xref: /freebsd/share/man/man9/disk.9 (revision 6472ac3d8a86336899b6cfb789a4cd9897e3fab5)
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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.El
149.Ss Mandatory Media Properties
150The following fields identify the size and granularity of the disk device.
151These fields must stay stable from return of the drivers open method until
152the close method is called, but it is perfectly legal to modify them in
153the open method before returning.
154.Bl -tag -width indent
155.It Vt u_int Va d_sectorsize
156The sector size of the disk device in bytes.
157.It Vt off_t Va d_mediasize
158The size of the disk device in bytes.
159.It Vt u_int Va d_maxsize
160The maximum supported size in bytes of an I/O request.
161Requests larger than this size will be chopped up by GEOM.
162.El
163.Ss Optional Media Properties
164These optional fields can provide extra information about the disk
165device.
166Do not initialize these fields if the field/concept does not apply.
167These fields must stay stable from return of the drivers open method until
168the close method is called, but it is perfectly legal to modify them in
169the open method before returning.
170.Bl -tag -width indent
171.It Vt u_int Va d_fwsectors , Vt u_int Va d_fwheads
172The number of sectors and heads advertised on the disk device by the
173firmware or BIOS.
174These values are almost universally bogus, but on some architectures
175necessary for the correct calculation of disk partitioning.
176.It Vt u_int Va d_stripeoffset , Vt u_int Va d_stripesize
177These two fields can be used to describe the width and location of
178natural performance boundaries for most disk technologies.
179Please see
180.Pa src/sys/geom/notes
181for details.
182.It Vt char Va d_ident[DISK_IDENT_SIZE]
183This field can and should be used to store disk's serial number.
184.El
185.Ss Driver Private Data
186This field may be used by the device driver to store a pointer to
187private data to implement the disk service.
188.Bl -tag -width indent
189.It Vt "void *" Va d_drv1
190Private data pointer.
191Typically used to store a pointer to the drivers
192.Vt softc
193structure for this disk device.
194.El
195.Sh SEE ALSO
196.Xr GEOM 4 ,
197.Xr devfs 5
198.Sh AUTHORS
199This manual page was written by
200.An Robert Watson .
201