On 28/05/2019 16:12, David Howells wrote:
Allow mount information, including information about the topology tree to
be queried with the fsinfo() system call. Usage of AT_FSINFO_MOUNTID_PATH
allows overlapping mounts to be queried.
To this end, four fsinfo() attributes are provided:
(1) FSINFO_ATTR_MOUNT_INFO.
This is a structure providing information about a mount, including:
- Mounted superblock ID.
- Mount ID (as AT_FSINFO_MOUNTID_PATH).
- Parent mount ID.
- Mount attributes (eg. R/O, NOEXEC).
- Number of change notifications generated.
Note that the parent mount ID is overridden to the ID of the queried
mount if the parent lies outside of the chroot or dfd tree.
(2) FSINFO_ATTR_MOUNT_DEVNAME.
This a string providing the device name associated with the mount.
Note that the device name may be a path that lies outside of the root.
(3) FSINFO_ATTR_MOUNT_CHILDREN.
This produces an array of structures, one for each child and capped
with one for the argument mount (checked after listing all the
children). Each element contains the mount ID and the notification
counter of the respective mount object.
(4) FSINFO_ATTR_MOUNT_SUBMOUNT.
This is a 1D array of strings, indexed with struct fsinfo_params::Nth.
Each string is the relative pathname of the corresponding child
returned by FSINFO_ATTR_MOUNT_CHILD.
FSINFO_ATTR_MOUNT_CHILD -> FSINFO_ATTR_MOUNT_CHILDREN
Note that paths in the mount at the base of the tree (whether that be
dfd or chroot) are relative to the base of the tree, not the root
directory of that mount.
Signed-off-by: David Howells<dhowells@xxxxxxxxxx>
---
fs/d_path.c | 2
fs/fsinfo.c | 9 ++
fs/internal.h | 9 ++
fs/namespace.c | 175 +++++++++++++++++++++++++++++++++++++++++++
include/uapi/linux/fsinfo.h | 28 +++++++
samples/vfs/test-fsinfo.c | 47 +++++++++++-
6 files changed, 266 insertions(+), 4 deletions(-)
+/*
+ * Information struct for fsinfo(FSINFO_ATTR_MOUNT_INFO).
+ */
+struct fsinfo_mount_info {
+ __u64 f_sb_id; /* Superblock ID */
+ __u32 mnt_id; /* Mount identifier (use with AT_FSINFO_MOUNTID_PATH) */
+ __u32 parent_id; /* Parent mount identifier */
+ __u32 group_id; /* Mount group ID */
+ __u32 master_id; /* Slave master group ID */
+ __u32 from_id; /* Slave propogated from ID */
propogated -> propagated
+ __u32 attr; /* MOUNT_ATTR_* flags */
+ __u32 notify_counter; /* Number of notifications generated. */
+ __u32 __reserved[1];
+};
+
+/*
+ * Information struct element for fsinfo(FSINFO_ATTR_MOUNT_CHILDREN).
+ * - An extra element is placed on the end representing the parent mount.
+ */
+struct fsinfo_mount_child {
+ __u32 mnt_id; /* Mount identifier (use with AT_FSINFO_MOUNTID_PATH) */
+ __u32 notify_counter; /* Number of notifications generated on mount. */
+};
+
#endif /* _UAPI_LINUX_FSINFO_H */
