243 lines
7.2 KiB
Groff
243 lines
7.2 KiB
Groff
.\"
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.\" Copyright (c) 1998, 1999 Kenneth D. Merry.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 3, 2017
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.Dt PASS 4
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.Os
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.Sh NAME
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.Nm pass
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.Nd CAM application passthrough driver
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.Sh SYNOPSIS
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.Cd device pass
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.Sh DESCRIPTION
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The
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.Nm
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driver provides a way for userland applications to issue CAM CCBs to the
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kernel.
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.Pp
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Since the
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.Nm
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driver allows direct access to the CAM subsystem, system administrators
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should exercise caution when granting access to this driver.
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If used
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improperly, this driver can allow userland applications to crash a machine
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or cause data loss.
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.Pp
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The
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.Nm
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driver attaches to every
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.Tn SCSI
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and
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.Tn ATA
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device found in the system.
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Since it attaches to every device, it provides a generic means of accessing
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.Tn SCSI
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and
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.Tn ATA
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devices, and allows the user to access devices which have no
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"standard" peripheral driver associated with them.
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.Sh KERNEL CONFIGURATION
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It is only necessary to configure one
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.Nm
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device in the kernel;
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.Nm
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devices are automatically allocated as
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.Tn SCSI
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and
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.Tn ATA
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devices are found.
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.Sh IOCTLS
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.Bl -tag -width 5n
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.It CAMIOCOMMAND union ccb *
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This ioctl takes most kinds of CAM CCBs and passes them through to the CAM
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transport layer for action.
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Note that some CCB types are not allowed
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through the passthrough device, and must be sent through the
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.Xr xpt 4
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device instead.
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Some examples of xpt-only CCBs are XPT_SCAN_BUS,
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XPT_DEV_MATCH, XPT_RESET_BUS, XPT_SCAN_LUN, XPT_ENG_INQ, and XPT_ENG_EXEC.
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These CCB types have various attributes that make it illogical or
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impossible to service them through the passthrough interface.
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.Pp
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If the user would like the kernel to do error recovery, the
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.Dv CAM_PASS_ERR_RECOVER
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flag must be set on the CCB, and the retry_count field set to the number
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of retries.
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.It CAMGETPASSTHRU union ccb *
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This ioctl takes an XPT_GDEVLIST CCB, and returns the passthrough device
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corresponding to the device in question.
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Although this ioctl is available through the
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.Nm
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driver, it is of limited use, since the caller must already know that
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the device in question is a passthrough device if they are issuing this
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ioctl.
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It is probably more useful to issue this ioctl through the
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.Xr xpt 4
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device.
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.It CAMIOQUEUE union ccb *
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Queue a CCB to the
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.Nm
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driver to be executed asynchronously.
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The caller may use
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.Xr select 2 ,
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.Xr poll 2
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or
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.Xr kevent 2
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to receive notification when the CCB has completed.
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.Pp
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This ioctl takes most CAM CCBs, but some CCB types are not allowed through
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the pass device, and must be sent through the
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.Xr xpt 4
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device instead.
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Some examples of xpt-only CCBs are XPT_SCAN_BUS,
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XPT_DEV_MATCH, XPT_RESET_BUS, XPT_SCAN_LUN, XPT_ENG_INQ, and XPT_ENG_EXEC.
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These CCB types have various attributes that make it illogical or
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impossible to service them through the passthrough interface.
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.Pp
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Although the
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.Dv CAMIOQUEUE
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ioctl is not defined to take an argument, it does require a
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pointer to a union ccb.
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It is not defined to take an argument to avoid an extra malloc and copy
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inside the generic
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.Xr ioctl 2
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handler.
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.Pp
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The completed CCB will be returned via the
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.Dv CAMIOGET
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ioctl.
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An error will only be returned from the
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.Dv CAMIOQUEUE
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ioctl if there is an error allocating memory for the request or copying
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memory from userland.
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All other errors will be reported as standard CAM CCB status errors.
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Since the CCB is not copied back to the user process from the pass driver
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in the
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.Dv CAMIOQUEUE
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ioctl, the user's passed-in CCB will not be modified.
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This is the case even with immediate CCBs.
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Instead, the completed CCB must be retrieved via the
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.Dv CAMIOGET
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ioctl and the status examined.
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.Pp
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Multiple CCBs may be queued via the
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.Dv CAMIOQUEUE
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ioctl at any given time, and they may complete in a different order than
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the order that they were submitted.
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The caller must take steps to identify CCBs that are queued and completed.
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The
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.Dv periph_priv
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structure inside struct ccb_hdr is available for userland use with the
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.Dv CAMIOQUEUE
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and
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.Dv CAMIOGET
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ioctls, and will be preserved across calls.
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Also, the periph_links linked list pointers inside struct ccb_hdr are
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available for userland use with the
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.Dv CAMIOQUEUE
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and
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.Dv CAMIOGET
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ioctls and will be preserved across calls.
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.Pp
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If the user would like the kernel to do error recovery, the
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.Dv CAM_PASS_ERR_RECOVER
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flag must be set on the CCB, and the retry_count field set to the number
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of retries.
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.It CAMIOGET union ccb *
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Retrieve completed CAM CCBs queued via the
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.Dv CAMIOQUEUE
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ioctl.
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An error will only be returned from the
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.Dv CAMIOGET
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ioctl if the
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.Nm
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driver fails to copy data to the user process or if there are no completed
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CCBs available to retrieve.
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If no CCBs are available to retrieve,
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errno will be set to
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.Dv ENOENT .
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.Pp
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All other errors will be reported as standard CAM CCB status errors.
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.Pp
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Although the
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.Dv CAMIOGET
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ioctl is not defined to take an argument, it does require a
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pointer to a union ccb.
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It is not defined to take an argument to avoid an extra malloc and copy
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inside the generic
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.Xr ioctl 2
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handler.
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.Pp
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The pass driver will report via
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.Xr select 2 ,
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.Xr poll 2
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or
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.Xr kevent 2
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when a CCB has completed.
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One CCB may be retrieved per
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.Dv CAMIOGET
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call.
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CCBs may be returned in an order different than the order they were
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submitted.
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So the caller should use the
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.Dv periph_priv
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area inside the CCB header to store pointers to identifying information.
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.El
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.Sh FILES
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.Bl -tag -width /dev/passn -compact
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.It Pa /dev/pass Ns Ar n
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Character device nodes for the
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.Nm
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driver.
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There should be one of these for each device accessed through the
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CAM subsystem.
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.El
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.Sh DIAGNOSTICS
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None.
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.Sh SEE ALSO
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.Xr kqueue 2 ,
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.Xr poll 2 ,
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.Xr select 2 ,
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.Xr cam 3 ,
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.Xr cam_cdbparse 3 ,
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.Xr cam 4 ,
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.Xr cd 4 ,
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.Xr ctl 4 ,
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.Xr da 4 ,
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.Xr sa 4 ,
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.Xr xpt 4 ,
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.Xr camcontrol 8 ,
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.Xr camdd 8
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.Sh HISTORY
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The CAM passthrough driver first appeared in
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.Fx 3.0 .
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.Sh AUTHORS
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.An Kenneth Merry Aq Mt ken@FreeBSD.org
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