DISK_INIT(9) FreeBSD Kernel Developer's Manual DISK_INIT(9)
NAME
disk_init, disk_attach, disk_detach, disk_busy, disk_unbusy - generic
disk framework
SYNOPSIS
#include <sys/types.h>
#include <sys/disklabel.h>
#include <sys/disk.h>
void
disk_init(void);
void
disk_attach(struct disk *);
void
disk_detach(struct disk *);
void
disk_busy(struct disk *);
void
disk_unbusy(struct disk *, long bcount, int read);
DESCRIPTION
The OpenBSD generic disk framework is designed to provide flexible,
scalable, and consistent handling of disk state and metrics information.
The fundamental component of this framework is the disk_init structure,
which is defined as follows:
struct disk {
TAILQ_ENTRY(disk) dk_link; /* link in global disklist */
struct rwlock dk_lock; /* disk lock */
struct mutex dk_mtx; /* busy/unbusy mtx */
char *dk_name; /* disk name */
struct device *dk_device; /* disk device structure. */
dev_t dk_devno; /* disk device number. */
int dk_flags; /* disk flags */
#define DKF_CONSTRUCTED 0x0001
#define DKF_OPENED 0x0002
#define DKF_NOLABELREAD 0x0004
/*
* Metrics data; note that some metrics may have no meaning
* on certain types of disks.
*/
int dk_busy; /* busy counter */
u_int64_t dk_rxfer; /* total number of read transfers */
u_int64_t dk_wxfer; /* total number of write transfers */
u_int64_t dk_seek; /* total independent seek operations */
u_int64_t dk_rbytes; /* total bytes read */
u_int64_t dk_wbytes; /* total bytes written */
struct timeval dk_attachtime; /* time disk was attached */
struct timeval dk_timestamp; /*time of first busy or any unbusy*/
struct timeval dk_time; /* total time spent busy */
int dk_bopenmask; /* block devices open */
int dk_copenmask; /* character devices open */
int dk_openmask; /* composite (bopen|copen) */
int dk_state; /* label state ### */
int dk_blkshift; /*shift to convert DEV_BSIZE to blks*/
int dk_byteshift; /* shift to convert bytes to blks */
/*
* Disk label information. Storage for the in-core disk label
* must be dynamically allocated, otherwise the size of this
* structure becomes machine-dependent.
*/
struct disklabel *dk_label;
};
The system maintains a global linked-list of all disks attached to the
system. This list, called disklist, may grow or shrink over time as
disks are dynamically added and removed from the system. An example of a
driver which currently makes use of the detachment capability of the
framework is the vnd(4) pseudo-device driver.
The following is a brief description of each function in the framework:
disk_init() Initialize the disklist and other data structures used by
the framework. Called by main() before autoconfiguration.
disk_attach() Attach a disk; allocate storage for the disklabel, set the
"attached time" timestamp, insert the disk into the
disklist, and increment the system disk count.
disk_detach() Detach a disk; free storage for the disklabel, remove the
disk from the disklist, and decrement the system disk
count. If the count drops below zero, panic.
disk_busy() Increment the disk's "busy counter". If this counter goes
from 0 to 1, set the timestamp corresponding to this
transfer.
disk_unbusy() Decrement a disk's busy counter. If the count drops below
zero, print a warning message. Get the current time,
subtract it from the disk's timestamp, and add the
difference to the disk's running total. Set the disk's
timestamp to the current time. If the provided byte count
is greater than 0, add it to the disk's running total and
increment the number of transfers performed by the disk.
The third argument read specifies the direction of I/O; if
non-zero it means reading from the disk, otherwise it
means writing to the disk.
The functions typically called by device drivers are disk_attach(),
disk_detach(), disk_busy() and disk_unbusy().
USING THE FRAMEWORK
This section includes a description on basic use of the framework and
example usage of its functions. Actual implementation of a device driver
which utilizes the framework may vary.
A special routine, disk_init(), is provided to perform basic
initialization of data structures used by the framework. It is called
exactly once by the system, in main(), before device autoconfiguration.
Each device in the system uses a "softc" structure which contains
autoconfiguration and state information for that device. In the case of
disks, the softc should also contain one instance of the disk structure,
e.g.:
struct foo_softc {
struct device *sc_dev; /* generic device information */
struct disk *sc_dk; /* generic disk information */
[ . . . more . . . ]
};
In order for the system to gather metrics data about a disk, the disk
must be registered with the system. The disk_attach() routine performs
all of the functions currently required to register a disk with the
system including allocation of disklabel storage space, recording of the
time since boot that the disk was attached, and insertion into the
disklist. Note that since this function allocates storage space for the
disklabel, it must be called before the disklabel is read from the media
or used in any other way. Before disk_attach() is called, a portion of
the disk structure must be initialized with data specific to that disk.
For example, in the "foo" disk driver, the following would be performed
in the autoconfiguration "attach" routine:
void
fooattach(struct device *parent, struct device *self, void *aux)
{
struct foo_softc *sc = (struct foo_softc *)self;
[ . . . ]
/* Initialize and attach the disk structure. */
sc->sc_dk.dk_driver = &foodkdriver;
sc->sc_dk.dk_name = sc->sc_dev.dv_xname;
disk_attach(&sc->sc_dk);
/* Read geometry and fill in pertinent parts of disklabel. */
[ . . . ]
}
The foodkdriver above is the disk's "driver" switch. This switch
currently includes a pointer to the disk's "strategy" routine. This
switch needs to have global scope and should be initialized as follows:
void foostrategy(struct buf *);
struct dkdriver foodkdriver = { foostrategy };
Once the disk is attached, metrics may be gathered on that disk. In
order to gather metrics data, the driver must tell the framework when the
disk starts and stops operations. This functionality is provided by the
disk_busy() and disk_unbusy() routines. The disk_busy() routine should
be called immediately before a command to the disk is sent, e.g.:
void
foostart(struct foo_softc *sc)
{
[ . . . ]
/* Get buffer from drive's transfer queue. */
[ . . . ]
/* Build command to send to drive. */
[ . . . ]
/* Tell the disk framework we're going busy. */
disk_busy(&sc->sc_dk);
/* Send command to the drive. */
[ . . . ]
}
When disk_busy() is called, a timestamp is taken if the disk's busy
counter moves from 0 to 1, indicating the disk has gone from an idle to
non-idle state. Note that disk_busy() must be called at splbio(). At
the end of a transaction, the disk_unbusy() routine should be called.
This routine performs some consistency checks, such as ensuring that the
calls to disk_busy() and disk_unbusy() are balanced. This routine also
performs the actual metrics calculation. A timestamp is taken, and the
difference from the timestamp taken in disk_busy() is added to the disk's
total running time. The disk's timestamp is then updated in case there
is more than one pending transfer on the disk. A byte count is also
added to the disk's running total, and if greater than zero, the number
of transfers the disk has performed is incremented.
void
foodone(struct foo_xfer *xfer)
{
struct foo_softc = (struct foo_softc *)xfer->xf_softc;
struct buf *bp = xfer->xf_buf;
long nbytes;
[ . . . ]
/*
* Get number of bytes transferred. If there is no buf
* associated with the xfer, we are being called at the
* end of a non-I/O command.
*/
if (bp == NULL)
nbytes = 0;
else
nbytes = bp->b_bcount - bp->b_resid;
[ . . . ]
/* Notify the disk framework that we've completed the transfer. */
disk_unbusy(&sc->sc_dk, nbytes);
[ . . . ]
}
Like disk_busy(), disk_unbusy() must be called at splbio().
CODE REFERENCES
The disk framework itself is implemented within the file
sys/kern/subr_disk.c. Data structures and function prototypes for the
framework are located in sys/sys/disk.h.
The OpenBSD machine-independent SCSI disk and CD-ROM drivers utilize the
disk framework. They are located in sys/scsi/sd.c and sys/scsi/cd.c.
The OpenBSD vnd(4) driver utilizes the detachment capability of the
framework. This is located in sys/dev/vnd.c.
SEE ALSO
vnd(4), spl(9)
HISTORY
The OpenBSD generic disk framework first appeared in NetBSD 1.2.
AUTHORS
The OpenBSD generic disk framework was architected and implemented within
NetBSD by Jason R. Thorpe <
[email protected]>.
FreeBSD 14.1-RELEASE-p8 September 7, 2022 FreeBSD 14.1-RELEASE-p8