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If after extracting stats arguments and group tags nothing remains
of aux_data but '-' set the region->aux_data field to the empty
string to match behaviour for non-grouped regions.
Although not harmful do not allow a group containing regions with
histograms since it is not currently possible to present histogram
data aggregated for the group.
Although a non-zero value for the number of ticks spent doing IO
should imply a non-zero number of IOs in the interval test for
this explicitly to avoid a divide-by-zero in the event of bad
counter data.
It's possible for interval_ns to be zero if the interval is not
set or the clock is misconfigured. Test for this before using the
value as the divisor in the utilisation calculation.
Walk flags are ULL constants; cast the result to a uint64_t before
logging with a FMTx64 format specifier to avoid a compiler warning:
warning: format ‘%lx’ expects argument of type ‘long unsigned int’,
but argument 5 has type ‘long long unsigned int’
Make it clear in libdevmapper.h, and in function argument names, that
libdm-stats uses the aux_data field internally and that any values set
for user_data are appended to the library values before being stored
with a region, and similarly, that internal data fields will be stripped
prior to returning any previously stored user_data.
Add support do dm_stats_walk*() to walk over the set of
available groups using the cursor embedded in the dm_stats
handle, and to obtain the type of the object at the current
stats cursor location. A set of flags is introduced to
control which objects are visited:
DM_STATS_WALK_AREA
DM_STATS_WALK_REGION
DM_STATS_WALK_GROUP
DM_STATS_WALK_ALL
A final flag suppresses visits to regions that contain only a
single area - since the aggregate of such a region is idential
to the area it contains this allows these duplicates to be
filtered out:
DM_STATS_WALK_SKIP_SINGLE_AREA
If flags are not initialised before beginning a walk the default
set matches the behaviour of previous versions of the library.
Also accept group identifiers as immediate arguments to the
counter, metric, and property functions by adding control
flags to the region and area identifiers passed in.
Region and area properties are mapped to their equivalents for
the group (for example: group size is reported as the sum of
all regions contained in the group). Counter and metric values
are aggregated for the region or group.
Introduce constants for the buffer sizes that libdm-stats uses:
one for messages sent to the kernel, one for rows of response data
returned, and a pair for the "start+len" range and histogram bounds
strings.
Add a grouping facility to the libdm-stats library that allows the
user to bind several regions together as a group. Groups may be
used to aggregate data from several regions for reporting, or to
select and sort among large sets of regions.
A textual descriptor ("group tag") is associated with each group
and is stored in the first group member's aux_data field. The
tag contains the group member list and an optional alias for the
group, allowing the user to assign meaningful names to groups of
regions.
These descriptors are parsed in @stats_list message responses and
populate the resulting region and area tables with the group
structure.
Groups with overlapping regions are permitted but since this will
result in some events being counted more than once a warning is
printed in this case.
Nested and overlapping groups are not currently supported and
attempting to create these configurations results in error.
Add a new enum based interface for accessing counter and metric
values that uses a single function for each:
uint64_t dm_stats_get_counter(const struct dm_stats *dms,
dm_stats_counter_t counter
uint64_t region_id, uint64_t area_id);
int dm_stats_get_metric(const struct dm_stats *dms, int metric,
uint64_t region_id, uint64_t area_id,
double *value);
This simplifies the implementation of value aggregation for
groups of regions. The named function interface now calls the
enum interface internally so that all new functionality is
available regardless of the method used to retrieve values.
Cache the device-mapper name of a bound device in the dm_stats
handle.
This will be used by stats groups to report a device name or
user defined alias for groups.
The device-mapper name, device numbers and uuid stored in the
dm_stats handle are used only to bind the handle to a specific
device in order to issue ioctls.
Rename them to "bind_*" to reflect this usage in preparation
for caching the device-mapper name of the bound device in the
dm_stats handle.
This will be used to allow optional aliases to be set for
dmstats groups.
Check that @stats_list and @stats_print returned data in the
_stats_parse_list() and _stats_parse_region() functions before
attempting to operate on region and area values.
This avoids a coverity warning since fgets() could potentially
return no data from the memory buffer returned by the ioctl.
In both cases the ioctl would return an error, preventing these
functions from running, however it is cleaner to test for the
condition explicitly and fail in those cases.
Split up _build_histogram_arg() into separate functions to allocate
and fill the histogram arg string and remove nested local variable
declarations from the parent function.
Coverity flags a user-after-free in _stats_histograms_destroy():
>>> Calling "dm_pool_free" frees pointer "mem->chunk" which has
>>> already been freed.
This should not be possible since the histograms are destroyed in
reverse order of allocation:
203 for (n = _nr_areas_region(region) - 1; n; n--)
204 if (region->counters[n].histogram)
205 dm_pool_free(mem, region->counters[n].histogram);
It appears that Coverity is unaware that pool->chunk is updated
during the call to dm_pool_free() and valgrind flags no errors in
this function when called with multiple allocated histograms.
Since there is no actual need to free the histograms individually
in this way simplify the code and just free the first allocated
object (which will also free all later allocated histograms in a
single call).
The histogram changes adds a new error path to dm_stats_create().
Make sure that the dm_stats handle is properly destroyed if we fail
to create the histogram pool and check for failures setting the
program_id.
Since we are growing an object in the histogram pool the return
value of dm_pool_grow_object() must be checked and error paths need
to abandon the object before returning.
Older versions of gcc aren't able to track the assignments of
local variables as well as the latest versions leading to spurious
warnings like:
libdm-stats.c:2183: warning: "len" may be used uninitialized in this
function
libdm-stats.c:2177: warning: "minwidth" may be used uninitialized in
this function
Both of these variables are in fact assigned in all possible paths
through the function and later compilers do not produce these
warnings.
There's no reason to not initialize these variables though and
it makes the function slightly easier to follow.
Also fix one use of 'unsigned' for a nr_bins value.
Add support for creating, parsing, and reporting dm-stats latency
histograms on kernels that support precise_timestamps.
Histograms are specified as a series of time values that give the
boundaries of the bins into which I/O counts accumulate (with
implicit lower and upper bounds on the first and last bins).
A new type, struct dm_histogram, is introduced to represent
histogram values and bin boundaries.
The boundary values may be given as either a string of values (with
optional unit suffixes) or as a zero terminated array of uint64_t
values expressing boundary times in nanoseconds.
A new bounds argument is added to dm_stats_create_region() which
accepts a pointer to a struct dm_histogram initialised with bounds
values.
Histogram data associated with a region is parsed during a call to
dm_stats_populate() and used to build a table of histogram values
that are pointed to from the containing area's counter set. The
histogram for a specified area may then be obtained and interogated
for values and properties.
This relies on kernel support to provide the boundary values in
a @stats_list response: this will be present in 4.3 and 4.2-stable. A
check for a minimum driver version of 4.33.0 is implemented to ensure
that this is present (4.32.0 has the necessary precise_timestamps and
histogram features but is unable to report these via @stats_list).
Access methods are provided to retrieve histogram values and bounds
as well as simple string representations of the counts and bin
boundaries. Methods are also available to return the total count
for a histogram and the relative value (as a dm_percent_t) of a
specified bin.
Add support for the kernel precise_timestamps feature. This allows
regions to be created using counters with nanosecond precision.
A new dm_stats method, dm_stats_set_precise_timestamps() causes all
future regions created with this handle to attempt to enable precise
counters.
Several interfaced in libdm-stats return a uint64_t when it is
only used to signal success/failure: change all these uses to
return a simple int instead.
