Re: [Qemu-devel] [PATCH 1/1] nbd: fix max_discard/max_transfer_length

[Denis V. Lunev]

On 06/02/15 14:53, Kevin Wolf wrote:
> Am 06.02.2015 um 12:24 hat Denis V. Lunev geschrieben:
> > 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.
> >
> > NBD read/write code uses the same structure for transfers. Fix
> > max_transfer_length accordingly.
> >
> > Signed-off-by: Denis V. Lunev <address@hidden>
> > CC: Peter Lieven <address@hidden>
> > CC: Kevin Wolf <address@hidden>
> Thanks, I have applied both Peter's and your patch. Can you guys please
> check whether the current state of my block branch is correct or whether
> I forgot to include or remove some patch?
can you give me tree URL?

> By the way, I don't think this NBD patch is strictly necessary as you'll
> have a hard time finding a platform where INT_MAX > UINT32_MAX, but I
> think it's good documentation at least and a safeguard if we ever decide
> to lift the general block layer restrictions.
>
> Kevin
nope, it is absolutely mandatory

stdint.h:

/* Limit of `size_t' type.  */
# if __WORDSIZE == 64
#  define SIZE_MAX              (18446744073709551615UL)
# else
#  define SIZE_MAX              (4294967295U)
# endif

Den