.TH gensio_write 3 "24 Feb 2019"
.SH NAME
gensio_write \- Write data to a gensio
.SH SYNOPSIS
.B #include <gensio/gensio.h>
.TP 20
.B int gensio_write(struct gensio *io, gensiods *count,
.br
.B                   const void *buf, gensiods buflen,
.br
.B                   const char *const *auxdata);
.PP
.B struct gensio_sg {
.RS 4
.B     const void *buf;
.br
.B     gensiods buflen;
.RE
.B };
.TP 20
.B int gensio_write_sg(struct gensio *io, gensiods *count,
.br
.B                   const struct gensio_sg *sg, gensiods sglen,
.br
.B                   const char *const *auxdata);
.SH "DESCRIPTION"
Write data to the given gensio.  The data is in
.I buf
and the length of
the data is in
.I buflen.
Note that
.B gensio_write
may not write all of the data given, depending on the gensio type and
the internal buffer space.  It will return the number of bytes actually
written in
.B count
which may be NULL if you don't care.  (Hint: you should almost always
care.)

If
.B gensio_write
is unable to write the full amount of data, you should generally buffer
the unwritten data and call
.B gensio_set_write_callback_enable(3)
to know when you can write the rest of the data.  Many applications
always buffer the data and enable the write callback to do the write
and then disable the write callback when all data is written, for
consistency.

.B gensio_write
will never block, if it cannot write all the data it will write what
it can and return.

.B auxdata
is used to pass in gensio specific auxiliary data, such as the stream
number for SCTP or whether the data is out of band data for SCTP or
TCP.

.B gensio_write_sg
is like
.B gensio_write,
but it takes a scatter-gather structure to allow you to combine multiple
chunks of data without copying.  Note that if you get a partial write,
you must figure out where the write ended in your scatter-gather list
and start the next write from there.
.SH "RETURN VALUES"
Zero is returned on success, or a gensio error on failure.
.SH "SEE ALSO"
gensio_err(3), gensio(5)