read(9e) - osol9

1read(9E)                      Driver Entry Points                     read(9E)
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NAME

6       read - read data from a device
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SYNOPSIS

9       #include <sys/types.h>
10       #include <sys/errno.h>
11       #include <sys/open.h>
12       #include <sys/uio.h>
13       #include <sys/cred.h>
14       #include <sys/ddi.h>
15       #include <sys/sunddi.h>
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19       int prefixread(dev_t dev, struct uio *uio_p, cred_t *cred_p);
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INTERFACE LEVEL

23       Architecture  independent  level  1  (DDI/DKI).  This  entry  point  is
24       optional.
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PARAMETERS

27       dev        Device number.
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30       uio_p      Pointer to the  uio(9S) structure that describes  where  the
31                  data is to be stored in user space.
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34       cred_p     Pointer to the  user credential structure for the I/O trans‐
35                  action.
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DESCRIPTION

39       The driver  read() routine is called indirectly through  cb_ops(9S)  by
40       the  read(2) system call. The  read() routine should check the validity
41       of the minor number component of dev and the user credential  structure
42       pointed to by  cred_p (if pertinent). The  read() routine should super‐
43       vise the data transfer into the user space described  by  the   uio(9S)
44       structure.
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RETURN VALUES

47       The   read()  routine  should return  0 for success, or the appropriate
48       error number.
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EXAMPLES

51       Example 1 read() routine using physio()
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54       The following is an example of a read()  routine  using  physio(9F)  to
55       perform reads from a non-seekable device:
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58               static int
59               xxread(dev_t dev, struct uio *uiop, cred_t *credp)
60               {
61                        int                 rval;
62                        offset_t            off;
63                        int                 instance;
64                        xx_t                xx;
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66                        instance = getminor(dev);
67                        xx = ddi_get_soft_state(xxstate, instance);
68                        if (xx == NULL)
69                                  return (ENXIO);
70                        off = uiop->uio_loffset;
71                        rval = physio(xxstrategy, NULL, dev, B_READ,
72                                  xxmin, uiop);
73                        uiop->uio_loffset = off;
74                        return (rval);
75               }
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