fw_cfg: Adopt /opt/RFQDN convention

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Merge remote-tracking branch 'remotes/armbru/tags/pull-fw_cfg-2016-04-19' into staging

fw_cfg: Adopt /opt/RFQDN convention

# gpg: Signature made Tue 19 Apr 2016 15:14:20 BST using RSA key ID EB918653
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>"
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>"

* remotes/armbru/tags/pull-fw_cfg-2016-04-19:
  fw_cfg: Adopt /opt/RFQDN convention

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

docs/specs/fw_cfg.txt

@@ -210,29 +210,27 @@ the following syntax:
 
     -fw_cfg [name=]<item_name>,file=<path>
 
-where <item_name> is the fw_cfg item name, and <path> is the location
-on the host file system of a file containing the data to be inserted.
-
-Small enough items may be provided directly as strings on the command
-line, using the syntax:
+Or
 
     -fw_cfg [name=]<item_name>,string=<string>
 
-The terminating NUL character of the content <string> will NOT be
-included as part of the fw_cfg item data, which is consistent with
-the absence of a NUL terminator for items inserted via the file option.
+See QEMU man page for more documentation.
 
-Both <item_name> and, if applicable, the content <string> are passed
-through by QEMU without any interpretation, expansion, or further
-processing. Any such processing (potentially performed e.g., by the shell)
-is outside of QEMU's responsibility; as such, using plain ASCII characters
-is recommended.
+Using item_name with plain ASCII characters only is recommended.
 
-NOTE: Users *SHOULD* choose item names beginning with the prefix "opt/"
-when using the "-fw_cfg" command line option, to avoid conflicting with
-item names used internally by QEMU. For instance:
+Item names beginning with "opt/" are reserved for users.  QEMU will
+never create entries with such names unless explicitly ordered by the
+user.
 
-    -fw_cfg name=opt/my_item_name,file=./my_blob.bin
+To avoid clashes among different users, it is strongly recommended
+that you use names beginning with opt/RFQDN/, where RFQDN is a reverse
+fully qualified domain name you control.  For instance, if SeaBIOS
+wanted to define additional names, the prefix "opt/org.seabios/" would
+be appropriate.
 
-Similarly, QEMU developers *SHOULD NOT* use item names prefixed with
-"opt/" when inserting items programmatically, e.g. via fw_cfg_add_file().
+For historical reasons, "opt/ovmf/" is reserved for OVMF firmware.
+
+Prefix "opt/org.qemu/" is reserved for QEMU itself.
+
+Use of names not beginning with "opt/" is potentially dangerous and
+entirely unsupported.  QEMU will warn if you try.

qemu-options.hx

@@ -2864,18 +2864,32 @@ ETEXI
 
 DEF("fw_cfg", HAS_ARG, QEMU_OPTION_fwcfg,
     "-fw_cfg [name=]<name>,file=<file>\n"
-    "                add named fw_cfg entry from file\n"
+    "                add named fw_cfg entry with contents from file\n"
     "-fw_cfg [name=]<name>,string=<str>\n"
-    "                add named fw_cfg entry from string\n",
+    "                add named fw_cfg entry with contents from string\n",
     QEMU_ARCH_ALL)
 STEXI
+
 @item -fw_cfg [name=]@var{name},file=@var{file}
 @findex -fw_cfg
-Add named fw_cfg entry from file. @var{name} determines the name of
-the entry in the fw_cfg file directory exposed to the guest.
+Add named fw_cfg entry with contents from file @var{file}.
 
 @item -fw_cfg [name=]@var{name},string=@var{str}
-Add named fw_cfg entry from string.
+Add named fw_cfg entry with contents from string @var{str}.
+
+The terminating NUL character of the contents of @var{str} will not be
+included as part of the fw_cfg item data. To insert contents with
+embedded NUL characters, you have to use the @var{file} parameter.
+
+The fw_cfg entries are passed by QEMU through to the guest.
+
+Example:
+@example
+    -fw_cfg name=opt/com.mycompany/blob,file=./my_blob.bin
+@end example
+creates an fw_cfg entry named opt/com.mycompany/blob with contents
+from ./my_blob.bin.
+
 ETEXI
 
 DEF("serial", HAS_ARG, QEMU_OPTION_serial, \