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

[Michael Tokarev <mjt@tls.msk.ru>]

his 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(-)

-- 
1.7.9.1