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44 .Nd initiate I/O on raw devices
51 .Fn physio "dev_t dev" "struct uio *uio" "int ioflag"
55 is a helper function typically called from character device
59 routines to start I/O on a user process buffer.
60 The maximum amount of data to transfer with each call
62 .Fa dev->si_iosize_max .
65 call converts the I/O request into a
67 request and passes the new request to the driver's
69 routine for processing.
73 normally describes user space addresses,
75 needs to lock those pages into memory.
76 This is done by calling
78 for the appropriate pages.
80 always awaits the completion of the entire requested transfer before
81 returning, unless an error condition is detected earlier.
83 A break-down of the arguments follows:
84 .Bl -tag -width indent
86 The device number identifying the device to interact with.
88 The description of the entire transfer as requested by the user process.
89 Currently, the results of passing a
93 set to anything other than
97 The ioflag argument from the
109 is returned if the address range described by
111 is not accessible by the requesting process.
113 will return any error resulting from calls to the device strategy routine,
119 Note that the actual transfer size may be less than requested by
121 if the device signals an
130 manual page is originally from
132 with minor changes for applicability with
137 call has been completely re-written for providing higher
138 I/O and paging performance.