s390/zcrypt: multiple zcrypt device nodes support

s390/zcrypt: multiple zcrypt device nodes support

This patch is an extension to the zcrypt device driver to provide,
support and maintain multiple zcrypt device nodes. The individual
zcrypt device nodes can be restricted in terms of crypto cards,
domains and available ioctls. Such a device node can be used as a
base for container solutions like docker to control and restrict
the access to crypto resources.

The handling is done with a new sysfs subdir /sys/class/zcrypt.
Echoing a name (or an empty sting) into the attribute "create" creates
a new zcrypt device node. In /sys/class/zcrypt a new link will appear
which points to the sysfs device tree of this new device. The
attribute files "ioctlmask", "apmask" and "aqmask" in this directory
are used to customize this new zcrypt device node instance. Finally
the zcrypt device node can be destroyed by echoing the name into
/sys/class/zcrypt/destroy. The internal structs holding the device
info are reference counted - so a destroy will not hard remove a
device but only marks it as removable when the reference counter drops
to zero.

The mask values are bitmaps in big endian order starting with bit 0.
So adapter number 0 is the leftmost bit, mask is 0x8000...  The sysfs
attributes accept 2 different formats:
* Absolute hex string starting with 0x like "0x12345678" does set
  the mask starting from left to right. If the given string is shorter
  than the mask it is padded with 0s on the right. If the string is
  longer than the mask an error comes back (EINVAL).
* Relative format - a concatenation (done with ',') of the
  terms +<bitnr>[-<bitnr>] or -<bitnr>[-<bitnr>]. <bitnr> may be any
  valid number (hex, decimal or octal) in the range 0...255. Here are
  some examples:
    "+0-15,+32,-128,-0xFF"
    "-0-255,+1-16,+0x128"
    "+1,+2,+3,+4,-5,-7-10"

A simple usage examples:

  # create new zcrypt device 'my_zcrypt':
  echo "my_zcrypt" >/sys/class/zcrypt/create
  # go into the device dir of this new device
  echo "my_zcrypt" >create
  cd my_zcrypt/
  ls -l
  total 0
  -rw-r--r-- 1 root root 4096 Jul 20 15:23 apmask
  -rw-r--r-- 1 root root 4096 Jul 20 15:23 aqmask
  -r--r--r-- 1 root root 4096 Jul 20 15:23 dev
  -rw-r--r-- 1 root root 4096 Jul 20 15:23 ioctlmask
  lrwxrwxrwx 1 root root    0 Jul 20 15:23 subsystem -> ../../../../class/zcrypt
  ...
  # customize this zcrypt node clone
  # enable only adapter 0 and 2
  echo "0xa0" >apmask
  # enable only domain 6
  echo "+6" >aqmask
  # enable all 256 ioctls
  echo "+0-255" >ioctls
  # now the /dev/my_zcrypt may be used
  # finally destroy it
  echo "my_zcrypt" >/sys/class/zcrypt/destroy

Please note that a very similar 'filtering behavior' also applies to
the parent z90crypt device. The two mask attributes apmask and aqmask
in /sys/bus/ap act the very same for the z90crypt device node. However
the implementation here is totally different as the ap bus acts on
bind/unbind of queue devices and associated drivers but the effect is
still the same. So there are two filters active for each additional
zcrypt device node: The adapter/domain needs to be enabled on the ap
bus level and it needs to be active on the zcrypt device node level.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>