Index: head/lib/libc/sys/sendfile.2
===================================================================
--- head/lib/libc/sys/sendfile.2	(revision 343443)
+++ head/lib/libc/sys/sendfile.2	(revision 343444)
@@ -1,405 +1,416 @@
 .\" Copyright (c) 2003, David G. Lawrence
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 .\"
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 .\" modification, are permitted provided that the following conditions
 .\" are met:
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 .\"    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
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 .\" 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
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 .\" SUCH DAMAGE.
 .\"
 .\" $FreeBSD$
 .\"
-.Dd October 12, 2018
+.Dd January 25, 2019
 .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 or shared memory object 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 least significant 16 bits of
 .Fa flags
 argument is a bitmap of these values:
-.Bl -tag -offset indent
+.Bl -tag -offset indent -width "SF_USER_READAHEAD"
 .It Dv SF_NODISKIO
 This flag causes
 .Nm
 to return
 .Er EBUSY
 instead of blocking when a busy page is encountered.
 This rare situation can happen if some other process is now working
 with the same region of the file.
 It is advised to retry the operation after a short period.
 .Pp
 Note that in older
 .Fx
 versions the
 .Dv SF_NODISKIO
 had slightly different notion.
 The flag prevented
 .Nm
 to run I/O operations in case if an invalid (not cached) page is encountered,
 thus avoiding blocking on I/O.
 Starting with
 .Fx 11
 .Nm
 sending files off the
 .Xr ffs 7
 filesystem does not block on I/O
 (see
 .Sx IMPLEMENTATION NOTES
 ), so the condition no longer applies.
 However, it is safe if an application utilizes
 .Dv SF_NODISKIO
 and on
 .Er EBUSY
 performs the same action as it did in
 older
 .Fx
 versions, e.g.,
 .Xr aio_read 2 ,
 .Xr read 2
 or
 .Nm
 in a different context.
 .It Dv SF_NOCACHE
 The data sent to socket will not be cached by the virtual memory system,
 and will be freed directly to the pool of free pages.
 .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.
 .It Dv SF_USER_READAHEAD
 .Nm
 has some internal heuristics to do readahead when sending data.
 This flag forces
 .Nm
 to override any heuristically calculated readahead and use exactly the
 application specified readahead.
 See
 .Sx SETTING READAHEAD
 for more details on readahead.
 .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 SETTING READAHEAD
 .Nm
 uses internal heuristics based on request size and file system layout
 to do readahead.
 Additionally application may request extra readahead.
 The most significant 16 bits of
 .Fa flags
 specify amount of pages that
 .Nm
 may read ahead when reading the file.
 A macro
 .Fn SF_FLAGS
 is provided to combine readahead amount and flags.
 An example showing specifying readahead of 16 pages and
 .Dv SF_NOCACHE
 flag:
 .Pp
 .Bd -literal -offset indent -compact
 	SF_FLAGS(16, SF_NOCACHE)
 .Ed
 .Pp
 .Nm
 will use either application specified readahead or internally calculated,
 whichever is bigger.
 Setting flag
 .Dv SF_USER_READAHEAD
 would turn off any heuristics and set maximum possible readahead length to
 the number of pages specified via flags.
 .Sh IMPLEMENTATION NOTES
 The
 .Fx
 implementation of
 .Fn sendfile
 does not block on disk I/O when it sends a file off the
 .Xr ffs 7
 filesystem.
 The syscall returns success before the actual I/O completes, and data
 is put into the socket later unattended.
 However, the order of data in the socket is preserved, so it is safe
 to do further writes to the socket.
 .Pp
 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
 A busy page was encountered and
 .Dv SF_NODISKIO
 had been specified.
 Partial data may have been sent.
 .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 ENOTCAPABLE
 The
 .Fa fd
 or the
 .Fa s
 argument has insufficient rights.
 .It Bq Er ENOBUFS
 The system was unable to allocate an internal buffer.
 .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 .
 In
 .Fx 10
 support for sending shared memory descriptors had been introduced.
 In
 .Fx 11
 a non-blocking implementation had been introduced.
 .Sh AUTHORS
 The initial implementation of
 .Fn sendfile
 system call
 and this manual page were written by
 .An David G. Lawrence Aq Mt dg@dglawrence.com .
 The
 .Fx 11
 implementation was written by
 .An Gleb Smirnoff Aq Mt glebius@FreeBSD.org .
+.Sh BUGS
+The
+.Fn sendfile
+system call will not fail, i.e., return
+.Dv -1
+and set
+.Va errno
+to
+.Er EFAULT ,
+if provided an invalid address for
+.Fa sbytes .