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33 .Nd CAM application passthrough driver
39 driver provides a way for userland applications to issue CAM CCBs to the
44 driver allows direct access to the CAM subsystem, system administrators
45 should exercise caution when granting access to this driver.
47 improperly, this driver can allow userland applications to crash a machine
52 driver attaches to every
56 device found in the system.
57 Since it attaches to every device, it provides a generic means of accessing
61 devices, and allows the user to access devices which have no
62 "standard" peripheral driver associated with them.
63 .Sh KERNEL CONFIGURATION
64 It is only necessary to configure one
68 devices are automatically allocated as
75 .It CAMIOCOMMAND union ccb *
76 This ioctl takes most kinds of CAM CCBs and passes them through to the CAM
77 transport layer for action.
78 Note that some CCB types are not allowed
79 through the passthrough device, and must be sent through the
82 Some examples of xpt-only CCBs are XPT_SCAN_BUS,
83 XPT_DEV_MATCH, XPT_RESET_BUS, XPT_SCAN_LUN, XPT_ENG_INQ, and XPT_ENG_EXEC.
84 These CCB types have various attributes that make it illogical or
85 impossible to service them through the passthrough interface.
87 If the user would like the kernel to do error recovery, the
88 .Dv CAM_PASS_ERR_RECOVER
89 flag must be set on the CCB, and the retry_count field set to the number
91 .It CAMGETPASSTHRU union ccb *
92 This ioctl takes an XPT_GDEVLIST CCB, and returns the passthrough device
93 corresponding to the device in question.
94 Although this ioctl is available through the
96 driver, it is of limited use, since the caller must already know that
97 the device in question is a passthrough device if they are issuing this
99 It is probably more useful to issue this ioctl through the
102 .It CAMIOQUEUE union ccb *
105 driver to be executed asynchronously.
111 to receive notification when the CCB has completed.
113 This ioctl takes most CAM CCBs, but some CCB types are not allowed through
114 the pass device, and must be sent through the
117 Some examples of xpt-only CCBs are XPT_SCAN_BUS,
118 XPT_DEV_MATCH, XPT_RESET_BUS, XPT_SCAN_LUN, XPT_ENG_INQ, and XPT_ENG_EXEC.
119 These CCB types have various attributes that make it illogical or
120 impossible to service them through the passthrough interface.
124 ioctl is not defined to take an argument, it does require a
125 pointer to a union ccb.
126 It is not defined to take an argument to avoid an extra malloc and copy
131 The completed CCB will be returned via the
134 An error will only be returned from the
136 ioctl if there is an error allocating memory for the request or copying
137 memory from userland.
138 All other errors will be reported as standard CAM CCB status errors.
139 Since the CCB is not copied back to the user process from the pass driver
142 ioctl, the user's passed-in CCB will not be modified.
143 This is the case even with immediate CCBs.
144 Instead, the completed CCB must be retrieved via the
146 ioctl and the status examined.
148 Multiple CCBs may be queued via the
150 ioctl at any given time, and they may complete in a different order than
151 the order that they were submitted.
152 The caller must take steps to identify CCBs that are queued and completed.
155 structure inside struct ccb_hdr is available for userland use with the
159 ioctls, and will be preserved across calls.
160 Also, the periph_links linked list pointers inside struct ccb_hdr are
161 available for userland use with the
165 ioctls and will be preserved across calls.
167 If the user would like the kernel to do error recovery, the
168 .Dv CAM_PASS_ERR_RECOVER
169 flag must be set on the CCB, and the retry_count field set to the number
171 .It CAMIOGET union ccb *
172 Retrieve completed CAM CCBs queued via the
175 An error will only be returned from the
179 driver fails to copy data to the user process or if there are no completed
180 CCBs available to retrieve.
181 If no CCBs are available to retrieve,
185 All other errors will be reported as standard CAM CCB status errors.
189 ioctl is not defined to take an argument, it does require a
190 pointer to a union ccb.
191 It is not defined to take an argument to avoid an extra malloc and copy
196 The pass driver will report via
201 when a CCB has completed.
202 One CCB may be retrieved per
205 CCBs may be returned in an order different than the order they were
207 So the caller should use the
209 area inside the CCB header to store pointers to identifying information.
212 .Bl -tag -width /dev/passn -compact
213 .It Pa /dev/pass Ns Ar n
214 Character device nodes for the
217 There should be one of these for each device accessed through the
237 The CAM passthrough driver first appeared in
240 .An Kenneth Merry Aq Mt ken@FreeBSD.org