notebook: update genfscon documentation

Partial paths can be used generally for virtual kernel filesystems, e.g.
cgroup2, securityfs, selinuxfs, and not just for the proc filesystem.

The genfscon statement supports an optional filetype specifier.

Signed-off-by: Christian Göttsche <[email protected]>

src/file_labeling_statements.md

@@ -184,16 +184,17 @@ The *genfscon* statement is used to allocate a security context to
 filesystems that cannot support any of the other file labeling
 statements (*fs_use_xattr*, *fs_use_task* or *fs_use_trans*). Generally
 a filesystem would have a single default security context assigned by
-*genfscon* from the root (/) that would then be inherited by all files and
-directories on that filesystem. The exception to this is the */proc*
-filesystem, where directories can be labeled with a specific security
-context (as shown in the examples). Note that there is no terminating
-semi-colon on this statement.
+*genfscon* from the root (*/*) that would then be inherited by all files and
+directories on that filesystem. File entries can be, if supported by the
+underlying filesystem, labeled with a specific security context (as shown in
+the examples), which is useful for pseudo filesystems exporting kernel state
+(e.g. *proc*, *sysfs*, *cgroup2*, *securityfs*, *selinuxfs*).
+Note that there is no terminating semi-colon on this statement.
 
 **The statement definition is:**
 
 ```
-genfscon fs_name partial_path fs_context
+genfscon fs_name partial_path [filetype_specifier] fs_context
 ```
 
 **Where:**
@@ -208,8 +209,23 @@ The filesystem name.
 
 *partial_path*
 
-If *fs_name* is *proc*, then the partial path (see the examples). For all other
-types, this must be */*.
+If *fs_name* is a virtual kernel filesystem, then the partial path (see the
+examples). For all other types, this must be */*.
+
+*filetype_specifier*
+
+Optional filetype specifier to apply the context only to a specific file type.
+Valid specifiers are:
+
+- *-b* block device
+- *-c* character device
+- *-d* directory
+- *-p* named pipe
+- *-l* symbolic link
+- *-s* socket
+- *--* regular file
+
+If omitted the context applies to all file types.
 
 *fs_context*
 
@@ -241,14 +257,20 @@ genfscon selinuxfs / system_u:object_r:security_t:s0
 ```
 
 ```
-# The following show some example /proc entries. Note that the
-# /kmsg has the highest sensitivity level assigned (s15) because
-# it is a trusted process.
+# The following examples show pseudo kernel filesystem entries. Note that
+# the /kmsg has the highest sensitivity level assigned (s15) because
+# it is a file containing possibly sensitive information.
+
+genfscon cgroup2 "/user.slice" -d system_u:object_r:cgroup_user_slice_t:s0
 
 genfscon proc / system_u:object_r:proc_t:s0
 genfscon proc /sysvipc system_u:object_r:proc_t:s0
 genfscon proc /fs/openafs system_u:object_r:proc_afs_t:s0
 genfscon proc /kmsg system_u:object_r:proc_kmsg_t:s15:c0.c255
+
+genfscon selinuxfs /booleans/secure_mode_policyload -- system_u:object_r:secure_mode_policyload_boolean_t:s0
+
+genfscon sysfs /devices/system/cpu/online -- system_u:object_r:cpu_online_sysfs_t:s0
 ```
 
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