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freebsd-nq/share/man/man9/disk.9
Kenneth D. Merry c3fb2891f0 Fix a bug which causes a panic in daopen(). The panic is caused by 
a da(4) instance going away while GEOM is still probing it.

In this case, the GEOM disk class instance has been created by
disk_create(), and the taste of the disk is queued in the GEOM
event queue.

While that event is queued, the da(4) instance goes away.  When the
open call comes into the da(4) driver, it dereferences the freed
(but non-NULL) peripheral pointer provided by GEOM, which results
in a panic.

The solution is to add a callback to the GEOM disk code that is
called when all of its resources are cleaned up.  This is
implemented inside GEOM by adding an optional callback that is
called when all consumers have detached from a provider, and the
provider is about to be deleted.

scsi_cd.c,
scsi_da.c:	In the register routine for the cd(4) and da(4)
		routines, acquire a reference to the CAM peripheral
		instance just before we call disk_create().

		Use the new GEOM disk d_gone() callback to register
		a callback (dadiskgonecb()/cddiskgonecb()) that
		decrements the peripheral reference count once GEOM
		has finished cleaning up its resources.

		In the cd(4) driver, clean up open and close
		behavior slightly.  GEOM makes sure we only get one
		open() and one close call, so there is no need to
		set an open flag and decrement the reference count
		if we are not the first open.

		In the cd(4) driver, use cam_periph_release_locked()
		in a couple of error scenarios to avoid extra mutex
		calls.

geom.h:		Add a new, optional, providergone callback that
		is called when a provider is about to be deleted.

geom_disk.h:	Add a new d_gone() callback to the GEOM disk
		interface.

		Bump the DISK_VERSION to version 2.  This probably
		should have been done after a couple of previous
		changes, especially the addition of the d_getattr()
		callback.

geom_disk.c:	Add a providergone callback for the disk class,
		g_disk_providergone(), that calls the user's
		d_gone() callback if it exists.

		Bump the DISK_VERSION to 2.

geom_subr.c:	In g_destroy_provider(), call the providergone
		callback if it has been provided.

		In g_new_geomf(), propagate the class's
		providergone callback to the new geom instance.

blkfront.c:	Callers of disk_create() are supposed to pass in
		DISK_VERSION, not an explicit disk API version
		number.  Update the blkfront driver to do that.

disk.9:		Update the disk(9) man page to include information
		on the new d_gone() callback, as well as the
		previously added d_getattr() callback, d_descr
		field, and HBA PCI ID fields.

MFC after:	5 days
2012-06-24 04:29:03 +00:00

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.\"
.\" Copyright (c) 2003 Robert N. M. Watson
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.\" $FreeBSD$
.\"
.Dd February 18, 2004
.Dt DISK 9
.Os
.Sh NAME
.Nm disk
.Nd kernel disk storage API
.Sh SYNOPSIS
.In geom/geom_disk.h
.Ft struct disk *
.Fn disk_alloc void
.Ft void
.Fn disk_create "struct disk *disk" "int version"
.Ft void
.Fn disk_gone "struct disk *disk"
.Ft void
.Fn disk_destroy "struct disk *disk"
.Sh DESCRIPTION
The disk storage API permits kernel device drivers providing access to
disk-like storage devices to advertise the device to other kernel
components, including
.Xr GEOM 4
and
.Xr devfs 5 .
.Pp
Each disk device is described by a
.Vt "struct disk"
structure, which contains a variety of parameters for the disk device,
function pointers for various methods that may be performed on the device,
as well as private data storage for the device driver.
In addition, some fields are reserved for use by GEOM in managing access
to the device and its statistics.
.Pp
GEOM has the ownership of
.Vt "struct disk" ,
and drivers must allocate storage for it with the
.Fn disk_alloc
function,
fill in the fields and call
.Fn disk_create
when the device is ready to service requests.
.Fn disk_gone
orphans all of the providers associated with the drive, setting an error
condition of ENXIO in each one.
In addition, it prevents a re-taste on last close for writing if an error
condition has been set in the provider.
After calling
.Fn disk_destroy ,
the device driver is not allowed to access the contents of
.Vt "struct disk"
anymore.
.Pp
The
.Fn disk_create
function
takes a second parameter,
.Fa version ,
which must always be passed
.Dv DISK_VERSION .
If GEOM detects that the driver is compiled against an unsupported version,
it will ignore the device and print a warning on the console.
.Ss Descriptive Fields
The following fields identify the disk device described by the structure
instance, and must be filled in prior to submitting the structure to
.Fn disk_create
and may not be subsequently changed:
.Bl -tag -width indent
.It Vt u_int Va d_flags
Optional flags indicating to the storage framework what optional features
or descriptions the storage device driver supports.
Currently supported flags are
.Dv DISKFLAG_NEEDSGIANT
(maintained by device driver),
.Dv DISKFLAG_OPEN
(maintained by storage framework),
.Dv DISKFLAG_CANDELETE
(maintained by device driver),
and
.Dv DISKFLAG_CANFLUSHCACHE
(maintained by device driver).
.It Vt "const char *" Va d_name
Holds the name of the storage device class, e.g.,
.Dq Li ahd .
This value typically uniquely identifies a particular driver device,
and must not conflict with devices serviced by other device drivers.
.It Vt u_int Va d_unit
Holds the instance of the storage device class, e.g.,
.Dq Li 4 .
This namespace is managed by the device driver, and assignment of unit
numbers might be a property of probe order, or in some cases topology.
Together, the
.Va d_name
and
.Va d_unit
values will uniquely identify a disk storage device.
.El
.Ss Disk Device Methods
The following fields identify various disk device methods, if implemented:
.Bl -tag -width indent
.It Vt "disk_open_t *" Va d_open
Optional: invoked when the disk device is opened.
If no method is provided, open will always succeed.
.It Vt "disk_close_t *" Va d_close
Optional: invoked when the disk device is closed.
Although an error code may be returned, the call should always terminate
any state setup by the corresponding open method call.
.It Vt "disk_strategy_t *" Va d_strategy
Mandatory: invoked when a new
.Vt "struct bio"
is to be initiated on the disk device.
.It Vt "disk_ioctl_t *" Va d_ioctl
Optional: invoked when an I/O control operation is initiated on the disk device.
Please note that for security reasons these operations should not
be able to affect other devices than the one on which they are performed.
.It Vt "dumper_t *" Va d_dump
Optional: if configured with
.Xr dumpon 8 ,
this function is invoked from a very restricted system state after a
kernel panic to record a copy of the system RAM to the disk.
.It Vt "disk_getattr_t *" Va d_getattr
Optional: if this method is provided, it gives the disk driver the
opportunity to override the default GEOM response to BIO_GETATTR requests.
This function should return -1 if the attribute is not handled, 0 if the
attribute is handled, or an errno to be passed to g_io_deliver().
.It Vt "disk_gone_t *" Va d_gone
Optional: if this method is provided, it will be called after disk_gone()
is called, once GEOM has finished its cleanup process.
Once this callback is called, it is safe for the disk driver to free all of
its resources, as it will not be receiving further calls from GEOM.
.El
.Ss Mandatory Media Properties
The following fields identify the size and granularity of the disk device.
These fields must stay stable from return of the drivers open method until
the close method is called, but it is perfectly legal to modify them in
the open method before returning.
.Bl -tag -width indent
.It Vt u_int Va d_sectorsize
The sector size of the disk device in bytes.
.It Vt off_t Va d_mediasize
The size of the disk device in bytes.
.It Vt u_int Va d_maxsize
The maximum supported size in bytes of an I/O request.
Requests larger than this size will be chopped up by GEOM.
.El
.Ss Optional Media Properties
These optional fields can provide extra information about the disk
device.
Do not initialize these fields if the field/concept does not apply.
These fields must stay stable from return of the drivers open method until
the close method is called, but it is perfectly legal to modify them in
the open method before returning.
.Bl -tag -width indent
.It Vt u_int Va d_fwsectors , Vt u_int Va d_fwheads
The number of sectors and heads advertised on the disk device by the
firmware or BIOS.
These values are almost universally bogus, but on some architectures
necessary for the correct calculation of disk partitioning.
.It Vt u_int Va d_stripeoffset , Vt u_int Va d_stripesize
These two fields can be used to describe the width and location of
natural performance boundaries for most disk technologies.
Please see
.Pa src/sys/geom/notes
for details.
.It Vt char Va d_ident[DISK_IDENT_SIZE]
This field can and should be used to store disk's serial number if the
d_getattr method described above isn't implemented, or if it does not
support the GEOM::ident attribute.
.It Vt char Va d_descr[DISK_IDENT_SIZE]
This field can be used to store the disk vendor and product description.
.It Vt uint16_t Va d_hba_vendor
This field can be used to store the PCI vendor ID for the HBA connected to
the disk.
.It Vt uint16_t Va d_hba_device
This field can be used to store the PCI device ID for the HBA connected to
the disk.
.It Vt uint16_t Va d_hba_subvendor
This field can be used to store the PCI subvendor ID for the HBA connected to
the disk.
.It Vt uint16_t Va d_hba_subdevice
This field can be used to store the PCI subdevice ID for the HBA connected to
the disk.
.El
.Ss Driver Private Data
This field may be used by the device driver to store a pointer to
private data to implement the disk service.
.Bl -tag -width indent
.It Vt "void *" Va d_drv1
Private data pointer.
Typically used to store a pointer to the drivers
.Vt softc
structure for this disk device.
.El
.Sh SEE ALSO
.Xr GEOM 4 ,
.Xr devfs 5
.Sh AUTHORS
This manual page was written by
.An Robert Watson .
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