[Qemu-devel] [PATCH] block: split large discard requests from block frontend

[Olaf Hering <olaf@aepfle.de>]

Large discard requests lead to sign expansion errors in qemu.
Since there is no API to tell a guest about the limitations qmeu
has to split a large request itself.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
---
 block/io.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/block/io.c b/block/io.c
index c4869b9..5b6ed58 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2442,7 +2442,7 @@ static void coroutine_fn bdrv_discard_co_entry(void *opaque)
     rwco->ret = bdrv_co_discard(rwco->bs, rwco->sector_num, rwco->nb_sectors);
 }
 
-int coroutine_fn bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
+static int __bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
                                  int nb_sectors)
 {
     BdrvTrackedRequest req;
@@ -2524,6 +2524,26 @@ out:
     return ret;
 }
 
+int coroutine_fn bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
+                                 int nb_sectors)
+{
+    int num, ret;
+    int limit = BDRV_REQUEST_MAX_SECTORS;
+    int remaining = nb_sectors;
+    int64_t sector_offset = sector_num;
+
+    do {
+        num = remaining > limit ? limit : remaining;
+        ret = __bdrv_co_discard(bs, sector_offset, num);
+        if (ret < 0)
+            break;
+        remaining -= num;
+        sector_offset += num;
+    } while (remaining > 0);
+
+    return ret;
+}
+
 int bdrv_discard(BlockDriverState *bs, int64_t sector_num, int nb_sectors)
 {
     Coroutine *co;