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/share/man/man9/disk.9

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 28.\" $FreeBSD$
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 30.Dd February 18, 2004
 31.Dt DISK 9
 32.Os
 33.Sh NAME
 34.Nm disk
 35.Nd kernel disk storage API
 36.Sh SYNOPSIS
 37.In geom/geom_disk.h
 38.Ft struct disk *
 39.Fn disk_alloc void
 40.Ft void
 41.Fn disk_create "struct disk *disk" "int version"
 42.Ft void
 43.Fn disk_gone "struct disk *disk"
 44.Ft void
 45.Fn disk_destroy "struct disk *disk"
 46.Sh DESCRIPTION
 47The disk storage API permits kernel device drivers providing access to
 48disk-like storage devices to advertise the device to other kernel
 49components, including
 50.Xr GEOM 4
 51and
 52.Xr devfs 5 .
 53.Pp
 54Each disk device is described by a
 55.Vt "struct disk"
 56structure, which contains a variety of parameters for the disk device,
 57function pointers for various methods that may be performed on the device,
 58as well as private data storage for the device driver.
 59In addition, some fields are reserved for use by GEOM in managing access
 60to the device and its statistics.
 61.Pp
 62GEOM has the ownership of
 63.Vt "struct disk" ,
 64and drivers must allocate storage for it with the
 65.Fn disk_alloc
 66function,
 67fill in the fields and call
 68.Fn disk_create
 69when the device is ready to service requests.
 70.Fn disk_gone
 71orphans all of the providers associated with the drive, setting an error
 72condition of ENXIO in each one.
 73In addition, it prevents a re-taste on last close for writing if an error
 74condition has been set in the provider.
 75After calling
 76.Fn disk_destroy ,
 77the device driver is not allowed to access the contents of
 78.Vt "struct disk"
 79anymore.
 80.Pp
 81The
 82.Fn disk_create
 83function
 84takes a second parameter,
 85.Fa version ,
 86which must always be passed
 87.Dv DISK_VERSION .
 88If GEOM detects that the driver is compiled against an unsupported version,
 89it will ignore the device and print a warning on the console.
 90.Ss Descriptive Fields
 91The following fields identify the disk device described by the structure
 92instance, and must be filled in prior to submitting the structure to
 93.Fn disk_create
 94and may not be subsequently changed:
 95.Bl -tag -width indent
 96.It Vt u_int Va d_flags
 97Optional flags indicating to the storage framework what optional features
 98or descriptions the storage device driver supports.
 99Currently supported flags are
100.Dv DISKFLAG_NEEDSGIANT
101(maintained by device driver),
102.Dv DISKFLAG_OPEN
103(maintained by storage framework),
104.Dv DISKFLAG_CANDELETE
105(maintained by device driver),
106and
107.Dv DISKFLAG_CANFLUSHCACHE
108(maintained by device driver).
109.It Vt "const char *" Va d_name
110Holds the name of the storage device class, e.g.,
111.Dq Li ahd .
112This value typically uniquely identifies a particular driver device,
113and must not conflict with devices serviced by other device drivers.
114.It Vt u_int Va d_unit
115Holds the instance of the storage device class, e.g.,
116.Dq Li 4 .
117This namespace is managed by the device driver, and assignment of unit
118numbers might be a property of probe order, or in some cases topology.
119Together, the
120.Va d_name
121and
122.Va d_unit
123values will uniquely identify a disk storage device.
124.El
125.Ss Disk Device Methods
126The following fields identify various disk device methods, if implemented:
127.Bl -tag -width indent
128.It Vt "disk_open_t *" Va d_open
129Optional: invoked when the disk device is opened.
130If no method is provided, open will always succeed.
131.It Vt "disk_close_t *" Va d_close
132Optional: invoked when the disk device is closed.
133Although an error code may be returned, the call should always terminate
134any state setup by the corresponding open method call.
135.It Vt "disk_strategy_t *" Va d_strategy
136Mandatory: invoked when a new
137.Vt "struct bio"
138is to be initiated on the disk device.
139.It Vt "disk_ioctl_t *" Va d_ioctl
140Optional: invoked when an I/O control operation is initiated on the disk device.
141Please note that for security reasons these operations should not
142be able to affect other devices than the one on which they are performed.
143.It Vt "dumper_t *" Va d_dump
144Optional: if configured with
145.Xr dumpon 8 ,
146this function is invoked from a very restricted system state after a
147kernel panic to record a copy of the system RAM to the disk.
148.It Vt "disk_getattr_t *" Va d_getattr
149Optional: if this method is provided, it gives the disk driver the
150opportunity to override the default GEOM response to BIO_GETATTR requests.
151This function should return -1 if the attribute is not handled, 0 if the
152attribute is handled, or an errno to be passed to g_io_deliver().
153.It Vt "disk_gone_t *" Va d_gone
154Optional: if this method is provided, it will be called after disk_gone()
155is called, once GEOM has finished its cleanup process.
156Once this callback is called, it is safe for the disk driver to free all of
157its resources, as it will not be receiving further calls from GEOM.
158.El
159.Ss Mandatory Media Properties
160The following fields identify the size and granularity of the disk device.
161These fields must stay stable from return of the drivers open method until
162the close method is called, but it is perfectly legal to modify them in
163the open method before returning.
164.Bl -tag -width indent
165.It Vt u_int Va d_sectorsize
166The sector size of the disk device in bytes.
167.It Vt off_t Va d_mediasize
168The size of the disk device in bytes.
169.It Vt u_int Va d_maxsize
170The maximum supported size in bytes of an I/O request.
171Requests larger than this size will be chopped up by GEOM.
172.El
173.Ss Optional Media Properties
174These optional fields can provide extra information about the disk
175device.
176Do not initialize these fields if the field/concept does not apply.
177These fields must stay stable from return of the drivers open method until
178the close method is called, but it is perfectly legal to modify them in
179the open method before returning.
180.Bl -tag -width indent
181.It Vt u_int Va d_fwsectors , Vt u_int Va d_fwheads
182The number of sectors and heads advertised on the disk device by the
183firmware or BIOS.
184These values are almost universally bogus, but on some architectures
185necessary for the correct calculation of disk partitioning.
186.It Vt u_int Va d_stripeoffset , Vt u_int Va d_stripesize
187These two fields can be used to describe the width and location of
188natural performance boundaries for most disk technologies.
189Please see
190.Pa src/sys/geom/notes
191for details.
192.It Vt char Va d_ident[DISK_IDENT_SIZE]
193This field can and should be used to store disk's serial number if the
194d_getattr method described above isn't implemented, or if it does not
195support the GEOM::ident attribute.
196.It Vt char Va d_descr[DISK_IDENT_SIZE]
197This field can be used to store the disk vendor and product description.
198.It Vt uint16_t Va d_hba_vendor
199This field can be used to store the PCI vendor ID for the HBA connected to
200the disk.
201.It Vt uint16_t Va d_hba_device
202This field can be used to store the PCI device ID for the HBA connected to
203the disk.
204.It Vt uint16_t Va d_hba_subvendor
205This field can be used to store the PCI subvendor ID for the HBA connected to
206the disk.
207.It Vt uint16_t Va d_hba_subdevice
208This field can be used to store the PCI subdevice ID for the HBA connected to
209the disk.
210.El
211.Ss Driver Private Data
212This field may be used by the device driver to store a pointer to
213private data to implement the disk service.
214.Bl -tag -width indent
215.It Vt "void *" Va d_drv1
216Private data pointer.
217Typically used to store a pointer to the drivers
218.Vt softc
219structure for this disk device.
220.El
221.Sh SEE ALSO
222.Xr GEOM 4 ,
223.Xr devfs 5
224.Sh AUTHORS
225This manual page was written by
226.An Robert Watson .