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NetBSD 6.1.5 - man page for dofileread (netbsd section 9)

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DOFILEREAD(9)			  BSD 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 rou-
     tines 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 report-
     ing 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)

BSD					December 20, 2005				      BSD
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