Originální popis anglicky:
sendfile - transfer data between file descriptors
Návod, kniha: Linux Programmer's Manual
#include <sys/sendfile.h>
ssize_t sendfile(int out_fd, int in_fd, off_t
*offset, size_t count);
This call copies data between one file descriptor and another. Either or both of
these file descriptors may refer to a socket (but see below).
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() 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.
Because this copying is done within the kernel,
sendfile() does not need
to spend time transferring data to and from user space.
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.
Presently the descriptor from which data is read cannot correspond to a socket,
it must correspond to a file which supports mmap()-like operations.
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.
- EAGAIN
- Non-blocking I/O has been selected using O_NONBLOCK
and the write would block.
- EBADF
- The input file was not opened for reading or the output
file was not opened for writing.
- EFAULT
- Bad address.
- EINVAL
- Descriptor is not valid or locked.
- EIO
- Unspecified error while reading from in_fd.
- ENOMEM
- Insufficient memory to read from in_fd.
sendfile is a new feature in Linux 2.2. The include file
<sys/sendfile.h> is present since glibc2.1.
Other Unixes often implement
sendfile with different semantics and
prototypes. It should not be used in portable programs.
open(2),
socket(2)
