Improve contents, ruin formatting.
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Poul-Henning Kamp
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0aef5c8497
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svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=125979
@ -35,13 +35,13 @@
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.Nd Kernel disk storage API
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.Sh SYNOPSIS
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.In geom/geom_disk.h
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.Ft struct *disk
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.Fo disk_alloc
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.Fc
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.Ft void
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.Fo disk_create
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.Fa "int unit"
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.Fa "struct disk *disk"
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.Fa "int flags"
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.Fa "void *unused"
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.Fa "void *unused2"
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.Fa "int version"
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.Fc
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.Ft void
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.Fn disk_destroy "struct disk *disk"
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@ -60,33 +60,40 @@ function pointers for various methods that may be performed on the device,
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as well as private data storage for the device driver.
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In addition, some fields are reserved for use by GEOM in managing access
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to the device and its statistics.
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Because of storage driver framework private data stored in
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.Pp
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GEOM has the ownership of
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.Vt "struct disk" ,
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instances of the structure should be allocated out of writable, pre-zero'd
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memory.
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and drivers must allocate storage for it with the
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.Fn disk_alloc
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function,
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fill in the fields and call
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.Fn disk_create
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when the device is ready to service requests.
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After calling
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.Fn disk_destroy
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the device driver are not allowed to access the contents of struct disk
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any more.
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.Pp
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Public fields in the structure will generally be assumed not to change once
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the structure is submitted to
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.Fn disk_create ,
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and so no explicit locking is employed; drivers that change the values of
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any of these fields do so at their own risk.
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.Fn disk_create
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takes a second parameter
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.Va version
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which must always be passed
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.Dv DISK_VERSION .
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If GEOM detects that the driver is compiled against an unsupported version
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it will ignore the device and print a warning on the console.
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.Pp
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Memory associated with the
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.Vt "struct disk"
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is owned by the device driver, but should not be released until after
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the completion of a call to
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.Fn disk_destroy .
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.Ss Descriptive Fields
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.Pp
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The following fields identify the disk device described by the structure
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instance, and must be filled in prior to submitting the structure to
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.Fn disk_create :
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.Fn disk_create
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and may not be subsequently changed:
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.Bl -tag -width XXX
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.It Vt u_int Va d_flags
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Optional flags indicating to the storage framework what optional features
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or descriptions the storage device driver supports.
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Currently supported flags are
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.Dv DISKFLAG_NOGIANT
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.Dv DISKFLAG_NEEDSGIANT
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(maintained by device driver),
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.Dv DISKFLAG_OPEN
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(maintained by storage framework),
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@ -114,40 +121,61 @@ values will uniquely identify a disk storage device.
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The following fields identify various disk device methods, if implemented:
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.Bl -tag -width XXX
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.It Vt "disk_open_t *" Va d_open
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Invoked when the disk device is opened.
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Optional: Invoked when the disk device is opened.
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If no method is provided open will always succeed.
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.It Vt "disk_close_t *" Va d_close
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Invoked when the disk device is closed.
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Optional: Invoked when the disk device is closed.
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Although an error code may be returned, the call should always terminate
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any state setup by the corresponing open method call.
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.It Vt "disk_strategy_t *" Va d_strategy
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Invoked when a new
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Mandatory: Invoked when a new
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.Vt struct bio
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is to be initiated on the disk device.
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.It Vt "disk_ioctl_t *" Va d_ioctl
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Invoked when a I/O control operation is initiated on the disk device.
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Optional: Invoked when a I/O control operation is initiated on the disk device.
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Please note that for security reasons these operations should not
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be able to affect other devices than the one on which they are performed.
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.It Vt "dumper_t *" Va d_dump
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Invoked when a kernel crash dump is performed on the disk device.
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Optional: If configured with
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.Xr dumpon 8
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this function is invoked from a very restricted system state after a
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kernel panic to record a copy of the sytem RAM to the disk.
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.El
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.Ss Media Properties
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The following fields identify the size, layout, and other media properties
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of the disk device.
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.Ss Mandatory Media Properties
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The following fields identify the size and granularity of the disk device.
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These fields must stay stable from return of the drivers open method until
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the close method is called, but it is perfectly legal to modify them in
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the open method before returning.
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.Bl -tag -width XXX
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.It Vt u_int Va d_sectorsize
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The sectorsize of the disk device.
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The sectorsize of the disk device in bytes.
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.It Vt off_t Va d_mediasize
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The size of the disk device in bytes.
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.It Vt u_int Va d_fwsectors
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The number of sectors advertised on the disk device by the firmware or
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BIOS.
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.It Vt u_int Va d_fwheads
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The number of heads advertised on the disk device by the firmeware or
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BIOS.
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.It Vt u_int Va d_maxsize
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The maximum I/O request the disk device supports.
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The maximum supported size in bytes of I/O request.
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Requests larger than this size will be chopped up by GEOM.
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.El
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.Ss Optional Media Properties
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These optional fields can provide extra information about the disk
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device.
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Do not initialize these fields if the field/concept does not apply.
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These fields must stay stable from return of the drivers open method until
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the close method is called, but it is perfectly legal to modify them in
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the open method before returning.
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.Bl -tag -width XXX
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.It Vt u_int Va d_fwsectors
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.It Vt u_int Va d_fwheads
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The number of sectors and heads advertised on the disk device by the
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firmware or BIOS.
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These values are almost universally bogus, but on some architectures
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necessary for the correct calculation of diskpartitioning.
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.It Vt u_int Va d_stripeoffset
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If the disk device supports an optimal stripe size and offset, such as
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a RAID device, it may advertise that offset using this field.
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.It Vt u_int Va d_stripesize
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If the disk device supports an optimal stripe size and offset, such as
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a RAID device, it may advertise that size using this field.
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These two fields can be used to describe the width and location of
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natural performance boundaries for most disk technologies.
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Please see
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.Xr src/sys/geom/notes
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for details.
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.El
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.Ss Driver Private Data
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This field may be used by the device driver to store a pointer to
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@ -155,6 +183,8 @@ private data to implement the disk service.
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.Bl -tag -width XXX
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.It Vt "void *" Va d_drv1
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Private data pointer.
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Typically used to store a pointer to the drivers "softc" structure
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for this disk device.
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.El
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.Sh SEE ALSO
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.Xr GEOM 4 ,
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