tests/qemu-iotests: introduce filter for qemu-nbd export list

Introduce a filter for the output of qemu-nbd export list so it can be
reused in multiple tests.

The filter is a bit more permissive that what test 241 currently uses,
as its allows printing of the export count, along with any possible
error messages that might be emitted.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20220304193610.3293146-9-berrange@redhat.com>
Tested-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

tests/qemu-iotests/241

@@ -58,7 +58,7 @@ echo
 
 nbd_server_start_unix_socket -f $IMGFMT "$TEST_IMG_FILE"
 
-$QEMU_NBD_PROG --list -k $nbd_unix_socket | grep '\(size\|min\)'
+$QEMU_NBD_PROG --list -k $nbd_unix_socket | _filter_qemu_nbd_exports
 $QEMU_IMG map -f raw --output=json "$TEST_IMG" | _filter_qemu_img_map
 $QEMU_IO -f raw -c map "$TEST_IMG"
 nbd_server_stop
@@ -71,7 +71,7 @@ echo
 # sector alignment, here at the server.
 nbd_server_start_unix_socket "$TEST_IMG_FILE" 2> "$TEST_DIR/server.log"
 
-$QEMU_NBD_PROG --list -k $nbd_unix_socket | grep '\(size\|min\)'
+$QEMU_NBD_PROG --list -k $nbd_unix_socket | _filter_qemu_nbd_exports
 $QEMU_IMG map -f raw --output=json "$TEST_IMG" | _filter_qemu_img_map
 $QEMU_IO -f raw -c map "$TEST_IMG"
 nbd_server_stop
@@ -84,7 +84,7 @@ echo
 # Now force sector alignment at the client.
 nbd_server_start_unix_socket -f $IMGFMT "$TEST_IMG_FILE"
 
-$QEMU_NBD_PROG --list -k $nbd_unix_socket | grep '\(size\|min\)'
+$QEMU_NBD_PROG --list -k $nbd_unix_socket | _filter_qemu_nbd_exports
 $QEMU_IMG map --output=json "$TEST_IMG" | _filter_qemu_img_map
 $QEMU_IO -c map "$TEST_IMG"
 nbd_server_stop

tests/qemu-iotests/241.out

@@ -2,6 +2,8 @@ QA output created by 241
 
 === Exporting unaligned raw image, natural alignment ===
 
+exports available: 1
+ export: ''
   size:  1024
   min block: 1
 [{ "start": 0, "length": 1000, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
@@ -10,6 +12,8 @@ QA output created by 241
 
 === Exporting unaligned raw image, forced server sector alignment ===
 
+exports available: 1
+ export: ''
   size:  1024
   min block: 512
 [{ "start": 0, "length": 1024, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET}]
@@ -20,6 +24,8 @@ WARNING: Image format was not specified for 'TEST_DIR/t.raw' and probing guessed
 
 === Exporting unaligned raw image, forced client sector alignment ===
 
+exports available: 1
+ export: ''
   size:  1024
   min block: 1
 [{ "start": 0, "length": 1000, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},

tests/qemu-iotests/common.filter

@@ -309,6 +309,11 @@ _filter_nbd()
         -e 's#\(foo\|PORT/\?\|.sock\): Failed to .*$#\1#'
 }
 
+_filter_qemu_nbd_exports()
+{
+    grep '\(exports available\|export\|size\|min block\|qemu-nbd\):'
+}
+
 _filter_qmp_empty_return()
 {
     grep -v '{"return": {}}'