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34 .\" $NetBSD: physio.9,v 1.2 1996/11/11 00:05:12 lukem Exp $
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73 .Dd November 9, 2008
74 .Dt PHYSIO 9
75 .Os
76 .Sh NAME
77 .Nm physread ,
78 .Nm physwrite
79 .Nd initiate I/O on raw devices
80 .Sh SYNOPSIS
81 .In sys/buf.h
82 .In sys/device.h
83 .Ft int
84 .Fn physread "struct dev_read_args *ap"
85 .Ft int
86 .Fn physwrite "struct dev_write_args *ap"
87 .Sh DESCRIPTION
88 .Fn Physread
89 and
90 .Fn physwrite
91 are helper functions typically called from character device read and write
92 routines to start I/O on a user process buffer.
93 They will call the
94 .Fn dev_dstrategy
95 routine one or more times depending on the size of transfer which is
96 described by the
97 .Fa ap
98 argument.
99 .Pp
100 The maximum amount of data transferable in one iteration of the
101 .Fn physread
102 and
103 .Fn physwrite
104 functions is determined by the maximum I/O size supported by the device
105 .Fa dev ,
106 otherwise the value of
107 .Dv MAXPHYS
108 is used.
109 Until the I/O operation is complete, the calling process or thread is
110 put to sleep with the wait message set to
111 .Ql "physstr" .
112 .Pp
113 The
114 .Fn physread
115 and
116 .Fn physwrite
117 functions always await the completion of the entire requested transfer
118 before returning, unless an error condition is detected earlier.
119 .Pp
120 The
121 .Fa ap
122 argument is a pointer to a
123 .Vt dev_read_args
124 or
125 .Vt dev_write_args
126 structure, as passed to
127 .Nm d_read
128 or
129 .Nm d_write .
130 .Sh RETURN VALUES
131 If successful
132 .Fn physread
133 and
134 .Fn physwrite
135 will return 0.
136 .Pp
137 The
138 .Va errno
139 value
140 .Er EFAULT
141 will be returned if the address range described by
142 .Fa uio
143 is not accessible by the calling process or thread.
144 .Pp
145 Note that the actual transfer size may be less than requested by
146 .Fa ap
147 if the device signals an
148 .Dq end of file
149 condition.
150 .Sh SEE ALSO
151 .Xr read 2 ,
152 .Xr write 2 ,
153 .Xr uio 9