Re: [PATCH 1/2 V2] kvm tools: Add scatter-gather variants of IO functions

[Konstantin Khlebnikov <khlebnikov@parallels.com>]

Sasha Levin wrote:
> On Sun, 2011-04-17 at 14:03 +0400, Konstantin Khlebnikov wrote:
>> Avi Kivity wrote:
>>> What if nr is nonzero when the loop terminates?  You need to update the
>>> first iovec entry so you don't redo that segment.
>>
>> Oh yes, it is simple (hunk above), so "const" from prototype must be removed,
>> while original syscalls declare iov argument as const.
>
> The problem here is that if we start changing the internals of the iovec
> struct it forces us to copy it before calling the I/O functions since if
> we change it within the functions it's unusable to the caller anymore.
>
> Currently it's passed as a const because we only move pointers outside
> the struct.
>
> Basically the trade-off here is copying iovec before every read/write vs
> having to sometimes read data again (<  1 block), so I've went with the
> latter.
>
> Do you think it's better to go with the first alternative?
>
>

Or we can call one non-vectored operation for the rest of last io-verctor.