mmap() improvements from Martin Pool

man2/sendfile.2

@@ -10,13 +10,16 @@
 .\"	updated description of in_fd and out_fd for 2.6
 .\"	Various wording and formatting changes
 .\"
+.\" 2005-03-31 Martin Pool <mbp@sourcefrog.net> mmap() improvements
+.\"
 .TH SENDFILE 2 2004-12-17 "Linux Man Page" "Linux Programmer's Manual" 
 .SH NAME
 sendfile \- transfer data between file descriptors
 .SH SYNOPSIS
 .B #include <sys/sendfile.h>
 .sp
-.BI "ssize_t sendfile(int" " out_fd" ", int" " in_fd" ", off_t *" offset ", size_t" " count" );
+.BI "ssize_t sendfile(int" " out_fd" ", int" " in_fd" ", off_t *" \
+                      offset ", size_t" " count" );
 .\" The below is too ugly. Comments about glibc versions belong
 .\" in the notes, not in the header.
 .\"
@@ -32,7 +35,8 @@ sendfile \- transfer data between file descriptors
 .\" .br
 .\" .B /* No system prototype before glibc 2.1. */ 
 .\" .br
-.\" .BI "ssize_t sendfile(int" " out_fd" ", int" " in_fd" ", off_t *" offset ", size_t" " count" )
+.\" .BI "ssize_t sendfile(int" " out_fd" ", int" " in_fd" ", off_t *" \
+.\"                       offset ", size_t" " count" )
 .\" .br
 .\" .B #endif
 .\"
@@ -76,6 +80,12 @@ must correspond to a file which supports mmap()-like operations
 and
 .I out_fd
 must refer to a socket.
+
+Applications may wish to fall back to
+.BR read (2)/ write (2)
+in the case where
+.BR sendfile ()
+fails with EINVAL or ENOSYS.
 .SH NOTES
 If you plan to use sendfile for sending files to a TCP socket, but need
 to send some header data in front of the file contents, you will find
@@ -111,7 +121,9 @@ was not opened for writing.
 Bad address.
 .TP
 .B EINVAL
-Descriptor is not valid or locked.
+Descriptor is not valid or locked, or an mmap()-like
+operation is not available for
+.IR in_fd .
 .TP
 .B EIO
 Unspecified error while reading from
@@ -131,4 +143,5 @@ with different semantics and prototypes. It should
 not be used in portable programs.
 .SH "SEE ALSO"
 .BR open (2),
+.BR mmap (2),
 .BR socket (2)