[PATCH 4/6 v9] fs: New helper legitimize_mntget() for getting a legitimize mnt

From: Kinglong Mee <kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
To: "J. Bruce Fields"
	<bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>,
	Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
Cc: "linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	NeilBrown <neilb-l3A5Bk7waGM@public.gmane.org>,
	Trond Myklebust
	<trond.myklebust-7I+n7zu2hftEKMMhf/gKZA@public.gmane.org>,
	kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
Subject: [PATCH 4/6 v9] fs: New helper legitimize_mntget() for getting a legitimize mnt
Date: Tue, 18 Aug 2015 15:21:59 +0800	[thread overview]
Message-ID: <55D2DD17.7050504@gmail.com> (raw)
In-Reply-To: <55D2DBF6.3010406-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

New helper legitimize_mntget for getting a mnt without setting
MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED, otherwise return NULL.

v9, Update using read_seqbegin_or_lock instead read_seqlock_excl

Signed-off-by: Kinglong Mee <kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 fs/namespace.c        | 30 ++++++++++++++++++++++++++++++
 include/linux/mount.h |  1 +
 2 files changed, 31 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index 2b8aa15..bf4a9f5 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1153,6 +1153,36 @@ struct vfsmount *mntget(struct vfsmount *mnt)
 }
 EXPORT_SYMBOL(mntget);
 
+struct vfsmount *legitimize_mntget(struct vfsmount *vfsmnt)
+{
+	struct mount *mnt;
+	unsigned seq = 0;
+
+	if (vfsmnt == NULL)
+		return NULL;
+retry:
+	read_seqbegin_or_lock(&mount_lock, &seq);
+
+	if (vfsmnt->mnt_flags & (MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED))
+		vfsmnt = NULL;
+	else if (need_seqretry(&mount_lock, seq))
+		goto retry;
+	else {
+		mnt = real_mount(vfsmnt);
+		mnt_add_count(mnt, 1);
+		if (need_seqretry(&mount_lock, seq) ||
+		    vfsmnt->mnt_flags & (MNT_SYNC_UMOUNT | MNT_UMOUNT |
+					 MNT_DOOMED)) {
+			mnt_add_count(mnt, -1);
+			goto retry;
+		}
+	}
+
+	done_seqretry(&mount_lock, seq);
+	return vfsmnt;
+}
+EXPORT_SYMBOL(legitimize_mntget);
+
 struct vfsmount *mnt_clone_internal(struct path *path)
 {
 	struct mount *p;
diff --git a/include/linux/mount.h b/include/linux/mount.h
index f822c3c..8ae9dc0 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -79,6 +79,7 @@ extern void mnt_drop_write(struct vfsmount *mnt);
 extern void mnt_drop_write_file(struct file *file);
 extern void mntput(struct vfsmount *mnt);
 extern struct vfsmount *mntget(struct vfsmount *mnt);
+extern struct vfsmount *legitimize_mntget(struct vfsmount *vfsmnt);
 extern struct vfsmount *mnt_clone_internal(struct path *path);
 extern int __mnt_is_readonly(struct vfsmount *mnt);
 
-- 
2.4.3

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