qemu-options: Clarify handling of commas in options parameters

Provide explicit guidance on dealing with option parameters as arbitrary
strings containing commas, such as in "file=my,file" and "string=a,b". The
updated documentation emphasizes the need to double commas when they
appear within such parameters.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1839
Signed-off-by: Yihuan Pan <xun794@gmail.com>
Message-ID: <20231213141706.629833-2-xun794@gmail.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

docs/system/invocation.rst

@@ -10,6 +10,11 @@ Invocation
 disk_image is a raw hard disk image for IDE hard disk 0. Some targets do
 not need a disk image.
 
+When dealing with options parameters as arbitrary strings containing
+commas, such as in "file=my,file" and "string=a,b", it's necessary to
+double the commas. For instance,"-fw_cfg name=z,string=a,,b" will be
+parsed as "-fw_cfg name=z,string=a,b".
+
 .. hxtool-doc:: qemu-options.hx
 
 Device URL Syntax

docs/system/qemu-manpage.rst

@@ -31,6 +31,11 @@ Options
 disk_image is a raw hard disk image for IDE hard disk 0. Some targets do
 not need a disk image.
 
+When dealing with options parameters as arbitrary strings containing
+commas, such as in "file=my,file" and "string=a,b", it's necessary to
+double the commas. For instance,"-fw_cfg name=z,string=a,,b" will be
+parsed as "-fw_cfg name=z,string=a,b".
+
 .. hxtool-doc:: qemu-options.hx
 
 .. include:: keys.rst.inc

qemu-options.hx

@@ -4086,9 +4086,13 @@ DEF("fw_cfg", HAS_ARG, QEMU_OPTION_fwcfg,
 SRST
 ``-fw_cfg [name=]name,file=file``
     Add named fw\_cfg entry with contents from file file.
+    If the filename contains comma, you must double it (for instance,
+    "file=my,,file" to use file "my,file").
 
 ``-fw_cfg [name=]name,string=str``
     Add named fw\_cfg entry with contents from string str.
+    If the string contains comma, you must double it (for instance,
+    "string=my,,string" to use file "my,string").
 
     The terminating NUL character of the contents of str will not be
     included as part of the fw\_cfg item data. To insert contents with