NAME
dofileread,
dofilereadv, dofilewrite,
dofilewritev —
high-level file operations
SYNOPSIS
#include
<sys/file.h>
int
dofileread(struct
lwp *l, int fd,
struct file *fp,
void *buf,
size_t nbyte,
off_t *offset,
int flags,
register_t *retval);
int
dofilewrite(struct
lwp *l, int fd,
struct file *fp,
const void *buf,
size_t nbyte,
off_t *offset,
int flags,
register_t *retval);
int
dofilereadv(struct
lwp *l, int fd,
struct file *fp,
const struct iovec *iovp,
int iovcnt,
off_t *offset,
int flags,
register_t *retval);
int
dofilewritev(struct
lwp *l, int fd,
struct file *fp,
const struct iovec *iovp,
int iovcnt,
off_t *offset,
int flags,
register_t *retval);
DESCRIPTION
The functions implement the underlying functionality of the read(2), write(2), readv(2), and writev(2) system calls. They are also used throughout the kernel as high-level access routines for file I/O.The
dofileread()
function attempts to read nbytes of data from the
object referenced by file entry fp into the buffer
pointed to by buf. The
dofilewrite()
function attempts to write nbytes of data to the
object referenced by file entry fp from the buffer
pointed to by buf.
The
dofilereadv()
and
dofilewritev()
functions perform the same operations, but scatter the data with the
iovcnt buffers specified by the members of the
iov array.
The offset of the file operations is explicitly specified by *offset. The new file offset after the file operation is returned in *offset. If the FOF_UPDATE_OFFSET flag is specified in the flags argument, the file offset in the file entry fp is updated to reflect the new file offset, otherwise it remains unchanged after the operation.
The file descriptor fd is largely unused except for use by the ktrace framework for reporting to userlevel the process's file descriptor.
Upon successful completion the number of bytes which were transferred is returned in *retval.
RETURN VALUES
Upon successful completion zero is returned, otherwise an appropriate error is returned.
CODE REFERENCES
The framework for these file operations is implemented within the file sys/kern/sys_generic.c.