[PATCH] docs: Discourage users from using fwcfg

[Michal Privoznik]

Even though this was brought up in upstream discussion [1] it
missed my patches: users should prefer <oemStrings/> over fwcfg.
The reason is that fwcfg is considered somewhat internal to QEMU
and it has limited number of slots and neither of these applies
to <oemStrings/>.

While I'm at it, I'm fixing the example too (because it contains
incorrect element name) and clarifying sysfs/ exposure.

1: https://www.redhat.com/archives/libvir-list/2020-May/msg00957.html

Reported-by: Laszlo Ersek <lersek at redhat.com>
Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 docs/formatdomain.rst | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index 1979dfb8d3..821ffe8d60 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -509,18 +509,22 @@ layout of sub-elements, with supported values of:
    Some hypervisors provide unified way to tweak how firmware configures itself,
    or may contain tables to be installed for the guest OS, for instance boot
    order, ACPI, SMBIOS, etc. It even allows users to define their own config
-   blobs. In case of QEMU, these then appear under domain's sysfs, under
+   blobs. In case of QEMU, these then appear under domain's sysfs (if the guest
+   kernel has FW_CFG_SYSFS config option enabled), under
    ``/sys/firmware/qemu_fw_cfg``. Note, that these values apply regardless the
    <smbios/> mode under <os/>. :since:`Since 6.5.0`
 
+   **Please note that because of limited number of data slots use of fwcfg is
+   strongly discouraged and <oemStrings/> should be used instead**.
+
    ::
 
-        <smbios type='fwcfg'>
+        <sysinfo type='fwcfg'>
           <entry name='opt/com.example/name'>example value</entry>
-          <entry name='opt/com.coreos/config' file='/tmp/provision.ign'/>
-        </smbios>
+          <entry name='opt/com.example/config' file='/tmp/provision.ign'/>
+        </sysinfo>
 
-   The ``smbios`` element can have multiple ``entry`` child elements. Each
+   The ``sysinfo`` element can have multiple ``entry`` child elements. Each
    element then has mandatory ``name`` attribute, which defines the name of the
    blob and must begin with ``"opt/"`` and to avoid clashing with other names is
    advised to be in form ``"opt/$RFQDN/$name"`` where ``$RFQDN`` is a reverse
-- 
2.26.2