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uiomove(9) [netbsd man page]

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

uiomove -- move data described by a struct uio SYNOPSIS
#include <sys/systm.h> int uiomove(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 transferred 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. RETURN VALUES
Upon successful completion, uiomove() returns 0. If a bad address is encountered, EFAULT is returned. SEE ALSO
copy(9), fetch(9), store(9) BSD
April 26, 2010 BSD

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UIO(9)							   BSD Kernel Developer's Manual						    UIO(9)

uio, uiomove -- device driver I/O routines SYNOPSIS
#include <sys/types.h> #include <sys/uio.h> struct uio { struct iovec *uio_iov; /* scatter/gather list */ int uio_iovcnt; /* length of scatter/gather list */ off_t uio_offset; /* offset in target object */ ssize_t uio_resid; /* remaining bytes to copy */ enum uio_seg uio_segflg; /* address space */ enum uio_rw uio_rw; /* operation */ struct thread *uio_td; /* owner */ }; int uiomove(void *buf, int howmuch, struct uio *uiop); DESCRIPTION
The function uiomove() is used to handle transfer of data between buffers and I/O vectors that might possibly also cross the user/kernel space boundary. As a result of any read(2), write(2), readv(2), or writev(2) system call that is being passed to a character-device driver, the appropriate driver d_read or d_write entry will be called with a pointer to a struct uio being passed. The transfer request is encoded in this struc- ture. The driver itself should use uiomove() to get at the data in this structure. The fields in the uio structure are: uio_iov The array of I/O vectors to be processed. In the case of scatter/gather I/O, this will be more than one vector. uio_iovcnt The number of I/O vectors present. uio_offset The offset into the device. uio_resid The remaining number of bytes to process, updated after transfer. uio_segflg One of the following flags: UIO_USERSPACE The I/O vector points into a process's address space. UIO_SYSSPACE The I/O vector points into the kernel address space. UIO_NOCOPY Do not copy, already in object. uio_rw The direction of the desired transfer, either UIO_READ, or UIO_WRITE. uio_td The pointer to a struct thread for the associated thread; used if uio_segflg indicates that the transfer is to be made from/to a process's address space. RETURN VALUES
On success uiomove() will return 0, on error it will return an appropriate errno. ERRORS
uiomove() will fail and return the following error code if: [EFAULT] The invoked copyin(9) or copyout(9) returned EFAULT EXAMPLES
The idea is that the driver maintains a private buffer for its data, and processes the request in chunks of maximal the size of this buffer. Note that the buffer handling below is very simplified and will not work (the buffer pointer is not being advanced in case of a partial read), it is just here to demonstrate the uio handling. /* MIN() can be found there: */ #include <sys/param.h> #define BUFSIZE 512 static char buffer[BUFSIZE]; static int data_available; /* amount of data that can be read */ static int fooread(dev_t dev, struct uio *uio, int flag) { int rv, amnt; rv = 0; while (uio->uio_resid > 0) { if (data_available > 0) { amnt = MIN(uio->uio_resid, data_available); rv = uiomove(buffer, amnt, uio); if (rv != 0) break; data_available -= amnt; } else tsleep(...); /* wait for a better time */ } if (rv != 0) { /* do error cleanup here */ } return (rv); } SEE ALSO
read(2), readv(2), write(2), writev(2), copyin(9), copyout(9), sleep(9) HISTORY
The uio mechanism appeared in some early version of UNIX. AUTHORS
This manual page was written by Jorg Wunsch. BSD
March 21, 2010 BSD
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