sendfile(2)

NAME

       sendfile - transfer data between file descriptors

SYNOPSIS

       #include <unistd.h>

       ssize_t  sendfile(int  out_fd,  int  in_fd, off_t *offset,
       size_t count)

DESCRIPTION

       This call copies data  between  one  file  descriptor  and
       another.   Either  or  both  of these file descriptors may
       refer to a socket.  in_fd  should  be  a  file  descriptor
       opened  for  reading  and  out_fd  should  be a descriptor
       opened for writing.  offset is a  pointer  to  a  variable
       holding  the  input file pointer position from which send­
       file(2) will start reading data.  When  sendfile  returns,
       this  variable  will be set to the offset of the byte fol­
       lowing the last byte that was read.  count is  the  number
       of bytes to copy between file descriptors.

NOTES

       Sendfile  does  not  modify  the  current  file pointer of
       in_fd, but does for out_fd.

       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, please see the TCP_CORK option in tcp(7) to
       minimize the number of packets and to tune performance.

RETURN VALUE

       If  the transfer was successful, the number of bytes writ­
       ten to out_fd is returned.  On error, -1 is returned,  and
       errno is set appropriately.

ERRORS

       EBADF  The  input  file  was not opened for reading or the
              output file was not opened for writing.

       EINVAL Descriptor is not valid or locked.

       ENOMEM Insufficient memory to read from in_fd.

       EIO    Unspecified error while reading from in_fd.

VERSIONS

       sendfile is a new feature in Linux 2.2.

       Other  Unixes  often  implement  sendfile  with  different
       semantics  and  prototypes.  It  should  not  be  used  in
       portable programs.

SEE ALSO

       socket(2), open(2)