1 .\" Copyright (c) 2003, David G. Lawrence
2 .\" All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice unmodified, this list of conditions, and the following
10 .\" 2. Redistributions in binary form must reproduce the above copyright
11 .\" notice, this list of conditions and the following disclaimer in the
12 .\" documentation and/or other materials provided with the distribution.
14 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 .Nd send a file to a socket
42 .Fa "int fd" "int s" "off_t offset" "size_t nbytes"
43 .Fa "struct sf_hdtr *hdtr" "off_t *sbytes" "int flags"
49 sends a regular file or shared memory object specified by descriptor
51 out a stream socket specified by descriptor
56 argument specifies where to begin in the file.
59 fall beyond the end of file, the system will return
60 success and report 0 bytes sent as described below.
63 argument specifies how many bytes of the file should be sent, with 0 having the special
64 meaning of send until the end of file has been reached.
66 An optional header and/or trailer can be sent before and after the file data by specifying
68 .Vt "struct sf_hdtr" ,
69 which has the following structure:
71 .Bd -literal -offset indent -compact
73 struct iovec *headers; /* pointer to header iovecs */
74 int hdr_cnt; /* number of header iovecs */
75 struct iovec *trailers; /* pointer to trailer iovecs */
76 int trl_cnt; /* number of trailer iovecs */
91 system call for information on the iovec structure.
92 The number of iovecs in these
93 arrays is specified by
100 the system will write the total number of bytes sent on the socket to the
101 variable pointed to by
104 The least significant 16 bits of
106 argument is a bitmap of these values:
107 .Bl -tag -offset indent
113 instead of blocking when a busy page is encountered.
114 This rare situation can happen if some other process is now working
115 with the same region of the file.
116 It is advised to retry the operation after a short period.
122 had slightly different notion.
125 to run I/O operations in case if an invalid (not cached) page is encountered,
126 thus avoiding blocking on I/O.
130 sending files off the
132 filesystem doesn't block on I/O
134 .Sx IMPLEMENTATION NOTES
135 ), so the condition no longer applies.
136 However, it is safe if an application utilizes
140 performs the same action as it did in
148 in a different context.
150 The data sent to socket will not be cached by the virtual memory system,
151 and will be freed directly to the pool of free pages.
154 sleeps until the network stack no longer references the VM pages
155 of the file, making subsequent modifications to it safe.
156 Please note that this is not a guarantee that the data has actually
160 The most significant 16 bits of
162 specify amount of pages that
164 may read ahead when reading the file.
167 is provided to combine readahead amount and flags.
168 Example shows specifing readahead of 16 pages and
172 .Bd -literal -offset indent -compact
173 SF_FLAGS(16, SF_NOCACHE)
176 When using a socket marked for non-blocking I/O,
178 may send fewer bytes than requested.
179 In this case, the number of bytes successfully
180 written is returned in
186 .Sh IMPLEMENTATION NOTES
191 doesn't block on disk I/O when it sends a file off the
194 The syscall returns success before the actual I/O completes, and data
195 is put into the socket later unattended.
196 However, the order of data in the socket is preserved, so it is safe
197 to do further writes to the socket.
203 is "zero-copy", meaning that it has been optimized so that copying of the file data is avoided.
205 On some architectures, this system call internally uses a special
208 .Pq Vt "struct sf_buf"
209 to handle sending file data to the client.
210 If the sending socket is
211 blocking, and there are not enough
215 will block and report a state of
217 If the sending socket is non-blocking and there are not enough
219 buffers available, the call will block and wait for the
220 necessary buffers to become available before finishing the call.
224 allocated should be proportional to the number of nmbclusters used to
225 send data to a client via
227 Tune accordingly to avoid blocking!
228 Busy installations that make extensive use of
230 may want to increase these values to be inline with their
231 .Va kern.ipc.nmbclusters
238 buffers available is determined at boot time by either the
243 kernel configuration tunable.
249 .Va kern.ipc.nsfbufsused
251 .Va kern.ipc.nsfbufspeak
254 variables show current and peak
256 buffers usage respectively.
257 These values may also be viewed through
260 If a value of zero is reported for
261 .Va kern.ipc.nsfbufs ,
262 your architecture does not need to use
264 buffers because their task can be efficiently performed
265 by the generic virtual memory structures.
271 The socket is marked for non-blocking I/O and not all data was sent due to
272 the socket buffer being filled.
273 If specified, the number of bytes successfully sent will be returned in
279 is not a valid file descriptor.
284 is not a valid socket descriptor.
286 A busy page was encountered and
289 Partial data may have been sent.
291 An invalid address was specified for an argument.
295 before it could be completed.
296 If specified, the number
297 of bytes successfully sent will be returned in
303 is not a regular file.
308 is not a SOCK_STREAM type socket.
315 An error occurred while reading from
318 The system was unable to allocate an internal buffer.
323 points to an unconnected socket.
330 The file system for descriptor
335 The socket peer has closed the connection.
349 .%T A Portable Kernel Abstraction for Low-Overhead Ephemeral Mapping Management
350 .%J The Proceedings of the 2005 USENIX Annual Technical Conference
360 This manual page first appeared in
364 support for sending shared memory descriptors had been introduced.
367 a non-blocking implementation had been introduced.
369 The initial implementation of
372 and this manual page were written by
373 .An David G. Lawrence Aq Mt dg@dglawrence.com .
376 implementation was written by
377 .An Gleb Smirnoff Aq Mt glebius@FreeBSD.org .