[PATCH v2] doc: Describe missing generic -blockdev options

[PATCH v2] doc: Describe missing generic -blockdev options

[Kevin Wolf]

We added more generic options after introducing -blockdev and forgot to
update the documentation (man page and --help output) accordingly. Do
that now.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 qemu-options.hx | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/qemu-options.hx b/qemu-options.hx
index 793d70ff93..2e6ba5ef1f 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -849,7 +849,8 @@ ETEXI
 DEF("blockdev", HAS_ARG, QEMU_OPTION_blockdev,
     "-blockdev [driver=]driver[,node-name=N][,discard=ignore|unmap]\n"
     "          [,cache.direct=on|off][,cache.no-flush=on|off]\n"
-    "          [,read-only=on|off][,detect-zeroes=on|off|unmap]\n"
+    "          [,read-only=on|off][,auto-read-only=on|off]\n"
+    "          [,force-share=on|off][,detect-zeroes=on|off|unmap]\n"
     "          [,driver specific parameters...]\n"
     "                configure a block backend\n", QEMU_ARCH_ALL)
 STEXI
@@ -885,6 +886,25 @@ name is not intended to be predictable and changes between QEMU invocations.
 For the top level, an explicit node name must be specified.
 @item read-only
 Open the node read-only. Guest write attempts will fail.
+
+Note that some block drivers support only read-only access, either generally or
+in certain configurations. In this case, the default value
+@option{read-only=off} does not work and the option must be specified
+explicitly.
+@item auto-read-only
+If @option{auto-read-only=on} is set, QEMU may fall back to read-only usage
+even when @option{read-only=off} is requested, or even switch between modes as
+needed, e.g. depending on whether the image file is writable or whether a
+writing user is attached to the node.
+@item force-share
+Override the image locking system of QEMU by forcing the node to utilize
+weaker shared access for permissions where it would normally request exclusive
+access.  When there is the potential for multiple instances to have the same
+file open (whether this invocation of qemu is the first or the second
+instance), both instances must permit shared access for the second instance to
+succeed at opening the file.
+
+Enabling @option{force-share=on} requires @option{read-only=on}.
 @item cache.direct
 The host page cache can be avoided with @option{cache.direct=on}. This will
 attempt to do disk IO directly to the guest's memory. QEMU may still perform an
-- 
2.20.1

Re: [PATCH v2] doc: Describe missing generic -blockdev options

[Peter Maydell]

On Fri, 18 Oct 2019 at 13:02, Kevin Wolf <kwolf@redhat.com> wrote:
>
> We added more generic options after introducing -blockdev and forgot to
> update the documentation (man page and --help output) accordingly. Do
> that now.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  qemu-options.hx | 22 +++++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 793d70ff93..2e6ba5ef1f 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -849,7 +849,8 @@ ETEXI
>  DEF("blockdev", HAS_ARG, QEMU_OPTION_blockdev,
>      "-blockdev [driver=]driver[,node-name=N][,discard=ignore|unmap]\n"
>      "          [,cache.direct=on|off][,cache.no-flush=on|off]\n"
> -    "          [,read-only=on|off][,detect-zeroes=on|off|unmap]\n"
> +    "          [,read-only=on|off][,auto-read-only=on|off]\n"
> +    "          [,force-share=on|off][,detect-zeroes=on|off|unmap]\n"
>      "          [,driver specific parameters...]\n"
>      "                configure a block backend\n", QEMU_ARCH_ALL)
>  STEXI
> @@ -885,6 +886,25 @@ name is not intended to be predictable and changes between QEMU invocations.
>  For the top level, an explicit node name must be specified.
>  @item read-only
>  Open the node read-only. Guest write attempts will fail.
> +
> +Note that some block drivers support only read-only access, either generally or
> +in certain configurations. In this case, the default value
> +@option{read-only=off} does not work and the option must be specified
> +explicitly.
> +@item auto-read-only
> +If @option{auto-read-only=on} is set, QEMU may fall back to read-only usage
> +even when @option{read-only=off} is requested, or even switch between modes as
> +needed, e.g. depending on whether the image file is writable or whether a
> +writing user is attached to the node.
> +@item force-share
> +Override the image locking system of QEMU by forcing the node to utilize
> +weaker shared access for permissions where it would normally request exclusive
> +access.  When there is the potential for multiple instances to have the same
> +file open (whether this invocation of qemu is the first or the second

"QEMU" should be all-upper-case.

> +instance), both instances must permit shared access for the second instance to
> +succeed at opening the file.
> +
> +Enabling @option{force-share=on} requires @option{read-only=on}.
>  @item cache.direct
>  The host page cache can be avoided with @option{cache.direct=on}. This will
>  attempt to do disk IO directly to the guest's memory. QEMU may still perform an
> --
> 2.20.1

Otherwise
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM