Am 10.07.2026 um 11:36 hat Thomas Huth geschrieben:
> From: Thomas Huth <[email protected]>
>
> Other command line options like "-chardev", "-netdev" or "-device"
> already present the user with a list of available parameters, but
> when running "-blockdev help", there is currently only an error
> message. There is already the possibility to run "-drive format=help",
> but it does not seem to be documented, so this is not very useful
> for the average user. Let's improve this situation by providing
> the same list of available drivers when running QEMU with
> "-blockdev help".
>
> Signed-off-by: Thomas Huth <[email protected]>
Seems like a good idea to print at least some minimal help there.
However, I find the list from -drive format=help quite hard to read, and
repeating the same list twice for read-write and read-only doesn't help
either.
I don't expect we can change -drive because I seem to remember that
management tools look at it, but can we make -blockdev help more
consistent with the other examples you mention? Something like this:
Available blockdev drivers:
blkdebug
blklogwrites (read-only)
blkreplay
...
Ideally, I'd also love to have a way to show all the options a specific
driver offers, but that probably won't happen before Markus QAPIfies the
CLI. :-)
> include/block/block-common.h | 1 +
> blockdev.c | 15 ++++++++++-----
> system/vl.c | 7 +++++--
> 3 files changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/include/block/block-common.h b/include/block/block-common.h
> index 895ea175413..010c4425dcf 100644
> --- a/include/block/block-common.h
> +++ b/include/block/block-common.h
> @@ -583,5 +583,6 @@ char *path_combine(const char *base_path, const char
> *filename);
> char *bdrv_get_full_backing_filename_from_filename(const char *backed,
> const char *backing,
> Error **errp);
> +void blockdev_show_help(void);
>
> #endif /* BLOCK_COMMON_H */
> diff --git a/blockdev.c b/blockdev.c
> index 6e86c6262f9..3d179939205 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -475,6 +475,15 @@ static OnOffAuto account_get_opt(QemuOpts *opts, const
> char *name)
> return ON_OFF_AUTO_OFF;
> }
>
> +void blockdev_show_help(void)
> +{
> + qemu_printf("Supported formats:");
We should definitely talk about "drivers" rather than "formats" with
-blockdev. The help in -drive was added in QEMU 0.10 when "formats" was
actually still accurate, but it hasn't been for a long time.
> + bdrv_iterate_format(bdrv_format_print, NULL, false);
> + qemu_printf("\nSupported formats (read-only):");
> + bdrv_iterate_format(bdrv_format_print, NULL, true);
> + qemu_printf("\n");
> +}
> +
> /* Takes the ownership of bs_opts */
> static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,
> Error **errp)
> @@ -541,11 +550,7 @@ static BlockBackend *blockdev_init(const char *file,
> QDict *bs_opts,
>
> if ((buf = qemu_opt_get(opts, "format")) != NULL) {
> if (is_help_option(buf)) {
> - qemu_printf("Supported formats:");
> - bdrv_iterate_format(bdrv_format_print, NULL, false);
> - qemu_printf("\nSupported formats (read-only):");
> - bdrv_iterate_format(bdrv_format_print, NULL, true);
> - qemu_printf("\n");
> + blockdev_show_help();
> goto early_err;
> }
>
> diff --git a/system/vl.c b/system/vl.c
> index 061cbdf860b..40c0593154a 100644
> --- a/system/vl.c
> +++ b/system/vl.c
> @@ -2961,7 +2961,10 @@ void qemu_init(int argc, char **argv)
> HD_OPTS);
> break;
> case QEMU_OPTION_blockdev:
> - {
> + if (is_help_option(optarg)) {
> + blockdev_show_help();
> + exit(EXIT_SUCCESS);
> + } else {
> Visitor *v;
> BlockdevOptionsQueueEntry *bdo;
>
> @@ -2974,8 +2977,8 @@ void qemu_init(int argc, char **argv)
> visit_free(v);
> loc_save(&bdo->loc);
> QSIMPLEQ_INSERT_TAIL(&bdo_queue, bdo, entry);
> - break;
> }
> + break;
> case QEMU_OPTION_drive:
> if (!qemu_opts_parse_noisily(qemu_find_opts("drive"),
> optarg, false)) {
> --
> 2.55.0
Kevin
