The uiomove() function copies nbytes of data to or from the space defined by the uio structure (described in uio(9S)) and the driver.
The uio_segflg member of the uio(9S)
structure determines the type of space to or from which the transfer is being made. If it is set to UIO_SYSSPACE, the data transfer is between addresses in
the kernel. If it is set to UIO_USERSPACE, the transfer is between a user program and kernel space.
rwflag indicates the direction of the transfer. If UIO_READ is set, the data will be transferred from address
to the buffer(s) described by uio_p. If UIO_WRITE is set, the data will be transferred from the buffer(s) described by uio_p
to address.
In addition to moving the data, uiomove() adds the number of bytes moved to the iov_base member of the iovec(9S) structure, decreases the iov_len member, increases the uio_offset member of the
uio(9S) structure, and decreases the uio_resid
member.
This function automatically handles page faults. nbytes does not have to be word-aligned.
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