| Rev | Author | # | Line |
|---|---|---|---|
| 1 | perry | 1 | sendfile - transfer data between file descriptors |
| 2 | !!SYNOPSIS | ||
| 3 | |||
| 4 | |||
| 2 | PerryLorier | 5 | __#include <sys/sendfile.h>__ |
| 1 | perry | 6 | |
| 2 | PerryLorier | 7 | __ssize_t sendfile(int__ ''out_fd''__, int__ ''in_fd''__, off_t *__''offset''__, size_t__ ''count''__)__ |
| 1 | perry | 8 | |
| 9 | !!DESCRIPTION | ||
| 2 | PerryLorier | 10 | 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 |
| 11 | 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 | ||
| 12 | which sendfile(2) will start reading data. When sendfile(2) 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. | ||
| 1 | perry | 13 | |
| 2 | PerryLorier | 14 | Because this copying is done within the kernel, sendfile(2) does not need to spend time transferring data to and from user space. |
| 1 | perry | 15 | |
| 16 | !!NOTES | ||
| 2 | PerryLorier | 17 | Sendfile does not modify the current file pointer of ''in_fd'', but does for ''out_fd''. |
| 1 | perry | 18 | |
| 2 | PerryLorier | 19 | 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. |
| 1 | perry | 20 | |
| 2 | PerryLorier | 21 | Presently the descriptor from which data is read cannot correspond to a socket, it must correspond to a file which supports mmap(2)-like operations. |
| 1 | perry | 22 | |
| 23 | !!RETURN VALUE | ||
| 2 | PerryLorier | 24 | 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. |
| 1 | perry | 25 | |
| 26 | !!ERRORS | ||
| 2 | PerryLorier | 27 | ;[EBADF]: The input file was not opened for reading or the output file was not opened for writing. |
| 28 | ;[EINVAL]: Descriptor is not valid or locked. | ||
| 29 | ;[ENOMEM]: Insufficient memory to read from ''in_fd''. | ||
| 30 | ;[EIO]: Unspecified error while reading from ''in_fd''. | ||
| 1 | perry | 31 | |
| 32 | !!VERSIONS | ||
| 2 | PerryLorier | 33 | sendfile(2) is a new feature in Linux 2.2. The include file <sys/sendfile.h> is present since glibc 2.1. |
| 1 | perry | 34 | |
| 2 | PerryLorier | 35 | Other Unixes often implement sendfile(2) with different semantics and prototypes. It should not be used in portable programs. |
| 1 | perry | 36 | |
| 37 | !!SEE ALSO | ||
| 38 | socket(2), open(2) |
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