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.\" ========================================================================
.\"
.IX Title "nbd_create 3"
.TH nbd_create 3 2024-05-31 libnbd-1.20.0 LIBNBD
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH NAME
nbd_create, nbd_close, nbd_get_error, nbd_get_errno \- create libnbd
handles and fetch errors
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #include <libnbd.h>
.Ve
.PP
.Vb 1
\& struct nbd_handle *nbd;
.Ve
.PP
.Vb 1
\& struct nbd_handle *nbd_create (void);
.Ve
.PP
.Vb 1
\& void nbd_close (struct nbd_handle *nbd);
.Ve
.PP
.Vb 1
\& const char *nbd_get_error (void);
.Ve
.PP
.Vb 1
\& int nbd_get_errno (void);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\fBstruct nbd_handle\fR is an opaque structure which describes an NBD
client handle and the connection to an NBD server.
.SS "Creating a libnbd handle"
.IX Subsection "Creating a libnbd handle"
\&\fBnbd_create\fR creates a new handle.  It returns a pointer to the
opaque handle structure.
.PP
On error this returns \f(CW\*(C`NULL\*(C'\fR.  See "ERROR HANDLING" in \fBlibnbd\fR\|(3)
for how to get further details of the error.
.SS "Closing a handle"
.IX Subsection "Closing a handle"
\&\fBnbd_close\fR closes the handle, closing and freeing any associated
resources.
.PP
The final status of any command that has not been retired (whether by
\&\fBnbd_aio_command_completed\fR\|(3) or by a low-level completion callback
returning \f(CW1\fR) is lost.
.PP
This function is not safe to call while any other thread is still
using any \f(CW\*(C`nbd_*\*(C'\fR API on the same handle.  This function can block in
the case where we wait for a subprocess (eg. one created with
\&\fBnbd_connect_command\fR\|(3)).
.SS "Getting the latest error message in the thread"
.IX Subsection "Getting the latest error message in the thread"
\&\fBnbd_get_error\fR returns the most recent error message in the current
thread.  The error message is only valid if called immediately after
the failing call, from the same thread.  The error string returned
will be freed up next time any libnbd API is called from the same
thread, so if you need to keep it you must make a copy.
.PP
This should never return \f(CW\*(C`NULL\*(C'\fR provided there was an error
returned from the immediately preceding libnbd call in the
current thread.
.PP
\&\fBnbd_get_errno\fR returns the most recent \f(CW\*(C`errno\*(C'\fR in the current
thread.  Not all errors have corresponding errnos, so even if there
has been an error this may return \f(CW0\fR.  Error codes are the standard
ones from \f(CW\*(C`<errno.h>\*(C'\fR.
.PP
See "ERROR HANDLING" in \fBlibnbd\fR\|(3) for more discussion of how error
handling works in libnbd.
.SH EXAMPLE
.IX Header "EXAMPLE"
.Vb 1
\& #include <libnbd.h>
\&
\& main ()
\& {
\&   struct nbd_handle *nbd;
\&
\&   nbd = nbd_create ();
\&   if (nbd == NULL) {
\&     fprintf (stderr, "%s\en", nbd_get_error ());
\&     nbd_close (nbd);
\&     exit (EXIT_FAILURE);
\&   }
\&   nbd_close (nbd);
\&   exit (EXIT_SUCCESS);
\& }
.Ve
.SH VERSION
.IX Header "VERSION"
These functions were all present in libnbd 1.0.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBlibnbd\fR\|(3).
.SH AUTHORS
.IX Header "AUTHORS"
Eric Blake
.PP
Richard W.M. Jones
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright Red Hat
.SH LICENSE
.IX Header "LICENSE"
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.
.PP
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.
.PP
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110\-1301 USA