SENDFILE
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
sendfile(2)
will start reading data. When
sendfile
returns, this variable
will be set to the offset of the byte following 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 written 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)