Update the fsinfo documentation to mention mount and sb watches.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---
Documentation/filesystems/fsinfo.rst | 38 +++++++++++++++++++++++++++++++++-
1 file changed, 37 insertions(+), 1 deletion(-)
diff --git a/Documentation/filesystems/fsinfo.rst b/Documentation/filesystems/fsinfo.rst
index 86c187a46396..ef79582b991d 100644
--- a/Documentation/filesystems/fsinfo.rst
+++ b/Documentation/filesystems/fsinfo.rst
@@ -7,7 +7,8 @@ security information beyond what stat(), statx() and statfs() can query. It
does not require a file to be opened as does ioctl().
fsinfo() may be called on a path, an open file descriptor, a filesystem-context
-file descriptor as allocated by fsopen() or fspick().
+file descriptor as allocated by fsopen() or fspick() or a mount ID (allowing
+for mounts concealed by overmounts to be accessed).
The fsinfo() system call needs to be configured on by enabling:
@@ -235,6 +236,10 @@ To summarise the attributes that are defined::
FSINFO_ATTR_SERVER_NAME N × string
FSINFO_ATTR_SERVER_ADDRESS N × M × struct
FSINFO_ATTR_AFS_CELL_NAME string
+ FSINFO_ATTR_MOUNT_INFO struct
+ FSINFO_ATTR_MOUNT_DEVNAME string
+ FSINFO_ATTR_MOUNT_CHILDREN array
+ FSINFO_ATTR_MOUNT_SUBMOUNT N × string
Attribute Catalogue
@@ -386,6 +391,37 @@ before any superblock is attached:
before noting any other parameters.
+Then there are attributes that convey information about the mount topology:
+
+ * ``FSINFO_ATTR_MOUNT_INFO``
+
+ This struct-type attribute conveys information about a mount topology node
+ rather than a superblock. This includes the ID of the superblock mounted
+ there and the ID of the mount node, its parent, group, master and
+ propagation source. It also contains the attribute flags for the mount and
+ a change counter so that it can be quickly determined if that node changed.
+
+ * ``FSINFO_ATTR_MOUNT_DEVNAME``
+
+ This string-type attribute returns the "device name" that was supplied when
+ the mount object was created.
+
+ * ``FSINFO_ATTR_MOUNT_CHILDREN``
+
+ This is an array-type attribute that conveys a set of structs, each of
+ which indicates the mount ID of a child and the change counter for that
+ child. The kernel also tags an extra element on the end that indicates the
+ ID and change counter of the queried object. This allows a conflicting
+ change to be quickly detected by comparing the before and after counters.
+
+ * ``FSINFO_ATTR_MOUNT_SUBMOUNT``
+
+ This is a string-type attribute that conveys the pathname of the Nth
+ mountpoint under the target mount, relative to the mount root or the
+ chroot, whichever is closer. These correspond on a 1:1 basis with the
+ elements in the FSINFO_ATTR_MOUNT_CHILDREN list.
+
+
Then there are filesystem-specific attributes.
* ``FSINFO_ATTR_SERVER_NAME``
