nvme/rc, md/001: check that nvme-cli supports json output format

When nvme-cli is built on a system without the json-c library, the nvme
command does not support the json output format. Consequently, the
"-o json" option, or in the long form "--output-format=json", of the
nvme command fails. It causes the helper function _nvme_connect_subsys()
to break. This leads to silent failures in many test cases in the nvme
test group as well as the test case md/001.

To inform blktests users this prerequisite, call the helper function
_have_nvme_cli_with_json_support(). As to the nvme test group, do the
check in group_requires() so that the check is done only once for all of
the test cases in the group. If the format is unsupported, the nvme test
group and the test case md/001 are skipped, and the reason to skip is
printed. This change makes the nvme command existence check in
_nvme_requires() redundant, then remove it.

Link: https://lore.kernel.org/linux-nvme/[email protected]/
Fixes: 444f0df ("nvme: check for controller device in _nvme_connect_subsys()")
Reported-by: Christoph Hellwig <[email protected]>
Reviewed-by: Chaitanya Kulkarni <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Daniel Wagner <[email protected]>
Signed-off-by: Shin'ichiro Kawasaki <[email protected]>

Author: kawasaki

tests/md/001

@@ -26,6 +26,7 @@ requires() {
 	_have_driver dm-mod
 	_have_driver raid1
 
+	_have_nvme_cli_with_json_support
 	_require_nvme_trtype tcp
 	_have_brd
 }

tests/nvme/rc

@@ -55,7 +55,6 @@ _set_nvmet_blkdev_type() {
 }
 
 _nvme_requires() {
-	_have_program nvme
 	_require_nvme_test_img_size 4m
 	case ${nvme_trtype} in
 	loop)
@@ -123,6 +122,7 @@ group_setup() {
 group_requires() {
 	_have_root
 	_NVMET_TRTYPES_is_valid
+	_have_nvme_cli_with_json_support
 }
 
 group_device_requires() {