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37 .Nd initiate I/O on raw devices
44 .Fn physio "struct cdev *dev" "struct uio *uio" "int ioflag"
48 is a helper function typically called from character device
52 routines to start I/O on a user process buffer.
53 The maximum amount of data to transfer with each call
55 .Fa dev->si_iosize_max .
58 call converts the I/O request into a
60 request and passes the new request to the driver's
62 routine for processing.
66 normally describes user space addresses,
68 needs to lock those pages into memory.
69 This is done by calling
71 for the appropriate pages.
73 always awaits the completion of the entire requested transfer before
74 returning, unless an error condition is detected earlier.
76 A break-down of the arguments follows:
77 .Bl -tag -width indent
79 The device number identifying the device to interact with.
81 The description of the entire transfer as requested by the user process.
82 Currently, the results of passing a
86 set to anything other than
90 The ioflag argument from the
102 is returned if the address range described by
104 is not accessible by the requesting process.
106 will return any error resulting from calls to the device strategy routine,
112 Note that the actual transfer size may be less than requested by
114 if the device signals an
123 manual page is originally from
125 with minor changes for applicability with
130 call has been completely re-written for providing higher
131 I/O and paging performance.