Currently userspace can only determine whether a mountpoint is private
by parsing /proc/<pid>/mountinfo. It would be convenient to simply retrieve
this property with a statvfs() call.
This let's userspace avoid costly parsing, supports cases where /proc is
not mounted, and supports usecases where file descriptors to mountpoints are
passed between processes that are inspected via fstatvfs().
A mountpoint is considered ST_PRIVATE iff and it is neither ST_SLAVE nor
ST_SHARED.
Signed-off-by: Christian Brauner <christ...@brauner.io>
---
v0->v1:
* non-functional changes: extend commit message
---
fs/statfs.c | 2 ++
include/linux/statfs.h | 1 +
2 files changed, 3 insertions(+)
diff --git a/fs/statfs.c b/fs/statfs.c
index 35ad0402c9a3..899e899ee84c 100644
--- a/fs/statfs.c
+++ b/fs/statfs.c
@@ -58,6 +58,8 @@ static int calculate_f_flags(struct vfsmount *mnt)
if (IS_MNT_SLAVE(real_mount(mnt)))
flags |= ST_SLAVE;
+ else if (!(flags & ST_SHARED))
+ flags |= ST_PRIVATE;
return flags;
}
diff --git a/include/linux/statfs.h b/include/linux/statfs.h
index 048127effaad..663fa5498a7d 100644
--- a/include/linux/statfs.h
+++ b/include/linux/statfs.h
@@ -41,6 +41,7 @@ struct kstatfs {
#define ST_NODIRATIME (1<<11) /* do not update directory access times */
#define ST_RELATIME (1<<12) /* update atime relative to mtime/ctime */
#define ST_UNBINDABLE (1<<17) /* change to unbindable */
+#define ST_PRIVATE (1<<18) /* change to private */
#define ST_SLAVE (1<<19) /* change to slave */
#define ST_SHARED (1<<20) /* change to shared */
--
2.17.0
