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NAME | C SYNOPSIS | DESCRIPTION | SEE ALSO | DIAGNOSTICS | COLOPHON |
PMEXTRACTVALUE(3) Library Functions Manual PMEXTRACTVALUE(3)
pmExtractValue - extract a performance metric value from a pmResult
structure
#include <pcp/pmapi.h>
int pmExtractValue(int valfmt, const pmValue *ival, int itype,
pmAtomValue *oval, int otype);
cc ... -lpcp
The pmValue structure is embedded within the pmResult structure that
is used to return one or more performance metrics; see pmFetch(3).
All performance metric values may be encoded in a pmAtomValue union,
defined as follows;
typedef union {
__int32_t l; /* 32-bit signed */
__uint32_t ul; /* 32-bit unsigned */
__int64_t ll; /* 64-bit signed */
__uint64_t ull; /* 64-bit unsigned */
float f; /* 32-bit floating point */
double d; /* 64-bit floating point */
char *cp; /* char ptr */
pmValueBlock *vbp; /* pmValueBlock ptr */
} pmAtomValue;
The routine pmExtractValue provides a convenient mechanism for
extracting values from the pmValue part of a pmResult structure,
optionally converting the data type, and making the result available
to the application programmer.
itype defines the data type of the input value held in ival according
to the storage format defined by valfmt (see pmFetch(3)). otype
defines the data type of the result to be placed in oval.
The value for itype is typically extracted from a pmDesc structure,
following a call to pmLookupDesc(3) for a particular performance
metric.
The otype value should be one of the defined PM_TYPE_... values,
that have a 1:1 correspondence with the fields in the pmAtomValue
union.
Normally the valfmt parameter would be plucked from the same pmResult
structure that provides the ival parameter, and if valfmt specifies
PM_VAL_INSITU, then the following types are not allowed, as these
cannot be encoded in 32-bits; __int64_t, __uint64_t, double, char *
and void * (the corresponding itype values are PM_TYPE_64,
PM_TYPE_U64, PM_TYPE_DOUBLE, PM_TYPE_STRING, PM_TYPE_AGGREGATE and
PM_TYPE_EVENT respectively). If valfmt specifies PM_VAL_PTR, then
the value will be extracted from the associated pmValueBlock
structure, and the __int32_t, __uint32_t and float options (itype
being PM_TYPE_32, PM_TYPE_U32 and PM_TYPE_FLOAT respectively) are not
allowed, as PM_VAL_INSITU is the appropriate encoding for these.
The following table defines the various possibilities for the type
conversion -- the input type (itype) is shown vertically, and the
output type (otype) is shown horizontally. Y means the conversion is
always acceptable, N means the conversion can never be performed (the
function returns PM_ERR_CONV), P means the conversion may lose
accuracy (but no error status is returned), T means the result may be
subject to high-order truncation (in which case the function returns
PM_ERR_TRUNC) and S means the conversion may be impossible due to the
sign of the input value (in which case the function returns
PM_ERR_SIGN). If an error occurs, the value represented by oval will
be zero (or NULL).
Note that although some of the conversions involving the types
PM_TYPE_STRING and PM_TYPE_AGGREGATE are indeed possible, but are
marked N - the rationale is that pmExtractValue should not be
attempting to duplicate functionality already available in the C
library via sscanf(3) and sprintf(3).
No conversion involving the type PM_TYPE_EVENT is supported.
| 32 | U32 | 64 | U64 | FLOAT | DBLE | STRNG | AGGR | EVENT
======|=====|=======|=====|=======|=======|======|=======|======|=======
32 | Y | S | Y | S | P | P | N | N | N
U32 | T | Y | Y | Y | P | P | N | N | N
64 | T | T,S | Y | S | P | P | N | N | N
U64 | T | T | T | Y | P | P | N | N | N
FLOAT | P,T | P,T,S | P,T | P,T,S | Y | Y | N | N | N
DBLE | P,T | P,T,S | P,T | P,T,S | P | Y | N | N | N
STRNG | N | N | N | N | N | N | Y | N | N
AGGR | N | N | N | N | N | N | N | Y | N
EVENT | N | N | N | N | N | N | N | N | N
In the cases where multiple conversion errors could occur, the first
encountered error will be notified, and the order of checking is not
defined.
If the output conversion is to one of the pointer types, i.e. otype
is PM_TYPE_STRING or PM_TYPE_AGGREGATE, then the value buffer will
have been allocated by pmExtractValue(3) using malloc(3), and it is
the caller's responsibility to free the space when it is no longer
required.
Although this function appears rather complex, it has been
constructed to assist the development of performance tools that wish
to convert values, whose type is only known via the type field in a
pmDesc structure, into a canonical type for local processing. See
the pmFetchGroup functions for a simpler alternative.
PMAPI(3), pmAtomStr(3), pmConvScale(3), pmFetch(3), pmFetchGroup(3),
pmLookupDesc(3), pmPrintValue(3), pmTypeStr(3), pmUnitsStr(3) and
pmUnpackEventRecords(3).
PM_ERR_CONV
Impossible conversion, marked by N in above table
PM_ERR_TRUNC
High-order truncation occurred
PM_ERR_SIGN
Conversion of negative value to unsigned type attempted
This page is part of the PCP (Performance Co-Pilot) project.
Information about the project can be found at ⟨http://www.pcp.io/⟩.
If you have a bug report for this manual page, send it to
pcp@oss.sgi.com. This page was obtained from the project's upstream
Git repository ⟨git://git.pcp.io/pcp⟩ on 2017-07-05. If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
Performance Co-Pilot PCP PMEXTRACTVALUE(3)
Pages that refer to this page: pcpintro(3), pmapi(3), pmatomstr(3), pmconvscale(3), pmextractvalue(3), pmfetch(3), pmfetchgroup(3), pmlookupdesc(3), pmprintvalue(3), pmsemstr(3), pmtypestr(3), pmunitsstr(3)