block: Move 'discard' option to bdrv_open_common()

This enables its use for nested child nodes. The compatibility
between the 'discard' and 'detect-zeroes' setting is checked in
bdrv_open_common() now as the former setting isn't available before
calling bdrv_open() any more.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

1 files changed, 16 insertions, 1 deletions

diff --git a/block.c b/block.c
index 1f1045738d..bb1f1ec957 100644
--- a/block.c
+++ b/block.c
@@ -765,7 +765,7 @@ static void bdrv_inherited_options(int *child_flags, QDict *child_options,
     /* Our block drivers take care to send flushes and respect unmap policy,
      * so we can default to enable both on lower layers regardless of the
      * corresponding parent options. */
-    flags |= BDRV_O_UNMAP;
+    qdict_set_default_str(child_options, BDRV_OPT_DISCARD, "unmap");
 
     /* Clear flags that only apply to the top layer */
     flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING | BDRV_O_COPY_ON_READ |
@@ -960,6 +960,11 @@ static QemuOptsList bdrv_runtime_opts = {
             .type = QEMU_OPT_STRING,
             .help = "try to optimize zero writes (off, on, unmap)",
         },
+        {
+            .name = "discard",
+            .type = QEMU_OPT_STRING,
+            .help = "discard operation (ignore/off, unmap/on)",
+        },
         { /* end of list */ }
     },
 };
@@ -976,6 +981,7 @@ static int bdrv_open_common(BlockDriverState *bs, BdrvChild *file,
     const char *filename;
     const char *driver_name = NULL;
     const char *node_name = NULL;
+    const char *discard;
     const char *detect_zeroes;
     QemuOpts *opts;
     BlockDriver *drv;
@@ -1045,6 +1051,15 @@ static int bdrv_open_common(BlockDriverState *bs, BdrvChild *file,
         }
     }
 
+    discard = qemu_opt_get(opts, "discard");
+    if (discard != NULL) {
+        if (bdrv_parse_discard_flags(discard, &bs->open_flags) != 0) {
+            error_setg(errp, "Invalid discard option");
+            ret = -EINVAL;
+            goto fail_opts;
+        }
+    }
+
     detect_zeroes = qemu_opt_get(opts, "detect-zeroes");
     if (detect_zeroes) {
         BlockdevDetectZeroesOptions value =