ns(struct mnt_namespace *);
+#else
+void lock_mnt_ns(struct mnt_namespace *)
+{
+}
+
+void unlock_mnt_ns(struct mnt_namespace *)
+{
+}
+#endif
+
 extern const struct file_operations proc_mounts_operations;
 extern const struct file_operations proc_mountinfo_operations;
 extern const struct file_operations proc_mountstats_operations;
-- 
1.7.9

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