tools/virtiofsd: xattr name mappings: Simple 'map'

The mapping rule system implemented in the last few patches is
extremely flexible, but not easy to use.  Add a simple
'map' type as a sprinkling of sugar to make it easy.

e.g.

  -o xattrmap=":map::user.virtiofs.:"

would be sufficient to prefix all xattr's
or

  -o xattrmap=":map:trusted.:user.virtiofs.:"

would just prefix 'trusted.' xattr's and leave
everything else alone.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20201023165812.36028-6-dgilbert@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/docs/tools/virtiofsd.rst b/docs/tools/virtiofsd.rst
index d80c078d80..34a9e40146 100644
--- a/docs/tools/virtiofsd.rst
+++ b/docs/tools/virtiofsd.rst
@@ -147,6 +147,7 @@ Each rule consists of a number of fields separated with a separator that is the
 first non-white space character in the rule.  This separator must then be used
 for the whole rule.
 White space may be added before and after each rule.
+
 Using ':' as the separator a rule is of the form:
 
 ``:type:scope:key:prepend:``
@@ -219,6 +220,14 @@ e.g.:
 
   would hide 'security.' xattr's in listxattr from the server.
 
+A simpler 'map' type provides a shorter syntax for the common case:
+
+``:map:key:prepend:``
+
+The 'map' type adds a number of separate rules to add **prepend** as a prefix
+to the matched **key** (or all attributes if **key** is empty).
+There may be at most one 'map' rule and it must be the last rule in the set.
+
 xattr-mapping Examples
 ----------------------
 
@@ -234,6 +243,11 @@ the first rule prefixes and strips 'user.virtiofs.',
 the second rule hides any non-prefixed attributes that
 the host set.
 
+This is equivalent to the 'map' rule:
+
+::
+-o xattrmap=":map::user.virtiofs.:"
+
 2) Prefix 'trusted.' attributes, allow others through
 
 ::
@@ -256,6 +270,11 @@ the 'user.virtiofs.' path directly.
 Finally, the fourth rule lets all remaining attributes
 through.
 
+This is equivalent to the 'map' rule:
+
+::
+-o xattrmap="/map/trusted./user.virtiofs./"
+
 3) Hide 'security.' attributes, and allow everything else
 
 ::