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>

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 =

blockdev.c

@@ -356,7 +356,6 @@ static void extract_common_blockdev_options(QemuOpts *opts, int *bdrv_flags,
     const char **throttling_group, ThrottleConfig *throttle_cfg,
     BlockdevDetectZeroesOptions *detect_zeroes, Error **errp)
 {
-    const char *discard;
     Error *local_error = NULL;
     const char *aio;
 
@@ -365,13 +364,6 @@ static void extract_common_blockdev_options(QemuOpts *opts, int *bdrv_flags,
             *bdrv_flags |= BDRV_O_COPY_ON_READ;
         }
 
-        if ((discard = qemu_opt_get(opts, "discard")) != NULL) {
-            if (bdrv_parse_discard_flags(discard, bdrv_flags) != 0) {
-                error_setg(errp, "Invalid discard option");
-                return;
-            }
-        }
-
         if ((aio = qemu_opt_get(opts, "aio")) != NULL) {
             if (!strcmp(aio, "native")) {
                 *bdrv_flags |= BDRV_O_NATIVE_AIO;
@@ -449,15 +441,6 @@ static void extract_common_blockdev_options(QemuOpts *opts, int *bdrv_flags,
             error_propagate(errp, local_error);
             return;
         }
-
-        if (bdrv_flags &&
-            *detect_zeroes == BLOCKDEV_DETECT_ZEROES_OPTIONS_UNMAP &&
-            !(*bdrv_flags & BDRV_O_UNMAP))
-        {
-            error_setg(errp, "setting detect-zeroes to unmap is not allowed "
-                             "without setting discard operation to unmap");
-            return;
-        }
     }
 }
 
@@ -3989,10 +3972,6 @@ QemuOptsList qemu_common_drive_opts = {
             .name = "snapshot",
             .type = QEMU_OPT_BOOL,
             .help = "enable/disable snapshot mode",
-        },{
-            .name = "discard",
-            .type = QEMU_OPT_STRING,
-            .help = "discard operation (ignore/off, unmap/on)",
         },{
             .name = "aio",
             .type = QEMU_OPT_STRING,
@@ -4125,10 +4104,6 @@ static QemuOptsList qemu_root_bds_opts = {
     .head = QTAILQ_HEAD_INITIALIZER(qemu_root_bds_opts.head),
     .desc = {
         {
-            .name = "discard",
-            .type = QEMU_OPT_STRING,
-            .help = "discard operation (ignore/off, unmap/on)",
-        },{
             .name = "aio",
             .type = QEMU_OPT_STRING,
             .help = "host AIO implementation (threads, native)",

include/block/block.h

@@ -108,6 +108,7 @@ typedef struct HDGeometry {
 #define BDRV_OPT_CACHE_DIRECT   "cache.direct"
 #define BDRV_OPT_CACHE_NO_FLUSH "cache.no-flush"
 #define BDRV_OPT_READ_ONLY      "read-only"
+#define BDRV_OPT_DISCARD        "discard"
 
 
 #define BDRV_SECTOR_BITS   9