On Fri, Nov 12, 2021 at 10:13:01AM +0000, Daniel P. Berrangé wrote: > On Fri, Nov 12, 2021 at 02:10:36AM -0300, Leonardo Bras wrote: > > Adds io_writev_zerocopy and io_flush_zerocopy as optional callback to > > QIOChannelClass, > > allowing the implementation of zerocopy writes by subclasses. > > > > How to use them: > > - Write data using qio_channel_writev_zerocopy(), > > - Wait write completion with qio_channel_flush_zerocopy(). > > > > Notes: > > As some zerocopy implementations work asynchronously, it's > > recommended to keep the write buffer untouched until the return of > > qio_channel_flush_zerocopy(), to avoid the risk of sending an updated > > buffer instead of the one at the write. > > > > As the new callbacks are optional, if a subclass does not implement them, > > then: > > - io_writev_zerocopy will return -1, > > - io_flush_zerocopy will return 0 without changing anything. > > > > Also, some functions like qio_channel_writev_full_all() were adapted to > > receive a flag parameter. That allows shared code between zerocopy and > > non-zerocopy writev. > > > > Signed-off-by: Leonardo Bras <leob...@redhat.com> > > --- > > include/io/channel.h | 93 ++++++++++++++++++++++++++++++++++++++------ > > io/channel.c | 65 +++++++++++++++++++++++++------ > > 2 files changed, 135 insertions(+), 23 deletions(-) > > > > diff --git a/include/io/channel.h b/include/io/channel.h > > index 88988979f8..a19c09bb84 100644 > > --- a/include/io/channel.h > > +++ b/include/io/channel.h
> > +/** > > + * qio_channel_writev_zerocopy: > > + * @ioc: the channel object > > + * @iov: the array of memory regions to write data from > > + * @niov: the length of the @iov array > > + * @errp: pointer to a NULL-initialized error object > > + * > > + * Behaves like qio_channel_writev_full_all_flags, but may write > > qio_channel_writev > > > + * data asynchronously while avoiding unnecessary data copy. > > + * This function may return before any data is actually written, > > + * but should queue every buffer for writing. > > Callers mustn't rely on "should" docs - they must rely on the > return value indicating how many bytes were accepted. Also mention that this requires locked memory and can/will fail if insufficient locked memory is available. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
