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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.
89 If the user would like the kernel to do error recovery, the
90 .Dv CAM_PASS_ERR_RECOVER
91 flag must be set on the CCB, and the retry_count field set to the number
93 .It CAMGETPASSTHRU union ccb *
94 This ioctl takes an XPT_GDEVLIST CCB, and returns the passthrough device
95 corresponding to the device in question.
96 Although this ioctl is available through the
98 driver, it is of limited use, since the caller must already know that
99 the device in question is a passthrough device if they are issuing this
101 It is probably more useful to issue this ioctl through the
104 .It CAMIOQUEUE union ccb *
107 driver to be executed asynchronously.
113 to receive notification when the CCB has completed.
115 This ioctl takes most CAM CCBs, but some CCB types are not allowed through
116 the pass device, and must be sent through the
119 Some examples of xpt-only CCBs are XPT_SCAN_BUS,
120 XPT_DEV_MATCH, XPT_RESET_BUS, XPT_SCAN_LUN, XPT_ENG_INQ, and XPT_ENG_EXEC.
121 These CCB types have various attributes that make it illogical or
122 impossible to service them through the passthrough interface.
126 ioctl is not defined to take an argument, it does require a
127 pointer to a union ccb.
128 It is not defined to take an argument to avoid an extra malloc and copy
133 The completed CCB will be returned via the
136 An error will only be returned from the
138 ioctl if there is an error allocating memory for the request or copying
139 memory from userland.
140 All other errors will be reported as standard CAM CCB status errors.
141 Since the CCB is not copied back to the user process from the pass driver
144 ioctl, the user's passed-in CCB will not be modfied.
145 This is the case even with immediate CCBs.
146 Instead, the completed CCB must be retrieved via the
148 ioctl and the status examined.
150 Multiple CCBs may be queued via the
152 ioctl at any given time, and they may complete in a different order than
153 the order that they were submitted.
154 The caller must take steps to identify CCBs that are queued and completed.
157 structure inside struct ccb_hdr is available for userland use with the
161 ioctls, and will be preserved across calls.
162 Also, the periph_links linked list pointers inside struct ccb_hdr are
163 available for userland use with the
167 ioctls and will be preserved across calls.
169 If the user would like the kernel to do error recovery, the
170 .Dv CAM_PASS_ERR_RECOVER
171 flag must be set on the CCB, and the retry_count field set to the number
173 .It CAMIOGET union ccb *
174 Retrieve completed CAM CCBs queued via the
177 An error will only be returned from the
181 driver fails to copy data to the user process or if there are no completed
182 CCBs available to retrieve.
183 If no CCBs are available to retrieve,
187 All other errors will be reported as standard CAM CCB status errors.
191 ioctl is not defined to take an argument, it does require a
192 pointer to a union ccb.
193 It is not defined to take an argument to avoid an extra malloc and copy
198 The pass driver will report via
203 when a CCB has completed.
204 One CCB may be retrieved per
207 CCBs may be returned in an order different than the order they were
209 So the caller should use the
211 area inside the CCB header to store pointers to identifying information.
214 .Bl -tag -width /dev/passn -compact
215 .It Pa /dev/pass Ns Ar n
216 Character device nodes for the
219 There should be one of these for each device accessed through the
239 The CAM passthrough driver first appeared in
242 .An Kenneth Merry Aq ken@FreeBSD.org