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uio.9freebsd
Langue: en
Version: 307141 (debian - 07/07/09)
Section: 9 (Appels noyau Linux)
BSD mandoc
NAME
uio uiomove - device driver I/O routinesSYNOPSIS
In sys/types.h In sys/uio.hstruct uio { struct iovec *uio_iov; /* scatter/gather list */ int uio_iovcnt; /* length of scatter/gather list */ off_t uio_offset; /* offset in target object */ int 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
DESCRIPTION
The function Fn 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 Vt struct uio being passed. The transfer request is encoded in this structure. The driver itself should use Fn uiomove 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.
RETURN VALUES
On success Fn uiomove will return 0, on error it will return an appropriate errno.ERRORS
Fn uiomove will fail and return the following error code if:- Bq Er EFAULT
- The invoked copyin(9) or copyout(9) returned Er 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 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 mechanism appeared in some early version of UNIXAUTHORS
This manual page was written by An Jörg Wunsch .Contenus ©2006-2024 Benjamin Poulain
Design ©2006-2024 Maxime Vantorre