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35 .Nd kernel disk storage API
41 .Fn disk_create "struct disk *disk" "int version"
43 .Fn disk_gone "struct disk *disk"
45 .Fn disk_destroy "struct disk *disk"
47 .Fn disk_resize "struct disk *disk" "int flags"
49 .Fn disk_add_alias "struct disk *disk" "const char *alias"
51 The disk storage API permits kernel device drivers providing access to
52 disk-like storage devices to advertise the device to other kernel
58 Each disk device is described by a
60 structure, which contains a variety of parameters for the disk device,
61 function pointers for various methods that may be performed on the device,
62 as well as private data storage for the device driver.
63 In addition, some fields are reserved for use by GEOM in managing access
64 to the device and its statistics.
66 GEOM has the ownership of
68 and drivers must allocate storage for it with the
71 fill in the fields and call
73 when the device is ready to service requests.
75 adds an alias for the disk and must be called before
77 but may be called multiple times.
78 For each alias added, a device node will be created with
80 in the same way primary device nodes are created with
86 Care should be taken to ensure that only one driver creates aliases
89 can be called by the driver after modifying
91 to notify GEOM about the disk capacity change.
94 field should be set to either M_WAITOK, or M_NOWAIT.
96 orphans all of the providers associated with the drive, setting an error
97 condition of ENXIO in each one.
98 In addition, it prevents a re-taste on last close for writing if an error
99 condition has been set in the provider.
102 the device driver is not allowed to access the contents of
109 takes a second parameter,
111 which must always be passed
113 If GEOM detects that the driver is compiled against an unsupported version,
114 it will ignore the device and print a warning on the console.
115 .Ss Descriptive Fields
116 The following fields identify the disk device described by the structure
117 instance, and must be filled in prior to submitting the structure to
119 and may not be subsequently changed:
120 .Bl -tag -width indent
121 .It Vt u_int Va d_flags
122 Optional flags indicating to the storage framework what optional features
123 or descriptions the storage device driver supports.
124 Currently supported flags are
126 (maintained by storage framework),
127 .Dv DISKFLAG_CANDELETE
128 (maintained by device driver),
130 .Dv DISKFLAG_CANFLUSHCACHE
131 (maintained by device driver).
132 .It Vt "const char *" Va d_name
133 Holds the name of the storage device class, e.g.,
135 This value typically uniquely identifies a particular driver device,
136 and must not conflict with devices serviced by other device drivers.
137 .It Vt u_int Va d_unit
138 Holds the instance of the storage device class, e.g.,
140 This namespace is managed by the device driver, and assignment of unit
141 numbers might be a property of probe order, or in some cases topology.
146 values will uniquely identify a disk storage device.
148 .Ss Disk Device Methods
149 The following fields identify various disk device methods, if implemented:
150 .Bl -tag -width indent
151 .It Vt "disk_open_t *" Va d_open
152 Optional: invoked when the disk device is opened.
153 If no method is provided, open will always succeed.
154 .It Vt "disk_close_t *" Va d_close
155 Optional: invoked when the disk device is closed.
156 Although an error code may be returned, the call should always terminate
157 any state setup by the corresponding open method call.
158 .It Vt "disk_strategy_t *" Va d_strategy
159 Mandatory: invoked when a new
161 is to be initiated on the disk device.
162 .It Vt "disk_ioctl_t *" Va d_ioctl
163 Optional: invoked when an I/O control operation is initiated on the disk device.
164 Please note that for security reasons these operations should not
165 be able to affect other devices than the one on which they are performed.
166 .It Vt "dumper_t *" Va d_dump
167 Optional: if configured with
169 this function is invoked from a very restricted system state after a
170 kernel panic to record a copy of the system RAM to the disk.
171 .It Vt "disk_getattr_t *" Va d_getattr
172 Optional: if this method is provided, it gives the disk driver the
173 opportunity to override the default GEOM response to BIO_GETATTR requests.
174 This function should return -1 if the attribute is not handled, 0 if the
175 attribute is handled, or an errno to be passed to g_io_deliver().
176 .It Vt "disk_gone_t *" Va d_gone
177 Optional: if this method is provided, it will be called after disk_gone()
178 is called, once GEOM has finished its cleanup process.
179 Once this callback is called, it is safe for the disk driver to free all of
180 its resources, as it will not be receiving further calls from GEOM.
182 .Ss Mandatory Media Properties
183 The following fields identify the size and granularity of the disk device.
184 These fields must stay stable from return of the drivers open method until
185 the close method is called, but it is perfectly legal to modify them in
186 the open method before returning.
187 .Bl -tag -width indent
188 .It Vt u_int Va d_sectorsize
189 The sector size of the disk device in bytes.
190 .It Vt off_t Va d_mediasize
191 The size of the disk device in bytes.
192 .It Vt u_int Va d_maxsize
193 The maximum supported size in bytes of an I/O request.
194 Requests larger than this size will be chopped up by GEOM.
196 .Ss Optional Media Properties
197 These optional fields can provide extra information about the disk
199 Do not initialize these fields if the field/concept does not apply.
200 These fields must stay stable from return of the drivers open method until
201 the close method is called, but it is perfectly legal to modify them in
202 the open method before returning.
203 .Bl -tag -width indent
204 .It Vt u_int Va d_fwsectors , Vt u_int Va d_fwheads
205 The number of sectors and heads advertised on the disk device by the
207 These values are almost universally bogus, but on some architectures
208 necessary for the correct calculation of disk partitioning.
209 .It Vt u_int Va d_stripeoffset , Vt u_int Va d_stripesize
210 These two fields can be used to describe the width and location of
211 natural performance boundaries for most disk technologies.
213 .Pa src/sys/geom/notes
215 .It Vt char Va d_ident[DISK_IDENT_SIZE]
216 This field can and should be used to store disk's serial number if the
217 d_getattr method described above isn't implemented, or if it does not
218 support the GEOM::ident attribute.
219 .It Vt char Va d_descr[DISK_IDENT_SIZE]
220 This field can be used to store the disk vendor and product description.
221 .It Vt uint16_t Va d_hba_vendor
222 This field can be used to store the PCI vendor ID for the HBA connected to
224 .It Vt uint16_t Va d_hba_device
225 This field can be used to store the PCI device ID for the HBA connected to
227 .It Vt uint16_t Va d_hba_subvendor
228 This field can be used to store the PCI subvendor ID for the HBA connected to
230 .It Vt uint16_t Va d_hba_subdevice
231 This field can be used to store the PCI subdevice ID for the HBA connected to
234 .Ss Driver Private Data
235 This field may be used by the device driver to store a pointer to
236 private data to implement the disk service.
237 .Bl -tag -width indent
238 .It Vt "void *" Va d_drv1
239 Private data pointer.
240 Typically used to store a pointer to the drivers
242 structure for this disk device.
249 This manual page was written by
252 Disk aliases are not a general purpose aliasing mechanism, but are
253 intended only to ease the transition from one name to another.
254 They can be used to ensure that nvd0 and nda0 are the same thing.
255 They cannot be used to implement the diskX concept from macOS.