freebsd-dev/lib/libgeom/libgeom.3

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.Dd February 8, 2003
.Dt LIBGEOM 3
.Os
.Sh NAME
.Nm geom_stats_open ,
.Nm geom_stats_close ,
.Nm geom_stats_resync ,
.Nm geom_stats_snapshot_get ,
.Nm geom_stats_snapshot_free ,
.Nm geom_stats_snapshot_timestamp ,
.Nm geom_stats_snapshot_reset ,
.Nm geom_stats_snapshot_next ,
.Nm gctl_get_handle ,
.Nm gctl_ro_param ,
.Nm gctl_rw_param ,
.Nm gctl_issue ,
.Nm gctl_free ,
.Nm gctl_dump
.Nd userland API library for kernel GEOM subsystem
.Sh LIBRARY
.Lb libgeom
.Sh SYNOPSIS
.In libgeom.h
.Ss "Statistics Functions"
.Ft void
.Fn geom_stats_close void
.Ft int
.Fn geom_stats_open void
.Ft void
.Fn geom_stats_resync void
.Ft "void *"
.Fn geom_stats_snapshot_get void
.Ft void
.Fn geom_stats_snapshot_free "void *arg"
.Ft void
.Fn geom_stats_snapshot_timestamp "void *arg" "struct timespec *tp"
.Ft void
.Fn geom_stats_snapshot_reset "void *arg"
.Ft "struct g_stat *"
.Fn geom_stats_snapshot_next "void *arg"
.Ss "Control Functions"
.Ft "struct gctl_req *"
.Fn gctl_get_handle "void"
.Ft void
.Fn gctl_ro_param "struct gctl_req *req" "const char *name" "int len" "const void *value"
.Ft void
.Fn gctl_rw_param "struct gctl_req *req" "const char *name" "int len" "void *value"
.Ft "const char *"
.Fn gctl_issue "struct gctl_req *req"
.Ft void
.Fn gctl_free "struct gctl_req *req"
.Ft void
.Fn gctl_dump "struct gctl_req *req" "FILE *f"
.Sh DESCRIPTION
The
.Nm geom
library contains the official and publicized API for
interacting with the GEOM subsystem in the kernel.
.Ss "Statistics Functions"
GEOM collects statistics data for all consumers and providers, but does
not perform any normalization or presentation on the raw data, this is
left as an excercize for user-land presentation utilities.
.Pp
The
.Fn geom_stats_open
and
.Fn geom_stats_close
functions open and close the necessary pathways to access the raw
statistics information in the kernel.
These functions are likely to
open one or more files and cache the file descriptors locally.
The
.Fn geom_stats_open
function returns zero on success, and sets
.Va errno
if not.
.Pp
The
.Fn geom_stats_resync
function will check if more statistics collection points have been
added in the kernel since
.Fn geom_stats_open
or the previous call to
.Fn geom_stats_resync .
.Pp
The
.Fn geom_stats_snapshot_get
function
will acquire a snapshot of the raw data from the kernel, and while a
reasonable effort is made to make this snapshot as atomic and consistent
as possible, no guarantee is given that it will actually be so.
The snapshot must be freed again using the
.Fn geom_stats_snapshot_free
function.
The
.Fn geom_stats_snapshot_get
function returns
.Dv NULL
on failure.
.Pp
The
.Fn geom_stats_snapshot_timestamp
function
provides access to the timestamp acquired in the snapshot.
.Pp
The
.Fn geom_stats_snapshot_reset
and
.Fn geom_stats_snapshot_next
functions
provide an iterator over the statistics slots in the snapshot.
The
.Fn geom_stats_snapshot_reset
function
forces the internal pointer in the snapshot back to before the first item.
The
.Fn geom_stats_snapshot_next
function
returns the next item, and
.Dv NULL
if there are no more items in the snapshot.
.Ss "Control Functions"
The
.Fn gctl_*
functions are used to send requests to GEOM classes.  In order for a GEOM
class to actually be able to receive these requests, it must have defined a
"ctlreq" method.
.Pp
A
.Ar struct gctl_req * ,
obtained with
.Fn gctl_get_handle ,
can hold any number of parameters, which must be added to it with
.Fn gctl_ro_param
(for read-only parameters) or
.Fn gctl_rw_param
(for read/write parameters).
.Pp
Both
.Fn gctl_ro_param
and
.Fn gctl_rw_param
take a string
.Ar name ,
which is used to identify the parameter, and a
.Ar value ,
which contains - in the read-only case - the data to be passed to the
GEOM class, or - in the read/write case - a pointer to preallocated memory
that the GEOM class should fill with the desired data.  If
.Ar len
is negative, it is assumed that
.Ar value
is an ASCII string and the actual length is taken from the string length of
.Ar value ;
otherwise it must hold the size of
.Ar value .
.Pp
A parameter with a
.Ar name
containing the string "class" is mandatory for each request, and the
corresponding
.Ar value
must hold the name of the GEOM class where the request should be sent to.
.Pp
Also mandatory for each request is a parameter with a
.Ar name
called "verb", and the corresponding
.Ar value
needs to hold the command string that the GEOM class should react upon.
.Pp
Once all desired parameters are filled in, the request must be sent to
the GEOM subsystem with
.Fn gctl_issue ,
which returns NULL on success, or a string containing the error message
on failure.
.Pp
After the request is finished, the allocated memory should be released with
.Fn gctl_free .
.Pp
.Fn gctl_dump
can be used to format the contents of
.Ar req
to the open file handle pointed to by
.Ar f 
for debugging purposes.
.Pp
Error handling for the control functions is postponed until the call
to 
.Fn gctl_issue
which returns NULL on success or an error message corresponding to the
first error which happened.
.Sh EXAMPLES
Create a request that is to be sent to the CCD class and tell
it to destroy a specific geom:
.Bd -literal -offset indent
H = gctl_get_handle();
gctl_ro_param(H, "verb", -1, "destroy geom");
gctl_ro_param(H, "class", -1, "CCD");
sprintf(buf, "ccd%d", ccd);
gctl_ro_param(H, "geom", -1, buf);
errstr = gctl_issue(H);
if (errstr != NULL)
    err(1, "Could not destroy ccd: %s", errstr);
gctl_free(H);
.Ed
.Sh SEE ALSO
.Rs
http://ezine.daemonnews.org/200308/blueprints.html
.Re
.Sh HISTORY
The
.Nm geom
library appeared in
.Fx 5.1 .
.Sh AUTHORS
.An Poul-Henning Kamp Aq phk@FreeBSD.org
.An Lukas Ertl Aq le@FreeBSD.org