[kvm-unit-tests PATCH v4 07/13] scripts: Add default arguments for kvmtool

[Andrew Jones]

On Wed, Jun 25, 2025 at 04:48:07PM +0100, Alexandru Elisei wrote:
> kvmtool, unless told otherwise, will do its best to make sure that a kernel
> successfully boots in a virtual machine. It does things like automatically
> creating a rootfs and adding extra parameters to the kernel command line.
> This is actively harmful to kvm-unit-tests, because some tests parse the
> kernel command line and they will fail if they encounter the options added
> by kvmtool.
> 
> Fortunately for us, kvmtool commit 5613ae26b998 ("Add --nodefaults command
> line argument") addded the --nodefaults kvmtool parameter which disables
> all the implicit virtual machine configuration that cannot be disabled by
> using other parameters, like modifying the kernel command line. So always
> use --nodefaults to allow a test to run.
> 
> kvmtool can also be too verbose when running a virtual machine, and this is
> controlled by several parameters. Add those to the default kvmtool command
> line to reduce this verbosity to a minimum.
> 
> Before:
> 
> $ vm run arm/selftest.flat --cpus 2 --mem 256 --params "setup smp=2 mem=256"
> Info: # lkvm run -k arm/selftest.flat -m 256 -c 2 --name guest-5035
> Unknown subtest
> 
> EXIT: STATUS=127
> Warning: KVM compatibility warning.
>     virtio-9p device was not detected.
>     While you have requested a virtio-9p device, the guest kernel did not initialize it.
>     Please make sure that the guest kernel was compiled with CONFIG_NET_9P_VIRTIO=y enabled in .config.
> Warning: KVM compatibility warning.
>     virtio-net device was not detected.
>     While you have requested a virtio-net device, the guest kernel did not initialize it.
>     Please make sure that the guest kernel was compiled with CONFIG_VIRTIO_NET=y enabled in .config.
> Info: KVM session ended normally.
> 
> After:
> 
> $ vm run arm/selftest.flat --nodefaults --network mode=none --loglevel=warning --cpus 2 --mem 256 --params "setup smp=2 mem=256"
> PASS: selftest: setup: smp: number of CPUs matches expectation
> INFO: selftest: setup: smp: found 2 CPUs
> PASS: selftest: setup: mem: memory size matches expectation
> INFO: selftest: setup: mem: found 256 MB
> SUMMARY: 2 tests
> 
> EXIT: STATUS=1
> 
> Note that KVMTOOL_DEFAULT_OPTS can be overwritten by an environment
> variable with the same name, but it's not documented in the help string for
> run_tests.sh. This has been done on purpose, since overwritting
> KVMTOOL_DEFAULT_OPTS should only be necessary for debugging or development
> purposes.
> 
> Reviewed-by: Andrew Jones <andrew.jones at linux.dev>
> Reviewed-by: Shaoqin Huang <shahuang at redhat.com>
> Signed-off-by: Alexandru Elisei <alexandru.elisei at arm.com>
> ---
> 
> Changes v3->v4:
> 
> * Use vmm_default_opts() instead of indexing into vmm_optname
> * Reworded the help test for --nodefaults as per Shaoqin's suggestion.
> 
>  scripts/common.bash |  6 +++---
>  scripts/vmm.bash    | 18 ++++++++++++++++++
>  2 files changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/scripts/common.bash b/scripts/common.bash
> index 7c1b89f1b3c2..d5d3101c8089 100644
> --- a/scripts/common.bash
> +++ b/scripts/common.bash
> @@ -37,7 +37,7 @@ function for_each_unittest()
>  			# -append as a kernel parameter instead of a command
>  			# line option.
>  			test_args=""
> -			opts=""
> +			opts="$(vmm_default_opts)"
>  			groups=""
>  			arch=""
>  			machine=""
> @@ -51,7 +51,7 @@ function for_each_unittest()
>  		elif [[ $line =~ ^test_args\ *=\ *(.*)$ ]]; then
>  			test_args="$(vmm_optname_args) ${BASH_REMATCH[1]}"
>  		elif [[ $line =~ ^$params_name\ *=\ *'"""'(.*)$ ]]; then
> -			opts=${BASH_REMATCH[1]}$'\n'
> +			opts="$(vmm_defaults_opts) ${BASH_REMATCH[1]}$'\n'"

Could be opts+=" ${BASH_REMATCH[1]}$'\n'", right?

>  			while read -r -u $fd; do
>  				#escape backslash newline, but not double backslash
>  				if [[ $opts =~ [^\\]*(\\*)$'\n'$ ]]; then
> @@ -67,7 +67,7 @@ function for_each_unittest()
>  				fi
>  			done
>  		elif [[ $line =~ ^$params_name\ *=\ *(.*)$ ]]; then
> -			opts=${BASH_REMATCH[1]}
> +			opts="$(vmm_default_opts) ${BASH_REMATCH[1]}"

Same comment.

Not a big deal either way, though, so my r-b stands.

Thanks,
drew

>  		elif [[ $line =~ ^groups\ *=\ *(.*)$ ]]; then
>  			groups=${BASH_REMATCH[1]}
>  		elif [[ $line =~ ^arch\ *=\ *(.*)$ ]]; then
> diff --git a/scripts/vmm.bash b/scripts/vmm.bash
> index 0dd3f971ecdf..368690d62473 100644
> --- a/scripts/vmm.bash
> +++ b/scripts/vmm.bash
> @@ -1,3 +1,14 @@
> +# The following parameters are enabled by default when running a test with
> +# kvmtool:
> +# --nodefaults: suppress VM configuration that cannot be disabled (like
> +#               modifying the supplied kernel command line). Otherwise tests
> +#               that use the command line will fail without this parameter.
> +# --network mode=none: do not create a network device. kvmtool tries to help the
> +#               user by automatically create one, and then prints a warning
> +#               when the VM terminates if the device hasn't been initialized.
> +# --loglevel=warning: reduce verbosity
> +: "${KVMTOOL_DEFAULT_OPTS:="--nodefaults --network mode=none --loglevel=warning"}"
> +
>  ##############################################################################
>  # qemu_fixup_return_code translates the ambiguous exit status in Table1 to that
>  # in Table2.  Table3 simply documents the complete status table.
> @@ -82,11 +93,13 @@ function kvmtool_fixup_return_code()
>  
>  declare -A vmm_optname=(
>  	[qemu,args]='-append'
> +	[qemu,default_opts]=''
>  	[qemu,fixup_return_code]=qemu_fixup_return_code
>  	[qemu,initrd]='-initrd'
>  	[qemu,nr_cpus]='-smp'
>  
>  	[kvmtool,args]='--params'
> +	[kvmtool,default_opts]="$KVMTOOL_DEFAULT_OPTS"
>  	[kvmtool,fixup_return_code]=kvmtool_fixup_return_code
>  	[kvmtool,initrd]='--initrd'
>  	[kvmtool,nr_cpus]='--cpus'
> @@ -97,6 +110,11 @@ function vmm_optname_args()
>  	echo ${vmm_optname[$(vmm_get_target),args]}
>  }
>  
> +function vmm_default_opts()
> +{
> +	echo ${vmm_optname[$(vmm_get_target),default_opts]}
> +}
> +
>  function vmm_fixup_return_code()
>  {
>  	${vmm_optname[$(vmm_get_target),fixup_return_code]} "$@"
> -- 
> 2.50.0
> 
> 
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