uio (9)
Leading comments
Copyright (c) 1997 Joerg Wunsch All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or othe...
NAME
uio uiomove uiomove_nofault - device driver I/O routinesSYNOPSIS
In sys/types.h In 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 */
};
Ft int
Fn uiomove void *buf int howmuch struct uio *uiop
Ft int
Fn uiomove_nofault void *buf int howmuch struct uio *uiop
DESCRIPTION
The functions Fn uiomove and Fn uiomove_nofault are used to transfer data between buffers and I/O vectors that might possibly 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 Vt struct uio being passed. The transfer request is encoded in this structure. The driver itself should use Fn uiomove or Fn uiomove_nofault to get at the data in this structure.
The fields in the Vt 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 Vt 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.
The function Fn uiomove_nofault requires that the buffer and I/O vectors be accessible without incurring a page fault. The source and destination addresses must be physically mapped for read and write access, respectively, and neither the source nor destination addresses may be pageable. Thus, the function Fn uiomove_nofault can be called from contexts where acquiring virtual memory system locks or sleeping are prohibited.
RETURN VALUES
On success Fn uiomove and Fn uiomove_nofault will return 0; on error they will return an appropriate error code.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 ifconfig 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(struct cdev *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);
}
ERRORS
Fn uiomove and Fn uiomove_nofault will fail and return the following error code if:- Bq Er EFAULT
- The invoked copyin(9) or copyout(9) returned Er EFAULT
In addition, Fn uiomove_nofault will fail and return the following error code if:
- Bq Er EFAULT
- A page fault occurs.