qemu-char: Saner naming of memchar stuff & doc fixes

New device, has never been released, so we can still improve things
without worrying about compatibility.

Naming is a mess.  The code calls the device driver CirMemCharDriver,
the public API calls it "memory", "memchardev", or "memchar", and the
special commands are named like "memchar-FOO".  "memory" is a
particularly unfortunate choice, because there's another character
device driver called MemoryDriver.  Moreover, the device's distinctive
property is that it's a ring buffer, not that's in memory.  Therefore:

* Rename CirMemCharDriver to RingBufCharDriver, and call the thing a
  "ringbuf" in the API.

* Rename QMP and HMP commands from memchar-FOO to ringbuf-FOO.

* Rename device parameter from maxcapacity to size (simple words are
  good for you).

* Clearly mark the parameter as optional in documentation.

* Fix error reporting so that chardev-add reports to current monitor,
  not stderr.

* Replace cirmem in C identifiers by ringbuf.

* Rework documentation.  Document the impact of our crappy UTF-8
  handling on reading.

* QMP examples that even work.

I could split this up into multiple commits, but they'd change the
same documentation lines multiple times.  Not worth it.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 29 insertions, 18 deletions

diff --git a/qapi-schema.json b/qapi-schema.json
index 6f6379151f..736f881b75 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -329,9 +329,9 @@
 #
 # An enumeration of data format.
 #
-# @utf8: The data format is 'utf8'.
+# @utf8: Data is a UTF-8 string (RFC 3629)
 #
-# @base64: The data format is 'base64'.
+# @base64: Data is Base64 encoded binary (RFC 3548)
 #
 # Since: 1.4
 ##
@@ -339,44 +339,55 @@
   'data': [ 'utf8', 'base64' ] }
 
 ##
-# @memchar-write:
+# @ringbuf-write:
 #
-# Provide writing interface for memchardev. Write data to char
-# device 'memory'.
+# Write to a ring buffer character device.
 #
-# @device: the name of the memory char device.
+# @device: the ring buffer character device name
 #
-# @data: the source data write to memchar.
+# @data: data to write
 #
-# @format: #optional the format of the data write to chardev 'memory',
-#          by default is 'utf8'.
+# @format: #optional data encoding (default 'utf8').
+#          - base64: data must be base64 encoded text.  Its binary
+#            decoding gets written.
+#            Bug: invalid base64 is currently not rejected.
+#            Whitespace *is* invalid.
+#          - utf8: data's UTF-8 encoding is written
+#          - data itself is always Unicode regardless of format, like
+#            any other string.
 #
 # Returns: Nothing on success
 #
 # Since: 1.4
 ##
-{ 'command': 'memchar-write',
+{ 'command': 'ringbuf-write',
   'data': {'device': 'str', 'data': 'str',
            '*format': 'DataFormat'} }
 
 ##
-# @memchar-read:
+# @ringbuf-read:
 #
-# Provide read interface for memchardev. Read from the char
-# device 'memory' and return the data.
+# Read from a ring buffer character device.
 #
-# @device: the name of the memory char device.
+# @device: the ring buffer character device name
 #
-# @size: the size to read in bytes.
+# @size: how many bytes to read at most
 #
-# @format: #optional the format of the data want to read from
-#          memchardev, by default is 'utf8'.
+# @format: #optional data encoding (default 'utf8').
+#          - base64: the data read is returned in base64 encoding.
+#          - utf8: the data read is interpreted as UTF-8.
+#            Bug: can screw up when the buffer contains invalid UTF-8
+#            sequences, NUL characters, after the ring buffer lost
+#            data, and when reading stops because the size limit is
+#            reached.
+#          - The return value is always Unicode regardless of format,
+#            like any other string.
 #
 # Returns: data read from the device
 #
 # Since: 1.4
 ##
-{ 'command': 'memchar-read',
+{ 'command': 'ringbuf-read',
   'data': {'device': 'str', 'size': 'int', '*format': 'DataFormat'},
   'returns': 'str' }