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.\"
.IX Title "nbd_trim 3"
.TH nbd_trim 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.
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.nh
.SH NAME
nbd_trim \- send trim command to the NBD server
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #include <libnbd.h>
\&
\& int nbd_trim (
\&       struct nbd_handle *h, uint64_t count,
\&       uint64_t offset, uint32_t flags
\&     );
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
Issue a trim command to the NBD server, which if supported
by the server causes a hole to be punched in the backing
store starting at \f(CW\*(C`offset\*(C'\fR and ending at \f(CW\*(C`offset\*(C'\fR + \f(CW\*(C`count\*(C'\fR \- 1.
The call returns when the command has been acknowledged by the server,
or there is an error.  Note this will generally return an error
if \fBnbd_can_trim\fR\|(3) is false or \fBnbd_is_read_only\fR\|(3) is true.
.PP
Note that not all servers can support a \f(CW\*(C`count\*(C'\fR of 4GiB or larger;
\&\fBnbd_get_extended_headers_negotiated\fR\|(3) indicates which servers
will parse a request larger than 32 bits.
The NBD protocol does not yet have a way for a client to learn if
the server will enforce an even smaller maximum trim size, although
a future extension may add a constraint visible in
\&\fBnbd_get_block_size\fR\|(3).
.PP
The \f(CW\*(C`flags\*(C'\fR parameter may be \f(CW0\fR for no flags, or may contain
\&\f(CW\*(C`LIBNBD_CMD_FLAG_FUA\*(C'\fR meaning that the server should not
return until the data has been committed to permanent storage
(if that is supported \- some servers cannot do this, see
\&\fBnbd_can_fua\fR\|(3)).
.PP
By default, libnbd will reject attempts to use this function with
parameters that are likely to result in server failure, such as
requesting an unknown command flag.  The \fBnbd_set_strict_mode\fR\|(3)
function can be used to alter which scenarios should await a server
reply rather than failing fast.
.SH "RETURN VALUE"
.IX Header "RETURN VALUE"
If the call is successful the function returns \f(CW0\fR.
.SH ERRORS
.IX Header "ERRORS"
On error \f(CW\-1\fR is returned.
.PP
Refer to "ERROR HANDLING" in \fBlibnbd\fR\|(3)
for how to get further details of the error.
.PP
The following parameters must not be NULL: \f(CW\*(C`h\*(C'\fR.
For more information see "Non-NULL parameters" in \fBlibnbd\fR\|(3).
.SH "HANDLE STATE"
.IX Header "HANDLE STATE"
nbd_trim
can be called when the handle is in the following state:
.PP
.Vb 8
\& ┌─────────────────────────────────────┬─────────────────────────┐
\& │ Handle created, before connecting   │ ❌ error                │
\& │ Connecting                          │ ❌ error                │
\& │ Connecting & handshaking (opt_mode) │ ❌ error                │
\& │ Connected to the server             │ ✅ allowed              │
\& │ Connection shut down                │ ❌ error                │
\& │ Handle dead                         │ ❌ error                │
\& └─────────────────────────────────────┴─────────────────────────┘
.Ve
.SH VERSION
.IX Header "VERSION"
This function first appeared in libnbd 1.0.
.PP
If you need to test if this function is available at compile time
check if the following macro is defined:
.PP
.Vb 1
\& #define LIBNBD_HAVE_NBD_TRIM 1
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbd_aio_trim\fR\|(3),
\&\fBnbd_can_fua\fR\|(3),
\&\fBnbd_can_trim\fR\|(3),
\&\fBnbd_create\fR\|(3),
\&\fBnbd_get_block_size\fR\|(3),
\&\fBnbd_get_extended_headers_negotiated\fR\|(3),
\&\fBnbd_is_read_only\fR\|(3),
\&\fBnbd_set_strict_mode\fR\|(3),
\&\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