On Fri, Aug 24, 2018 at 10:45:31AM +0100, David Howells wrote:
> Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
>
> > I'm not against merging this patchset (have nits about resuing the
> > MS_* constants for the new API that I've complained about, but that's
> > really easy to fix before -final),
>
> Can you send me a patch that does what you want here? They're only used by
> fsmount() for creating a vfsmount and not used for the superblock creation or
> reconfiguration.
I'm bothered by the fact that we use the same MS_ prefix in the old mount(2) api
and the new fsmount(2) api. 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.
Also notice, how the old code just totally ignored MS_RELATIME? Bit of rot in
the new interface already.
So here's a patch. The MNT_ prefix is already used by libmount, and we don't
want any confusion arising from that. So how about M_*? Short and sweet, just
like O_* for open(2).
Reusing the same values as MNT_ isn't important, but it does reduce the code
size a bit. Especially if we'd switch to MNT_STRICTATIME internally as well.
Thanks,
Miklos
---
diff --git a/fs/namespace.c b/fs/namespace.c
index e34e3fd064b0..a4b8503f80b8 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3351,7 +3351,7 @@ 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;
@@ -3366,27 +3366,21 @@ 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_NOSUID | M_NODEV | M_NOEXEC | M_NOATIME |
+ M_NODIRATIME | M_STRICTATIME | M_RDONLY))
return -EINVAL;
- if (ms_flags & MS_RDONLY)
- mnt_flags |= MNT_READONLY;
- if (ms_flags & MS_NOSUID)
- mnt_flags |= MNT_NOSUID;
- if (ms_flags & MS_NODEV)
- mnt_flags |= MNT_NODEV;
- if (ms_flags & MS_NOEXEC)
- mnt_flags |= MNT_NOEXEC;
- if (ms_flags & MS_NODIRATIME)
- mnt_flags |= MNT_NODIRATIME;
+ BUILD_BUG_ON(M_NOSUID != MNT_NOSUID || M_NODEV != MNT_NODEV ||
+ M_NOEXEC != MNT_NOEXEC || M_NOATIME != MNT_NOATIME ||
+ M_NODIRATIME != MNT_NODIRATIME ||
+ M_STRICTATIME != MNT_RELATIME || M_RDONLY != MNT_READONLY);
+
+ /* Relatime is the default, but internally that's what we flag */
+ mnt_flags = m_flags & ~M_STRICTATIME;
- if (ms_flags & MS_STRICTATIME) {
- if (ms_flags & MS_NOATIME)
+ if (m_flags & M_STRICTATIME) {
+ if (m_flags & M_NOATIME)
return -EINVAL;
- } else if (ms_flags & MS_NOATIME) {
- mnt_flags |= MNT_NOATIME;
} else {
mnt_flags |= MNT_RELATIME;
}
diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
index 3634e065836c..331e69f5a7bf 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_NOSUID 0x01
+#define M_NODEV 0x02
+#define M_NOEXEC 0x04
+#define M_NOATIME 0x08
+#define M_NODIRATIME 0x10
+#define M_STRICTATIME 0x20
+#define M_RDONLY 0x40
+
/*
* These are the fs-independent mount-flags: up to 32 flags are supported
*
