On Fri, Mar 17, 2023 at 03:27:46PM -0500, Eric Blake wrote: > The NBD spec says the client handle (or cookie) is opaque on the > server, and therefore it really doesn't matter what endianness we use; > to date, the use of memcpy() between u64 and a char[8] has exposed > native endianness when treating the handle as a 64-bit number. No, memcpy() works fine for char[8], which doesn't break endianness. > However, since NBD protocol documents that everything else is in > network order, and tools like Wireshark will dump even the contents of > the handle as seen over the network, it's worth using a consistent > ordering regardless of the native endianness. > > Plus, using a consistent endianness now allows an upcoming patch to > simplify this to directly use integer assignment instead of memcpy(). It isn't necessary, given ->handle is actually u64, which is handled by nbd client only. > > Signed-off-by: Eric Blake <eblake@xxxxxxxxxx> > > --- > v2: new patch > --- > drivers/block/nbd.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c > index 592cfa8b765a..8a9487e79f1c 100644 > --- a/drivers/block/nbd.c > +++ b/drivers/block/nbd.c > @@ -560,6 +560,7 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index) > unsigned long size = blk_rq_bytes(req); > struct bio *bio; > u64 handle; > + __be64 tmp; > u32 type; > u32 nbd_cmd_flags = 0; > int sent = nsock->sent, skip = 0; > @@ -606,7 +607,8 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index) > request.len = htonl(size); > } > handle = nbd_cmd_handle(cmd); > - memcpy(request.handle, &handle, sizeof(handle)); > + tmp = cpu_to_be64(handle); > + memcpy(request.handle, &tmp, sizeof(tmp)); This way copies handle two times, really not fun. thanks, Ming
