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Diffstat (limited to 'lib/libc/sys/sendfile.2')
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diff --git a/lib/libc/sys/sendfile.2 b/lib/libc/sys/sendfile.2 new file mode 100644 index 0000000..d9f8cab --- /dev/null +++ b/lib/libc/sys/sendfile.2 @@ -0,0 +1,316 @@ +.\" Copyright (c) 2003, David G. Lawrence +.\" All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice unmodified, this list of conditions, and the following +.\" disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" $FreeBSD$ +.\" +.Dd January 7, 2010 +.Dt SENDFILE 2 +.Os +.Sh NAME +.Nm sendfile +.Nd send a file to a socket +.Sh LIBRARY +.Lb libc +.Sh SYNOPSIS +.In sys/types.h +.In sys/socket.h +.In sys/uio.h +.Ft int +.Fo sendfile +.Fa "int fd" "int s" "off_t offset" "size_t nbytes" +.Fa "struct sf_hdtr *hdtr" "off_t *sbytes" "int flags" +.Fc +.Sh DESCRIPTION +The +.Fn sendfile +system call +sends a regular file specified by descriptor +.Fa fd +out a stream socket specified by descriptor +.Fa s . +.Pp +The +.Fa offset +argument specifies where to begin in the file. +Should +.Fa offset +fall beyond the end of file, the system will return +success and report 0 bytes sent as described below. +The +.Fa nbytes +argument specifies how many bytes of the file should be sent, with 0 having the special +meaning of send until the end of file has been reached. +.Pp +An optional header and/or trailer can be sent before and after the file data by specifying +a pointer to a +.Vt "struct sf_hdtr" , +which has the following structure: +.Pp +.Bd -literal -offset indent -compact +struct sf_hdtr { + struct iovec *headers; /* pointer to header iovecs */ + int hdr_cnt; /* number of header iovecs */ + struct iovec *trailers; /* pointer to trailer iovecs */ + int trl_cnt; /* number of trailer iovecs */ +}; +.Ed +.Pp +The +.Fa headers +and +.Fa trailers +pointers, if +.Pf non- Dv NULL , +point to arrays of +.Vt "struct iovec" +structures. +See the +.Fn writev +system call for information on the iovec structure. +The number of iovecs in these +arrays is specified by +.Fa hdr_cnt +and +.Fa trl_cnt . +.Pp +If +.Pf non- Dv NULL , +the system will write the total number of bytes sent on the socket to the +variable pointed to by +.Fa sbytes . +.Pp +The +.Fa flags +argument is a bitmap of these values: +.Bl -item -offset indent +.It +.Dv SF_NODISKIO . +This flag causes any +.Fn sendfile +call which would block on disk I/O to instead +return +.Er EBUSY . +Busy servers may benefit by transferring requests that would +block to a separate I/O worker thread. +.It +.Dv SF_MNOWAIT . +Do not wait for some kernel resource to become available, +in particular, +.Vt mbuf +and +.Vt sf_buf . +The flag does not make the +.Fn sendfile +syscall truly non-blocking, since other resources are still allocated +in a blocking fashion. +.It +.Dv SF_SYNC . +.Nm +sleeps until the network stack no longer references the VM pages +of the file, making subsequent modifications to it safe. +Please note that this is not a guarantee that the data has actually +been sent. +.El +.Pp +When using a socket marked for non-blocking I/O, +.Fn sendfile +may send fewer bytes than requested. +In this case, the number of bytes successfully +written is returned in +.Fa *sbytes +(if specified), +and the error +.Er EAGAIN +is returned. +.Sh IMPLEMENTATION NOTES +The +.Fx +implementation of +.Fn sendfile +is "zero-copy", meaning that it has been optimized so that copying of the file data is avoided. +.Sh TUNING +On some architectures, this system call internally uses a special +.Fn sendfile +buffer +.Pq Vt "struct sf_buf" +to handle sending file data to the client. +If the sending socket is +blocking, and there are not enough +.Fn sendfile +buffers available, +.Fn sendfile +will block and report a state of +.Dq Li sfbufa . +If the sending socket is non-blocking and there are not enough +.Fn sendfile +buffers available, the call will block and wait for the +necessary buffers to become available before finishing the call. +.Pp +The number of +.Vt sf_buf Ns 's +allocated should be proportional to the number of nmbclusters used to +send data to a client via +.Fn sendfile . +Tune accordingly to avoid blocking! +Busy installations that make extensive use of +.Fn sendfile +may want to increase these values to be inline with their +.Va kern.ipc.nmbclusters +(see +.Xr tuning 7 +for details). +.Pp +The number of +.Fn sendfile +buffers available is determined at boot time by either the +.Va kern.ipc.nsfbufs +.Xr loader.conf 5 +variable or the +.Dv NSFBUFS +kernel configuration tunable. +The number of +.Fn sendfile +buffers scales with +.Va kern.maxusers . +The +.Va kern.ipc.nsfbufsused +and +.Va kern.ipc.nsfbufspeak +read-only +.Xr sysctl 8 +variables show current and peak +.Fn sendfile +buffers usage respectively. +These values may also be viewed through +.Nm netstat Fl m . +.Pp +If a value of zero is reported for +.Va kern.ipc.nsfbufs , +your architecture does not need to use +.Fn sendfile +buffers because their task can be efficiently performed +by the generic virtual memory structures. +.Sh RETURN VALUES +.Rv -std sendfile +.Sh ERRORS +.Bl -tag -width Er +.It Bq Er EAGAIN +The socket is marked for non-blocking I/O and not all data was sent due to +the socket buffer being filled. +If specified, the number of bytes successfully sent will be returned in +.Fa *sbytes . +.It Bq Er EBADF +The +.Fa fd +argument +is not a valid file descriptor. +.It Bq Er EBADF +The +.Fa s +argument +is not a valid socket descriptor. +.It Bq Er EBUSY +Completing the entire transfer would have required disk I/O, so +it was aborted. +Partial data may have been sent. +(This error can only occur when +.Dv SF_NODISKIO +is specified.) +.It Bq Er EFAULT +An invalid address was specified for an argument. +.It Bq Er EINTR +A signal interrupted +.Fn sendfile +before it could be completed. +If specified, the number +of bytes successfully sent will be returned in +.Fa *sbytes . +.It Bq Er EINVAL +The +.Fa fd +argument +is not a regular file. +.It Bq Er EINVAL +The +.Fa s +argument +is not a SOCK_STREAM type socket. +.It Bq Er EINVAL +The +.Fa offset +argument +is negative. +.It Bq Er EIO +An error occurred while reading from +.Fa fd . +.It Bq Er ENOTCONN +The +.Fa s +argument +points to an unconnected socket. +.It Bq Er ENOTSOCK +The +.Fa s +argument +is not a socket. +.It Bq Er EOPNOTSUPP +The file system for descriptor +.Fa fd +does not support +.Fn sendfile . +.It Bq Er EPIPE +The socket peer has closed the connection. +.El +.Sh SEE ALSO +.Xr netstat 1 , +.Xr open 2 , +.Xr send 2 , +.Xr socket 2 , +.Xr writev 2 , +.Xr tuning 7 +.Rs +.%A K. Elmeleegy +.%A A. Chanda +.%A A. L. Cox +.%A W. Zwaenepoel +.%T A Portable Kernel Abstraction for Low-Overhead Ephemeral Mapping Management +.%J The Proceedings of the 2005 USENIX Annual Technical Conference +.%P pp 223-236 +.%D 2005 +.Re +.Sh HISTORY +The +.Fn sendfile +system call +first appeared in +.Fx 3.0 . +This manual page first appeared in +.Fx 3.1 . +.Sh AUTHORS +The +.Fn sendfile +system call +and this manual page were written by +.An David G. Lawrence Aq dg@dglawrence.com . |