.\" -*- mode: troff; coding: utf-8 -*- .\" Automatically generated by Podwrapper::Man 1.20.0 (Pod::Simple 3.43) .\" .\" Standard preamble: .\" ======================================================================== .de Sp \" Vertical space (when we can't use .PP) .if t .sp .5v .if n .sp .. .de Vb \" Begin verbatim text .ft CW .nf .ne \\$1 .. .de Ve \" End verbatim text .ft R .fi .. .\" \*(C` and \*(C' are quotes in nroff, nothing in troff, for use with C<>. .ie n \{\ . ds C` "" . ds C' "" 'br\} .el\{\ . ds C` . ds C' 'br\} .\" .\" Escape single quotes in literal strings from groff's Unicode transform. .ie \n(.g .ds Aq \(aq .el .ds Aq ' .\" .\" If the F register is >0, we'll generate index entries on stderr for .\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index .\" entries marked with X<> in POD. Of course, you'll have to process the .\" output yourself in some meaningful fashion. .\" .\" Avoid warning from groff about undefined register 'F'. .de IX .. .nr rF 0 .if \n(.g .if rF .nr rF 1 .if (\n(rF:(\n(.g==0)) \{\ . if \nF \{\ . de IX . tm Index:\\$1\t\\n%\t"\\$2" .. . if !\nF==2 \{\ . nr % 0 . nr F 2 . \} . \} .\} .rr rF .\" ======================================================================== .\" .IX Title "nbd_cache 3" .TH nbd_cache 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_cache \- send cache (prefetch) command to the NBD server .SH SYNOPSIS .IX Header "SYNOPSIS" .Vb 1 \& #include \& \& int nbd_cache ( \& struct nbd_handle *h, uint64_t count, \& uint64_t offset, uint32_t flags \& ); .Ve .SH DESCRIPTION .IX Header "DESCRIPTION" Issue the cache (prefetch) command to the NBD server, which if supported by the server causes data to be prefetched into faster storage by the server, speeding up a subsequent \&\fBnbd_pread\fR\|(3) call. The server can also silently ignore this command. Note this will generally return an error if \&\fBnbd_can_cache\fR\|(3) is false. .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 cache 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 must be \f(CW0\fR for now (it exists for future NBD protocol extensions). .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_cache 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_CACHE 1 .Ve .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBnbd_aio_cache\fR\|(3), \&\fBnbd_can_cache\fR\|(3), \&\fBnbd_create\fR\|(3), \&\fBnbd_get_block_size\fR\|(3), \&\fBnbd_get_extended_headers_negotiated\fR\|(3), \&\fBnbd_pread\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