.\" Automatically generated by Podwrapper::Man 1.6.1 (Pod::Simple 3.40) .\" .\" 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 .. .\" Set up some character translations and predefined strings. \*(-- will .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left .\" double quote, and \*(R" will give a right double quote. \*(C+ will .\" give a nicer C++. Capital omega is used to do unbreakable dashes and .\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff, .\" nothing in troff, for use with C<>. .tr \(*W- .ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' .ie n \{\ . ds -- \(*W- . ds PI pi . if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch . if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch . ds L" "" . ds R" "" . ds C` "" . ds C' "" 'br\} .el\{\ . ds -- \|\(em\| . ds PI \(*p . ds L" `` . ds R" '' . 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_pwrite 3" .TH nbd_pwrite 3 "2021-02-09" "libnbd-1.6.1" "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_pwrite \- write to the NBD server .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #include \& \& int nbd_pwrite (struct nbd_handle *h, const void *buf, \& size_t count, uint64_t offset, \& uint32_t flags); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" Issue a write command to the \s-1NBD\s0 server, writing the data in \&\f(CW\*(C`buf\*(C'\fR to the range starting at \f(CW\*(C`offset\*(C'\fR and ending at \&\f(CW\*(C`offset\*(C'\fR + \f(CW\*(C`count\*(C'\fR \- 1. \s-1NBD\s0 can only write all or nothing using this call. 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_is_read_only\fR\|(3) is true. .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\*(C`\-1\*(C'\fR is returned. .PP Refer to \*(L"\s-1ERROR HANDLING\*(R"\s0 in \fBlibnbd\fR\|(3) for how to get further details of the error. .SH "HANDLE STATE" .IX Header "HANDLE STATE" The handle must be connected with the server, otherwise this call will return an error. .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_PWRITE 1 .Ve .SH "EXAMPLE" .IX Header "EXAMPLE" This example is also available as \fIexamples/reads\-and\-writes.c\fR in the libnbd source code. .PP .Vb 10 \& /* This example shows how to do synchronous reads \& * and writes randomly over the first megabyte of an \& * NBD server. Note this will destroy any existing \& * content on the NBD server. \& * \& * To test it with nbdkit and a RAM disk: \& * \& * nbdkit \-U \- memory 1M \e \& * \-\-run \*(Aq./simple\-reads\-and\-writes $unixsocket\*(Aq \& */ \& \& #include \& #include \& #include \& #include \& #include \& \& #include \& \& int \& main (int argc, char *argv[]) \& { \& struct nbd_handle *nbd; \& char buf[512]; \& size_t i; \& int64_t exportsize; \& uint64_t offset; \& \& srand (time (NULL)); \& \& if (argc != 2) { \& fprintf (stderr, "%s socket\en", argv[0]); \& exit (EXIT_FAILURE); \& } \& \& /* Create the libnbd handle. */ \& nbd = nbd_create (); \& if (nbd == NULL) { \& fprintf (stderr, "%s\en", nbd_get_error ()); \& exit (EXIT_FAILURE); \& } \& \& /* Connect to the NBD server over a \& * Unix domain socket. \& */ \& if (nbd_connect_unix (nbd, argv[1]) == \-1) { \& fprintf (stderr, "%s\en", nbd_get_error ()); \& exit (EXIT_FAILURE); \& } \& \& /* Get the size of the disk and check \& * it\*(Aqs large enough. \& */ \& exportsize = nbd_get_size (nbd); \& if (exportsize == \-1) { \& fprintf (stderr, "%s\en", nbd_get_error ()); \& exit (EXIT_FAILURE); \& } \& assert (exportsize >= sizeof buf); \& \& /* Check that the server is writable. */ \& if (nbd_is_read_only (nbd) == 1) { \& fprintf (stderr, "%s: " \& "error: this NBD export is read\-only\en", \& argv[0]); \& exit (EXIT_FAILURE); \& } \& \& for (i = 0; i < sizeof buf; ++i) \& buf[i] = rand (); \& \& /* 1000 writes. */ \& for (i = 0; i < 1000; ++i) { \& offset = rand () % (exportsize \- sizeof buf); \& \& if (nbd_pwrite (nbd, buf, sizeof buf, \& offset, 0) == \-1) { \& fprintf (stderr, "%s\en", nbd_get_error ()); \& exit (EXIT_FAILURE); \& } \& } \& \& /* 1000 reads and writes. */ \& for (i = 0; i < 1000; ++i) { \& offset = rand () % (exportsize \- sizeof buf); \& if (nbd_pread (nbd, buf, sizeof buf, \& offset, 0) == \-1) { \& fprintf (stderr, "%s\en", nbd_get_error ()); \& exit (EXIT_FAILURE); \& } \& \& offset = rand () % (exportsize \- sizeof buf); \& if (nbd_pwrite (nbd, buf, sizeof buf, \& offset, 0) == \-1) { \& fprintf (stderr, "%s\en", nbd_get_error ()); \& exit (EXIT_FAILURE); \& } \& } \& \& /* Sends a graceful shutdown to the server. */ \& if (nbd_shutdown (nbd, 0) == \-1) { \& fprintf (stderr, "%s\en", nbd_get_error ()); \& exit (EXIT_FAILURE); \& } \& \& nbd_close (nbd); \& \& exit (EXIT_SUCCESS); \& } .Ve .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBnbd_aio_pwrite\fR\|(3), \&\fBnbd_can_fua\fR\|(3), \&\fBnbd_create\fR\|(3), \&\fBnbd_get_block_size\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 (C) 2019\-2020 Red Hat Inc. .SH "LICENSE" .IX Header "LICENSE" This library is free software; you can redistribute it and/or modify it under the terms of the \s-1GNU\s0 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 \s-1WITHOUT ANY WARRANTY\s0; without even the implied warranty of \&\s-1MERCHANTABILITY\s0 or \s-1FITNESS FOR A PARTICULAR PURPOSE.\s0 See the \s-1GNU\s0 Lesser General Public License for more details. .PP You should have received a copy of the \s-1GNU\s0 Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, \s-1MA 02110\-1301 USA\s0