DOFILEREAD(9)

DOFILEREAD(9) | Kernel Developer's Manual | DOFILEREAD(9)

# 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.

# SEE ALSO

file(9)

December 20, 2005 | NetBSD 10.1