Re: [Qemu-devel] [PATCHv3 0/9] cleanup/consolidate some iovec functions

[Michael Tokarev]

I created a git tree with these patches,
  git://git.corpit.ru/qemu.git branch mjt-iov

It includes one extra patch:

 6856d2ef3e72753aaa3bcdfc274ee6ae6c112dc6 virtio-serial-bus: use correct 
lengths in control_out() message

which has been discussed with Amit Shah and he suggested
me to include it in this series.

Thanks,

/mjt

On 12.03.2012 23:14, Michael Tokarev wrote:
> This is a little cleanup/consolidation for some iovec-related
> low-level routines in qemu.
> 
> The plan is to make library functions more understandable,
> consistent and useful, and to drop numerous implementations
> of the same thing.
> 
> The patch changes prototypes of several iov and qiov functions
> to match each other, changes types of arguments for some
> functions, _swaps_ some function arguments with each other,
> and makes use of common code in r/w path.
> 
> The result of all these changes.
> 
> 1. Most qiov-related (qemu_iovec_*) functions now accepts
>  'offset' parameter to specify from which (byte) position to
>  start operation.  This is added for _memset (removing
>  _memset_skip), _from_buffer (allowing to copy a bounce-
>  buffer to a middle of qiov).  Typical:
> 
>   void qemu_iovec_memset(QEMUIOVector *qiov, size_t offset, int c, size_t 
> bytes);
> 
> 2. All functions that accepts this `offset' argument does
>  it in a similar manner, following the
>    iov, fromwhere, what, bytes
>  pattern.  This is consistent with (updated) qemu_sendv()
>  and qemu_recvv() and friends, where `offset' and `bytes'
>  arguments were _renamed_, with the following prototypes:
> 
>    ssize_t qemu_sendv(sockfd, iov, size_t offset, size_t bytes)
> 
>  instead of
> 
>    int qemu_sendv(sockfd, iov, int len, int iov_offset)
> 
>  See how offset & bytes are used in the same way as for iov_*
>  and qemu_iovec_*.   A few callers of these are verified and
>  converted.
> 
> 3. Used size_t instead of various variations for byte counts.
>  Including qemu_iovec_copy which used uint64_t(!) type.
> 
> 4. Function arguments are renamed to better match with their
>  actual meaning.  Compare new and original prototype of
>  qemu_sendv() above: old prototype with `len' does not
>  tell if `len' refers to number of iov elements (as
>  regular writev() call) or to number of data bytes.
>  Ditto for several usages of `count' for some qemu_iovec_*,
>  which is also replaced to `bytes'.
> 
> 5. One implementation of the code remain. For example,
>  qemu_iovec_from_buffer() uses iov_from_buf() directly,
>  instead of repeating the same code.
> 
> The resulting function usage is much more consistent, the
> functions themselves are nice and understandable, which
> means they're easier to use and less error-prone.
> 
> This patchset also consolidates a few low-level send&recv
> functions into one, since both versions were exactly
> the same (and were finally calling common function anyway).
> This is done by exporting a common send_recv function with
> one extra bool argument, and making current send&recv to
> be just #defines.
> 
> And while at it all, also made some implementations shorter,
> cleaner and much easier to read/understand, and add some
> code comments.
> 
> The read&write consolidation has great potential for the
> block layer, as has been demonstrated before.
> Unification and generalization of qemu_iovec_* functions
> will let to optimize/simplify some more code in block/*,
> especially qemu_iovec_memset() and _from_buffer() (this
> optimization/simplification is already used in qcow2.c
> a bit).
> 
> The resulting thing should behave like current/existing
> code, there should be no behavor change at all, just
> some shuffling.  It has been tested slightly, by booting
> different guests out of different image formats and doing
> some i/o, after each of the 9 patches, and it all works
> correctly so far.
> 
> The patchset depends on a tiny patch I sent to Amit Shah,
> "virtio-serial-bus: use correct lengths in control_out() message"
> but the only conflict without that patch is in
> hw/virtio-serial-bus.c and it is trivial to resolve it.
> 
> Changes since v2:
> 
> - covered iov.[ch] with iov_*() functions which contained
>   similar functionality
> - changed tabs to spaces as per suggestion by Kevin
> - explicitly allow to use large sizes for frombuf/tobuf
>   functions and friends, stopping at the end of iovec
>   in case more bytes requested when available, and
>   _returning_ number of actual bytes processed, but
>   made it extra clear what a return value will be.
> - used ssize_t for sendv/recvv instead of int, to
>   be consistent with all system headers and other
>   places in qemu
> - fix/clarify a case in my qemu_co_sendv_recvv()
>   of handling zero reads(recvs) and writes(sends).
> - covered qemu_iovec_to_buf() to have the same
>   pattern as other too (was missing in v2), and
>   use it in qcow2.c right away to simplify things
> - spotted and removed wrong usage of qiov instead of
>   plain iov in posix-aio-compat.c
> 
> What is _not_ covered:
> 
> - suggestion by pbonzini to not use macros for
>   access methods to call sendv_recvv with an
>   extra true/false argument: I still think the
>   usage of macros here is better than anything
>   else.
> - maybe re-shuffling of all this stuff into
>   different headers -- we already have iov.h,
>   maybe rename it to qemu-iov.h for consistency
>   and move all iov-related functions into there
>   (and ditto for cutils.c => (qemu-)iov.c).
> 
> Michael Tokarev (9):
>   refresh iov_* functions
>   consolidate qemu_iovec_memset{,_skip}() into single function and use 
> existing iov_memset()
>   allow qemu_iovec_from_buffer() to specify offset from which to start copying
>   consolidate qemu_iovec_copy() and qemu_iovec_concat() and make them 
> consistent
>   change qemu_iovec_to_buf() to match other to,from_buf functions
>   change prototypes of qemu_sendv() and qemu_recvv()
>   export qemu_sendv_recvv() and use it in qemu_sendv() and qemu_recvv()
>   cleanup qemu_co_sendv(), qemu_co_recvv() and friends
>   rewrite and comment qemu_sendv_recvv()
> 
>  block.c                |   12 +-
>  block/curl.c           |    6 +-
>  block/iscsi.c          |    2 +-
>  block/nbd.c            |    4 +-
>  block/qcow.c           |    4 +-
>  block/qcow2.c          |   19 ++--
>  block/qed.c            |   10 +-
>  block/rbd.c            |    2 +-
>  block/sheepdog.c       |    6 +-
>  block/vdi.c            |    4 +-
>  cutils.c               |  261 +++++++++++++++++------------------------------
>  hw/9pfs/virtio-9p.c    |    8 +-
>  hw/rtl8139.c           |    2 +-
>  hw/usb.c               |    6 +-
>  hw/virtio-balloon.c    |    4 +-
>  hw/virtio-net.c        |    4 +-
>  hw/virtio-serial-bus.c |    6 +-
>  iov.c                  |   89 +++++++----------
>  iov.h                  |   47 ++++++++-
>  linux-aio.c            |    4 +-
>  net.c                  |    2 +-
>  posix-aio-compat.c     |    8 +-
>  qemu-common.h          |   69 +++++++------
>  qemu-coroutine-io.c    |   82 +++++-----------
>  24 files changed, 293 insertions(+), 368 deletions(-)
>