Make it much more understandable, add a missing
iov_cnt argument (number of iovs in the iov), and
add comments to it.

The new implementation has been extensively tested
by splitting a large buffer into many small
randomly-sized chunks, sending it over socket to
another, slow process and verifying the receiving
data is the same.

Also add a unit test for iov_send_recv(), sending/
receiving data between two processes over a socketpair
using random vectors and random sizes.
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

Rename do_sendv_recvv() to iov_send_recv(), change its last arg
(do_send) from int to bool, export it in iov.h, and made the two
callers of it (iov_send() and iov_recv()) to be trivial #defines
just adding 5th arg.

iov_send_recv() will be used later.
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

Rename arguments and use size_t for sizes instead of int,
from
 int
 qemu_sendv(int sockfd, struct iovec *iov,
            int len, int iov_offset)
to
 ssize_t
 iov_send(int sockfd, struct iovec *iov,
          size_t offset, size_t bytes)

The main motivation was to make it clear that length
and offset are in _bytes_, not in iov elements: it was
very confusing before, because all standard functions
which deals with iovecs expects number of iovs, not
bytes, even the fact that struct iovec has iov_len and
iov_ prefix does not help.  With "bytes" and "offset",
especially since they're now size_t, it is much more
explicit.  Also change the return type to be ssize_t
instead of int.

This also changes it to match other iov-related functons,
but not _quite_: there's still no argument indicating
where iovec ends, ie, no iov_cnt parameter as used
in iov_size() and friends.  If will be added in subsequent
patch/rewrite.

All callers of qemu_sendv() and qemu_recvv() and
related, like qemu_co_sendv() and qemu_co_recvv(),
were checked to verify that it is safe to use unsigned
datatype instead of int.

Note that the order of arguments is changed to: offset
and bytes (len and iov_offset) are swapped with each
other.  This is to make them consistent with very similar
functions from qemu_iovec family, where offset always
follows qiov, to mean the place in it to start from.
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

This changes implementations of all iov_*
functions, completing the previous step.

All iov_* functions now ensure that this offset
argument is within the iovec (using assertion),
but lets to specify `bytes' value larger than
actual length of the iovec - in this case they
stops at the actual end of iovec.  It is also
suggested to use convinient `-1' value as `bytes'
to mean just this -- "up to the end".

There's one very minor semantic change here: new
requiriment is that `offset' points to inside of
iovec.  This is checked just at the end of functions
(assert()), it does not actually need to be enforced,
but using any of these functions with offset pointing
past the end of iovec is wrong anyway.

Note: the new code in iov.c uses arithmetic with
void pointers.  I thought this is not supported
everywhere and is a GCC extension (indeed, the C
standard does not define void arithmetic).  However,
the original code already use void arith in
iov_from_buf() function:
  (memcpy(..., buf + buf_off,...)
which apparently works well so far (it is this
way in qemu 1.0).  So I left it this way and used
it in other places.

While at it, add a unit-test file test-iov.c,
to check various corner cases with iov_from_buf(),
iov_to_buf() and iov_memset().
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

Reorder arguments to be more natural, readable and
consistent with other iov_* functions, and change
argument names, from:
 iov_from_buf(iov, iov_cnt, buf, iov_off, size)
to
 iov_from_buf(iov, iov_cnt, offset, buf, bytes)

The result becomes natural English:

 copy data to this `iov' vector with `iov_cnt'
 elements starting at byte offset `offset'
 from memory buffer `buf', processing `bytes'
 bytes max.

(Try to read the original prototype this way).

Also change iov_clear() to more general iov_memset()
(it uses memset() internally anyway).

While at it, add comments to the header file
describing what the routines actually does.

The patch only renames argumens in the header, but
keeps old names in the implementation.  The next
patch will touch actual code to match.

Now, it might look wrong to pay so much attention
to so small things.  But we've so many badly designed
interfaces already so the whole thing becomes rather
confusing or error prone.  One example of this is
previous commit and small discussion which emerged
from it, with an outcome that the utility functions
like these aren't well-understdandable, leading to
strange usage cases.  That's why I paid quite some
attention to this set of functions and a few
others in subsequent patches.
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

Fill the spefified area with zeros.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

Useful for debugging purposes.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

iov_to_buf() has an 'offset' parameter, iov_from_buf() hasn't.
This patch adds the missing parameter to iov_from_buf().
It also renames the 'offset' parameter to 'iov_off' to
emphasize it's the offset into the iovec and not the buffer.
Signed-off-by: NHannes Reinecke <hare@suse.de>
Acked-by: NAlexander Graf <agraf@suse.de>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

The iov functions can be useful to other code as well.
Signed-off-by: NAmit Shah <amit.shah@redhat.com>
CC: Christoph Hellwig <hch@lst.de>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

iov_to_buf() puts the buffer contents in the iov in a linearized buffer.

iov_size() gets the length of the contents in the iov.

The iov_to_buf() function is the memcpy_to_iovec() function that was
used in virtio-ballon.c.
Signed-off-by: NAmit Shah <amit.shah@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

The virtio-net code uses iov_fill() which fills an iov from a linear
buffer. The virtio-serial-bus code does something similar in an
open-coded function.

Create a new iov.c file that has iov_from_buf().

Convert virtio-net and virtio-serial-bus over to use this functionality.
virtio-net used ints to hold sizes, the new function is going to use
size_t types.

Later commits will add the opposite functionality -- going from an iov
to a linear buffer.
Signed-off-by: NAmit Shah <amit.shah@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>