linux-kernel - [PATCH 5/6] fsmount: do not use legacy MS

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Date:   Thu, 20 Sep 2018 17:12:13 +0200
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Al Viro <viro@...IV.linux.org.uk>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 5/6] fsmount: do not use legacy MS_ flags

What happens if we introduce new flags for fsmount(2) and are already out
of flags for mount(2)?  I see a big mess that way.

So let's instead start a clean new set, to be used in the new API.

The MS_RELATIME flag was accepted but ignored.  Simply leave this out of
the new set, since "relatime" is the default.

The MNT_ prefix is already used by libmount, and we don't want any
confusion arising from that.  MOUNT_ feels a bit too long, so just go with
the short and sweet M_ prefix.

Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
---
 fs/namespace.c             | 28 +++++++++++++---------------
 include/uapi/linux/mount.h |  9 +++++++++
 2 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 7671c1f6fc22..027b99b993c0 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3332,7 +3332,7 @@ EXPORT_SYMBOL_GPL(kern_mount);
  * Create a kernel mount representation for a new, prepared superblock
  * (specified by fs_fd) and attach to an open_tree-like file descriptor.
  */
-SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags, unsigned int, ms_flags)
+SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags, unsigned int, m_flags)
 {
 	struct fs_context *fc;
 	struct file *file;
@@ -3347,30 +3347,28 @@ SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags, unsigned int, ms_flags
 	if ((flags & ~(FSMOUNT_CLOEXEC)) != 0)
 		return -EINVAL;
 
-	if (ms_flags & ~(MS_RDONLY | MS_NOSUID | MS_NODEV | MS_NOEXEC |
-			 MS_NOATIME | MS_NODIRATIME | MS_RELATIME |
-			 MS_STRICTATIME))
+	if (m_flags & ~(M_RDONLY | M_NOSUID | M_NODEV | M_NOEXEC |
+			 M_NOATIME | M_STRICTATIME | M_NODIRATIME))
 		return -EINVAL;
 
-	if (ms_flags & MS_RDONLY)
+	if ((m_flags & M_STRICTATIME) && (m_flags & M_NOATIME))
+		return -EINVAL;
+
+	if (m_flags & M_RDONLY)
 		mnt_flags |= MNT_READONLY;
-	if (ms_flags & MS_NOSUID)
+	if (m_flags & M_NOSUID)
 		mnt_flags |= MNT_NOSUID;
-	if (ms_flags & MS_NODEV)
+	if (m_flags & M_NODEV)
 		mnt_flags |= MNT_NODEV;
-	if (ms_flags & MS_NOEXEC)
+	if (m_flags & M_NOEXEC)
 		mnt_flags |= MNT_NOEXEC;
-	if (ms_flags & MS_NODIRATIME)
+	if (m_flags & M_NODIRATIME)
 		mnt_flags |= MNT_NODIRATIME;
 
-	if (ms_flags & MS_STRICTATIME) {
-		if (ms_flags & MS_NOATIME)
-			return -EINVAL;
-	} else if (ms_flags & MS_NOATIME) {
+	if (m_flags & M_NOATIME)
 		mnt_flags |= MNT_NOATIME;
-	} else {
+	else if (!(m_flags & M_STRICTATIME))
 		mnt_flags |= MNT_RELATIME;
-	}
 
 	f = fdget(fs_fd);
 	if (!f.file)
diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
index 3634e065836c..fce3513fc242 100644
--- a/include/uapi/linux/mount.h
+++ b/include/uapi/linux/mount.h
@@ -1,6 +1,15 @@
 #ifndef _UAPI_LINUX_MOUNT_H
 #define _UAPI_LINUX_MOUNT_H
 
+/* Mount flags passed to fsmount(2) */
+#define M_RDONLY	0x01
+#define M_NOSUID	0x02
+#define M_NODEV		0x04
+#define M_NOEXEC	0x08
+#define M_NOATIME	0x10
+#define M_STRICTATIME	0x20
+#define M_NODIRATIME	0x40
+
 /*
  * These are the fs-independent mount-flags: up to 32 flags are supported
  *
-- 
2.14.3