Re: [Libguestfs] [PATCH v4 16/24] nbd/server: Support 64-bit block status

The NBD spec states that if the client negotiates extended headers, the server must avoid NBD_REPLY_TYPE_BLOCK_STATUS and instead use NBD_REPLY_TYPE_BLOCK_STATUS_EXT which supports 64-bit lengths, even if the reply does not need more than 32 bits. As of this patch, client->mode is still never NBD_MODE_EXTENDED, so the code added here does not take effect until the next patch enables negotiation. For now, all metacontexts that we know how to export never populate more than 32 bits of information, so we don't have to worry about NBD_REP_ERR_EXT_HEADER_REQD or filtering during handshake, and we always send all zeroes for the upper 32 bits of status during NBD_CMD_BLOCK_STATUS. Note that we previously had some interesting size-juggling on call chains, such as: nbd_co_send_block_status(uint32_t length) -> blockstatus_to_extents(uint32_t bytes) -> bdrv_block_status_above(bytes, &uint64_t num) -> nbd_extent_array_add(uint64_t num) -> store num in 32-bit length But we were lucky that it never overflowed: bdrv_block_status_above never sets num larger than bytes, and we had previously been capping 'bytes' at 32 bits (since the protocol does not allow sending a larger request without extended headers). This patch adds some assertions that ensure we continue to avoid overflowing 32 bits for a narrow

@@ -2162,19 +2187,23 @@ static void nbd_extent_array_convert_to_be(NBDExtentArray *ea) * would result in an incorrect range reported to the client) */ static int nbd_extent_array_add(NBDExtentArray *ea, - uint32_t length, uint32_t flags) + uint64_t length, uint32_t flags) { assert(ea->can_add); if (!length) { return 0; } + if (!ea->extended) { + assert(length <= UINT32_MAX); + } /* Extend previous extent if flags are the same */ if (ea->count > 0 && flags == ea->extents[ea->count - 1].flags) { - uint64_t sum = (uint64_t)length + ea->extents[ea->count - 1].length; + uint64_t sum = length + ea->extents[ea->count - 1].length; - if (sum <= UINT32_MAX) { + assert(sum >= length); + if (sum <= UINT32_MAX || ea->extended) {