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-rw-r--r--docs/specs/fw_cfg.txt13
1 files changed, 12 insertions, 1 deletions
diff --git a/docs/specs/fw_cfg.txt b/docs/specs/fw_cfg.txt
index 8f1ebc66fa..3e6d586f66 100644
--- a/docs/specs/fw_cfg.txt
+++ b/docs/specs/fw_cfg.txt
@@ -219,7 +219,7 @@ To check the result, read the "control" field:
= Externally Provided Items =
-As of v2.4, "file" fw_cfg items (i.e., items with selector keys above
+Since v2.4, "file" fw_cfg items (i.e., items with selector keys above
FW_CFG_FILE_FIRST, and with a corresponding entry in the fw_cfg file
directory structure) may be inserted via the QEMU command line, using
the following syntax:
@@ -230,6 +230,13 @@ Or
-fw_cfg [name=]<item_name>,string=<string>
+Since v5.1, QEMU allows some objects to generate fw_cfg-specific content,
+the content is then associated with a "file" item using the 'gen_id' option
+in the command line, using the following syntax:
+
+ -object <generator-type>,id=<generated_id>,[generator-specific-options] \
+ -fw_cfg [name=]<item_name>,gen_id=<generated_id>
+
See QEMU man page for more documentation.
Using item_name with plain ASCII characters only is recommended.
@@ -251,4 +258,8 @@ 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.
+Use of names not beginning with "opt/" is tolerated with 'gen_id' (that
+is, the warning is suppressed), but you must know exactly what you're
+doing.
+
All externally provided fw_cfg items are read-only to the guest.