Re: [PATCH] tools: specifically enable VirtFS in Linux QEMU builds

[George Dunlap <george.dunlap@citrix.com>]

On 09/06/2018 01:06 PM, Paul Durrant wrote:
> 9pfs support has been a documented feature since Xen 4.9, but QEMU will
> not be built with backend support unless libcap and libattr dev packages
> are installed.
> 
> This patch modifies the README to call out those packages as pre-requisites
> for Linux builds and specifically enables VirtFS in the configure line
> for QEMU so that an error message is displayed if they are missing.
> 
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> ---
> Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> Cc: George Dunlap <George.Dunlap@eu.citrix.com>
> Cc: Ian Jackson <ian.jackson@eu.citrix.com>
> Cc: Jan Beulich <jbeulich@suse.com>
> Cc: Julien Grall <julien.grall@arm.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: Tim Deegan <tim@xen.org>
> Cc: Wei Liu <wei.liu2@citrix.com>
> ---
>  README         |  2 ++
>  tools/Makefile | 11 +++++++++++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/README b/README
> index 4b95b21c7b..1a4e4b2c1b 100644
> --- a/README
> +++ b/README
> @@ -56,6 +56,8 @@ provided by your OS distributor:
>        greater.
>      * Development install of GLib v2.0 (e.g. libglib2.0-dev)
>      * Development install of Pixman (e.g. libpixman-1-dev)
> +    * Development install of libcap (e.g. libcap-dev) [Linux only]
> +    * Development install of libattr (e.g. libattr1-dev) [Linux only]
>      * pkg-config
>      * bridge-utils package (/sbin/brctl)
>      * iproute package (/sbin/ip)
> diff --git a/tools/Makefile b/tools/Makefile
> index 67977ad850..e74efb8a6e 100644
> --- a/tools/Makefile
> +++ b/tools/Makefile
> @@ -216,6 +216,11 @@ else
>  QEMU_XEN_ENABLE_DEBUG :=
>  endif
>  
> +#
> +# 9pfs support is a documented feature but it depends on a QEMU with
> +# VirtFS enabled. However VirtFS is a Linux-only option so only enable
> +# it for Linux builds.
> +#
>  subdir-all-qemu-xen-dir: qemu-xen-dir-find
>  	unset MAKELEVEL; \
>  	if test -d $(QEMU_UPSTREAM_LOC) ; then \
> @@ -232,10 +237,16 @@ subdir-all-qemu-xen-dir: qemu-xen-dir-find
>  	else \
>  		enable_trace_backend='' ; \
>  	fi ; \
> +	if [ "$(CONFIG_Linux)" = "y" ]; then \
> +		enable_virtfs='--enable-virtfs' ; \
> +	else \
> +		enable_virtfs='' ; \
> +	fi ; \

9pfs is still a reasonably "niche" feature; I don't think we want to
force people to enable it if they don't expect to use it.

Is it the case that if we have libcap and libattr, that qemu will enable
9pfs automatically?  If so we should just document that.

Another option would be to have "--enable-9pfs" option in the tools
configure, which would then pass this on to qemu (and thus fail if the
requisite librares aren't present), but I'm not sure if having a load of
"--enable-*" at the top level is really what we want for this.

 -George

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