[Qemu-devel] [PATCH 2/2] nbd: fix max_discard

[Denis V. Lunev]

nbd_co_discard calls nbd_client_session_co_discard which uses uint32_t
as the length in bytes of the data to discard due to the following
definition:

struct nbd_request {
    uint32_t magic;
    uint32_t type;
    uint64_t handle;
    uint64_t from;
    uint32_t len; <-- the length of data to be discarded, in bytes
} QEMU_PACKED;

Thus we should limit bl_max_discard to UINT32_MAX >> BDRV_SECTOR_BITS to
avoid overflow.

Signed-off-by: Denis V. Lunev <address@hidden>
Reviewed-by: Peter Lieven <address@hidden>
CC: Kevin Wolf <address@hidden>
---
 block/nbd.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/block/nbd.c b/block/nbd.c
index 04cc845..99af713 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -301,6 +301,11 @@ static int nbd_co_flush(BlockDriverState *bs)
     return nbd_client_session_co_flush(&s->client);
 }
 
+static void nbd_refresh_limits(BlockDriverState *bs, Error **errp)
+{
+    bs->bl.max_discard = UINT32_MAX >> BDRV_SECTOR_BITS;
+}
+
 static int nbd_co_discard(BlockDriverState *bs, int64_t sector_num,
                           int nb_sectors)
 {
@@ -396,6 +401,7 @@ static BlockDriver bdrv_nbd = {
     .bdrv_close                 = nbd_close,
     .bdrv_co_flush_to_os        = nbd_co_flush,
     .bdrv_co_discard            = nbd_co_discard,
+    .bdrv_refresh_limits        = nbd_refresh_limits,
     .bdrv_getlength             = nbd_getlength,
     .bdrv_detach_aio_context    = nbd_detach_aio_context,
     .bdrv_attach_aio_context    = nbd_attach_aio_context,
@@ -413,6 +419,7 @@ static BlockDriver bdrv_nbd_tcp = {
     .bdrv_close                 = nbd_close,
     .bdrv_co_flush_to_os        = nbd_co_flush,
     .bdrv_co_discard            = nbd_co_discard,
+    .bdrv_refresh_limits        = nbd_refresh_limits,
     .bdrv_getlength             = nbd_getlength,
     .bdrv_detach_aio_context    = nbd_detach_aio_context,
     .bdrv_attach_aio_context    = nbd_attach_aio_context,
@@ -430,6 +437,7 @@ static BlockDriver bdrv_nbd_unix = {
     .bdrv_close                 = nbd_close,
     .bdrv_co_flush_to_os        = nbd_co_flush,
     .bdrv_co_discard            = nbd_co_discard,
+    .bdrv_refresh_limits        = nbd_refresh_limits,
     .bdrv_getlength             = nbd_getlength,
     .bdrv_detach_aio_context    = nbd_detach_aio_context,
     .bdrv_attach_aio_context    = nbd_attach_aio_context,
-- 
1.9.1