From: Miklos Szeredi Subject: statx: add mount_root Determining whether a path or file descriptor refers to a mountpoint (or more precisely a mount root) is not trivial using current tools. Add a flag to statx that indicates whether the path or fd refers to the root of a mount or not. Reported-by: Lennart Poettering Reported-by: J. Bruce Fields Signed-off-by: Miklos Szeredi --- fs/stat.c | 3 +++ include/uapi/linux/stat.h | 1 + 2 files changed, 4 insertions(+) --- a/include/uapi/linux/stat.h +++ b/include/uapi/linux/stat.h @@ -172,6 +172,7 @@ struct statx { #define STATX_ATTR_NODUMP 0x00000040 /* [I] File is not to be dumped */ #define STATX_ATTR_ENCRYPTED 0x00000800 /* [I] File requires key to decrypt in fs */ #define STATX_ATTR_AUTOMOUNT 0x00001000 /* Dir: Automount trigger */ +#define STATX_ATTR_MOUNT_ROOT 0x00002000 /* Root of a mount */ #define STATX_ATTR_VERITY 0x00100000 /* [I] Verity protected file */ --- a/fs/stat.c +++ b/fs/stat.c @@ -202,6 +202,9 @@ int vfs_statx(int dfd, const char __user error = vfs_getattr(&path, stat, request_mask, flags); stat->mnt_id = real_mount(path.mnt)->mnt_id; stat->result_mask |= STATX_MNT_ID; + if (path.mnt->mnt_root == path.dentry) + stat->attributes |= STATX_ATTR_MOUNT_ROOT; + stat->attributes_mask |= STATX_ATTR_MOUNT_ROOT; path_put(&path); if (retry_estale(error, lookup_flags)) { lookup_flags |= LOOKUP_REVAL;