SENDFILEV(3EXT) Extended Library Functions SENDFILEV(3EXT)


NAME


sendfilev - send a file

SYNOPSIS


cc [ flag... ] file... -lsendfile [ library... ]
#include <sys/sendfile.h>

ssize_t sendfilev(int fildes, const struct sendfilevec *vec,
int sfvcnt, size_t *xferred);


PARAMETERS


The sendfilev() function supports the following parameters:

fildes
A file descriptor to a regular file or to a AF_NCA, AF_INET,
or AF_INET6 family type SOCK_STREAM socket that is open for
writing. For AF_NCA, the protocol type should be zero.


vec
An array of SENDFILEVEC_T, as defined in the sendfilevec
structure below.


sfvcnt
The number of members in vec.


xferred
The total number of bytes written to out_fd.


DESCRIPTION


The sendfilev() function attempts to write data from the sfvcnt buffers
specified by the members of vec array: vec[0], vec[1], ... ,
vec[sfvcnt-1]. The fildes argument is a file descriptor to a regular file
or to an AF_NCA, AF_INET, or AF_INET6 family type SOCK_STREAM socket that
is open for writing.


This function is analogous to writev(2), but can read from both buffers
and file descriptors. Unlike writev(), in the case of multiple writers to
a file the effect of sendfilev() is not necessarily atomic; the writes
may be interleaved. Application-specific synchronization methods must be
employed if this causes problems.


The following is the sendfilevec structure:

typedef struct sendfilevec {
int sfv_fd; /* input fd */
uint_t sfv_flag; /* Flags. see below */
off_t sfv_off; /* offset to start reading from */
size_t sfv_len; /* amount of data */
} sendfilevec_t;

#define SFV_FD_SELF (-2)


To send a file, open the file for reading and point sfv_fd to the file
descriptor returned as a result. See open(2). sfv_off should contain the
offset within the file. sfv_len should have the length of the file to be
transferred.


The xferred argument is updated to record the total number of bytes
written to out_fd.


The sfv_flag field is reserved and should be set to zero.


To send data directly from the address space of the process, set sfv_fd
to SFV_FD_SELF. sfv_off should point to the data, with sfv_len containing
the length of the buffer.

RETURN VALUES


Upon successful completion, the sendfilev() function returns total number
of bytes written to out_fd. Otherwise, it returns -1, and errno is set to
indicate the error. The xferred argument contains the amount of data
successfully transferred, which can be used to discover the error vector.

ERRORS


EACCES
The process does not have appropriate privileges or one
of the files pointed by sfv_fd does not have appropriate
permissions.


EAFNOSUPPORT
The implementation does not support the specified address
family for socket.


EAGAIN
Mandatory file or record locking is set on either the
file descriptor or output file descriptor if it points at
regular files. O_NDELAY or O_NONBLOCK is set, and there
is a blocking record lock. An attempt has been made to
write to a stream that cannot accept data with the
O_NDELAY or the O_NONBLOCK flag set.


EBADF
The fildes argument is not a valid descriptor open for
writing or an sfv_fd is invalid or not open for reading.


EFAULT
The vec argument points to an illegal address.

The xferred argument points to an illegal address.


EINTR
A signal was caught during the write operation and no
data was transferred.


EINVAL
The sfvcnt argument was less than or equal to 0. One of
the sfv_len values in vec array was less than or equal to
0, or greater than the file size. An sfv_fd is not
seekable.

Fewer bytes were transferred than were requested.


EIO
An I/O error occurred while accessing the file system.


EPIPE
The fildes argument is a socket that has been shut down
for writing. The SIGPIPE signal is generated to the
calling thread. The process dies unless special
provisions were taken to catch or ignore the signal.


EPROTOTYPE
The socket type is not supported.


USAGE


The sendfilev() function has a transitional interface for 64-bit file
offsets. See lf64(7).

EXAMPLES


The following example sends 2 vectors, one of HEADER data and a file of
length 100 over sockfd. sockfd is in a connected state, that is,
socket(), accept(), and bind() operation are complete.

#include <sys/sendfile.h>
.
.
.
int
main (int argc, char *argv[]){
int sockfd;
ssize_t ret;
size_t xfer;
struct sendfilevec vec[2];
.
.
.
vec[0].sfv_fd = SFV_FD_SELF;
vec[0].sfv_flag = 0;
vec[0].sfv_off = "HEADER_DATA";
vec[0].sfv_len = strlen("HEADER_DATA");
vec[1].sfv_fd = open("input_file",.... );
vec[1].sfv_flag = 0;
vec[1].sfv_off = 0;
vec[1].sfv_len = 100;

ret = sendfilev(sockfd, vec, 2, &xfer);
.
.
.
}


ATTRIBUTES


See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Committed |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO


open(2), writev(2), sendfile(3EXT), libsendfile(3LIB), socket(3SOCKET),
attributes(7)


November 26, 2017 SENDFILEV(3EXT)