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35 .Nd CAM application passthrough driver
41 driver provides a way for userland applications to issue CAM CCBs to the
46 driver allows direct access to the CAM subsystem, system administrators
47 should exercise caution when granting access to this driver.
49 improperly, this driver can allow userland applications to crash a machine
54 driver attaches to every
58 device found in the system.
59 Since it attaches to every device, it provides a generic means of accessing
63 devices, and allows the user to access devices which have no
64 "standard" peripheral driver associated with them.
65 .Sh KERNEL CONFIGURATION
66 It is only necessary to configure one
70 devices are automatically allocated as
77 .It CAMIOCOMMAND union ccb *
78 This ioctl takes most kinds of CAM CCBs and passes them through to the CAM
79 transport layer for action.
80 Note that some CCB types are not allowed
81 through the passthrough device, and must be sent through the
84 Some examples of xpt-only CCBs are XPT_SCAN_BUS,
85 XPT_DEV_MATCH, XPT_RESET_BUS, XPT_SCAN_LUN, XPT_ENG_INQ, and XPT_ENG_EXEC.
86 These CCB types have various attributes that make it illogical or
87 impossible to service them through the passthrough interface.
88 .It CAMGETPASSTHRU union ccb *
89 This ioctl takes an XPT_GDEVLIST CCB, and returns the passthrough device
90 corresponding to the device in question.
91 Although this ioctl is available through the
93 driver, it is of limited use, since the caller must already know that
94 the device in question is a passthrough device if they are issuing this
96 It is probably more useful to issue this ioctl through the
99 .It CAMIOQUEUE union ccb *
102 driver to be executed asynchronously.
108 to receive notification when the CCB has completed.
110 This ioctl takes most CAM CCBs, but some CCB types are not allowed through
111 the pass device, and must be sent through the
114 Some examples of xpt-only CCBs are XPT_SCAN_BUS,
115 XPT_DEV_MATCH, XPT_RESET_BUS, XPT_SCAN_LUN, XPT_ENG_INQ, and XPT_ENG_EXEC.
116 These CCB types have various attributes that make it illogical or
117 impossible to service them through the passthrough interface.
121 ioctl is not defined to take an argument, it does require a
122 pointer to a union ccb.
123 It is not defined to take an argument to avoid an extra malloc and copy
128 The completed CCB will be returned via the
131 An error will only be returned from the
133 ioctl if there is an error allocating memory for the request or copying
134 memory from userland.
135 All other errors will be reported as standard CAM CCB status errors.
136 Since the CCB is not copied back to the user process from the pass driver
139 ioctl, the user's passed-in CCB will not be modfied.
140 This is the case even with immediate CCBs.
141 Instead, the completed CCB must be retrieved via the
143 ioctl and the status examined.
145 Multiple CCBs may be queued via the
147 ioctl at any given time, and they may complete in a different order than
148 the order that they were submitted.
149 The caller must take steps to identify CCBs that are queued and completed.
152 structure inside struct ccb_hdr is available for userland use with the
156 ioctls, and will be preserved across calls.
157 Also, the periph_links linked list pointers inside struct ccb_hdr are
158 available for userland use with the
162 ioctls and will be preserved across calls.
163 .It CAMIOGET union ccb *
164 Retrieve completed CAM CCBs queued via the
167 An error will only be returned from the
171 driver fails to copy data to the user process or if there are no completed
172 CCBs available to retrieve.
173 If no CCBs are available to retrieve,
177 All other errors will be reported as standard CAM CCB status errors.
181 ioctl is not defined to take an argument, it does require a
182 pointer to a union ccb.
183 It is not defined to take an argument to avoid an extra malloc and copy
188 The pass driver will report via
193 when a CCB has completed.
194 One CCB may be retrieved per
197 CCBs may be returned in an order different than the order they were
199 So the caller should use the
201 area inside the CCB header to store pointers to identifying information.
204 .Bl -tag -width /dev/passn -compact
205 .It Pa /dev/pass Ns Ar n
206 Character device nodes for the
209 There should be one of these for each device accessed through the
229 The CAM passthrough driver first appeared in
232 .An Kenneth Merry Aq Mt ken@FreeBSD.org