uiomove(9) - NetBSD Manual Pages

UIOMOVE(9)             NetBSD Kernel Developer's Manual             UIOMOVE(9)


NAME

     uiomove -- move data described by a struct uio


SYNOPSIS

     #include <sys/systm.h>

     int
     uiomove(void *buf, size_t n, struct uio *uio);

     int
     uiopeek(void *buf, size_t n, struct uio *uio);

     void
     uioskip(void *buf, size_t n, struct uio *uio);


DESCRIPTION

     The uiomove() function copies up to n bytes between the kernel-space
     address pointed to by buf and the addresses described by uio, which may
     be in user-space or kernel-space.

     The uio argument is a pointer to a struct uio as defined by <sys/uio.h>:

           struct uio {
                   struct  iovec *uio_iov;
                   int     uio_iovcnt;
                   off_t   uio_offset;
                   size_t  uio_resid;
                   enum    uio_rw uio_rw;
                   struct  vmspace *uio_vmspace;
           };

     A struct uio typically describes data in motion.  Several of the fields
     described below reflect that expectation.

     uio_iov       Pointer to array of I/O vectors to be processed.  The
                   struct iovec is defined to be:

                         struct iovec {
                                 void    *iov_base;
                                 size_t   iov_len;
                         };

                   The members in the struct iovec should only be initialized.
                   These are:

                         iov_base    The address for a range of memory to or
                                     from which data is transferred.

                         iov_len     The number of bytes of data to be trans-
                                     ferred to or from the range of memory
                                     starting at iov_base.

     uio_iovcnt    The number of I/O vectors in the uio_iov array.

     uio_offset    An offset into the corresponding object.

     uio_resid     The amount of space described by the structure; notionally,
                   the amount of data remaining to be transferred.

     uio_rw        A flag indicating whether data should be read into the
                   space (UIO_READ) or written from the space (UIO_WRITE).

     uio_vmspace   A pointer to the address space which is being transferred
                   to or from.

     The value of uio->uio_rw controls whether uiomove() copies data from buf
     to uio or vice versa.

     The lesser of n or uio->uio_resid bytes are copied.

     uiomove() changes fields of the structure pointed to by uio, such that
     uio->uio_resid is decremented by the amount of data moved,
     uio->uio_offset is incremented by the same amount, and the array of
     iovecs is adjusted to point that much farther into the region described.
     This allows multiple calls to uiomove() to easily be used to fill or
     drain the region of data.

     The uiopeek() function copies up to n bytes of data without updating uio;
     the uioskip() function updates uio without copying any data, and is guar-
     anteed never to sleep or fault even if the buffers are in userspace and
     memory access via uiomove() or uiopeek() would trigger paging.  A suc-
     cessful uiomove(buf, n, uio) call is equivalent to a successful
     uiopeek(buf, n, uio) followed by uioskip(n, uio).


RETURN VALUES

     Upon successful completion, uiomove() and uiopeek() return 0.  If a bad
     address is encountered, EFAULT is returned.


SEE ALSO

     copy(9), ufetch(9), ustore(9)

NetBSD 10.99                      May 9, 2023                     NetBSD 10.99