SENDFILE

NAME
SYNOPSIS
DESCRIPTION
NOTES
RETURN VALUE
ERRORS
VERSIONS
SEE ALSO

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)