3 files changed, 36 insertions, 2 deletions

diff --git a/block.c b/block.c
index f184b376da..4582961965 100644
--- a/block.c
+++ b/block.c
@@ -581,6 +581,26 @@ static int refresh_total_sectors(BlockDriverState *bs, int64_t hint)
 }
 
 /**
+ * Set open flags for a given discard mode
+ *
+ * Return 0 on success, -1 if the discard mode was invalid.
+ */
+int bdrv_parse_discard_flags(const char *mode, int *flags)
+{
+    *flags &= ~BDRV_O_UNMAP;
+
+    if (!strcmp(mode, "off") || !strcmp(mode, "ignore")) {
+        /* do nothing */
+    } else if (!strcmp(mode, "on") || !strcmp(mode, "unmap")) {
+        *flags |= BDRV_O_UNMAP;
+    } else {
+        return -1;
+    }
+
+    return 0;
+}
+
+/**
  * Set open flags for a given cache mode
  *
  * Return 0 on success, -1 if the cache mode was invalid.
@@ -4191,6 +4211,11 @@ int coroutine_fn bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
         bdrv_reset_dirty(bs, sector_num, nb_sectors);
     }
 
+    /* Do nothing if disabled.  */
+    if (!(bs->open_flags & BDRV_O_UNMAP)) {
+        return 0;
+    }
+
     if (bs->drv->bdrv_co_discard) {
         return bs->drv->bdrv_co_discard(bs, sector_num, nb_sectors);
     } else if (bs->drv->bdrv_aio_discard) {
diff --git a/include/block/block.h b/include/block/block.h
index b4a24da3e9..0f750d7da3 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -84,6 +84,7 @@ typedef struct BlockDevOps {
 #define BDRV_O_INCOMING    0x0800  /* consistency hint for incoming migration */
 #define BDRV_O_CHECK       0x1000  /* open solely for consistency check */
 #define BDRV_O_ALLOW_RDWR  0x2000  /* allow reopen to change from r/o to r/w */
+#define BDRV_O_UNMAP       0x4000  /* execute guest UNMAP/TRIM operations */
 
 #define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_CACHE_WB | BDRV_O_NO_FLUSH)
 
@@ -133,6 +134,7 @@ void bdrv_swap(BlockDriverState *bs_new, BlockDriverState *bs_old);
 void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top);
 void bdrv_delete(BlockDriverState *bs);
 int bdrv_parse_cache_flags(const char *mode, int *flags);
+int bdrv_parse_discard_flags(const char *mode, int *flags);
 int bdrv_file_open(BlockDriverState **pbs, const char *filename, int flags);
 int bdrv_open_backing_file(BlockDriverState *bs);
 int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
diff --git a/qemu-io.c b/qemu-io.c
index 61880932b3..7b3de42773 100644
--- a/qemu-io.c
+++ b/qemu-io.c
@@ -1899,7 +1899,7 @@ int main(int argc, char **argv)
 {
     int readonly = 0;
     int growable = 0;
-    const char *sopt = "hVc:rsnmgkt:T:";
+    const char *sopt = "hVc:d:rsnmgkt:T:";
     const struct option lopt[] = {
         { "help", 0, NULL, 'h' },
         { "version", 0, NULL, 'V' },
@@ -1911,13 +1911,14 @@ int main(int argc, char **argv)
         { "misalign", 0, NULL, 'm' },
         { "growable", 0, NULL, 'g' },
         { "native-aio", 0, NULL, 'k' },
+        { "discard", 1, NULL, 'd' },
         { "cache", 1, NULL, 't' },
         { "trace", 1, NULL, 'T' },
         { NULL, 0, NULL, 0 }
     };
     int c;
     int opt_index = 0;
-    int flags = 0;
+    int flags = BDRV_O_UNMAP;
 
     progname = basename(argv[0]);
 
@@ -1929,6 +1930,12 @@ int main(int argc, char **argv)
         case 'n':
             flags |= BDRV_O_NOCACHE | BDRV_O_CACHE_WB;
             break;
+        case 'd':
+            if (bdrv_parse_discard_flags(optarg, &flags) < 0) {
+                error_report("Invalid discard option: %s", optarg);
+                exit(1);
+            }
+            break;
         case 'c':
             add_user_command(optarg);
             break;