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IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR .\" ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" $FreeBSD$ .\" .Dd December 2, 2019 .Dt STATS 3 .Os .Sh NAME .Nm stats .Nd statistics gathering .Sh LIBRARY .Lb libstats .Sh SYNOPSIS .In sys/arb.h .In sys/qmath.h .In sys/stats.h .Ss Stats Blob Template Management Functions .Ft int .Fo stats_tpl_alloc .Fa "const char *name" .Fa "uint32_t flags" .Fc .Ft int .Fo stats_tpl_fetch_allocid .Fa "const char *name" .Fa "uint32_t hash" .Fc .Ft int .Fo stats_tpl_fetch .Fa "int tpl_id" .Fa "struct statsblob_tpl **tpl" .Fc .Ft int .Fo stats_tpl_id2name .Fa "uint32_t tpl_id" .Fa "char *buf" .Fa "size_t len" .Fc .Ft int .Fo stats_tpl_sample_rates .Fa "SYSCTL_HANDLER_ARGS" .Fc .Ft int .Fo stats_tpl_sample_rollthedice .Fa "struct stats_tpl_sample_rate *rates" .Fa "int nrates" .Fa "void *seed_bytes" .Fa "size_t seed_len" .Fc .Ft struct voistatspec .Fo STATS_VSS_SUM .Fc .Ft struct voistatspec .Fo STATS_VSS_MAX .Fc .Ft struct voistatspec .Fo STATS_VSS_MIN .Fc .Ft struct voistatspec .Fo STATS_VSS_CRHIST<32|64>_LIN .Fa "lb" .Fa "ub" .Fa "stepinc" .Fa "vsdflags" .Fc .Ft struct voistatspec .Fo STATS_VSS_CRHIST<32|64>_EXP .Fa "lb" .Fa "ub" .Fa "stepbase" .Fa "stepexp" .Fa "vsdflags" .Fc .Ft struct voistatspec .Fo "STATS_VSS_CRHIST<32|64>_LINEXP" .Fa "lb" .Fa "ub" .Fa "nlinsteps" .Fa "stepbase" .Fa "vsdflags" .Fc .Ft struct voistatspec .Fo "STATS_VSS_CRHIST<32|64>_USR" .Fa Sy "HBKTS" Ns Pq Sy "CRBKT" Ns ( Em "lb" ) , "..." Pc , .Fa "vsdflags" .Fc .Ft struct voistatspec .Fo "STATS_VSS_DRHIST<32|64>_USR" .Fa Sy "HBKTS" Ns Pq Sy "DRBKT" Ns ( Em "lb" , "ub" ) , "..." Pc , .Fa "vsdflags" .Fc .Ft struct voistatspec .Fo "STATS_VSS_DVHIST<32|64>_USR" .Fa Sy "HBKTS" Ns Pq Sy "DVBKT" Ns ( Em "val" ) , "..." Pc , .Fa "vsdflags" .Fc .Ft struct voistatspec .Fo STATS_VSS_TDGSTCLUST<32|64> .Fa "nctroids" .Fa "prec" .Fc .Ft int .Fo stats_tpl_add_voistats .Fa "uint32_t tpl_id" .Fa "int32_t voi_id" .Fa "const char *voi_name" .Fa "enum vsd_dtype voi_dtype" .Fa "uint32_t nvss" .Fa "struct voistatspec *vss" .Fa "uint32_t flags" .Fc .Ss Stats Blob Data Gathering Functions .Ft int .Fo stats_voi_update__ .Fa "struct statsblob *sb" .Fa "int32_t voi_id" .Fa " voival" .Fc .Ss Stats Blob Utility Functions .Ft struct statsblob * .Fo stats_blob_alloc .Fa "uint32_t tpl_id" .Fa "uint32_t flags" .Fc .Ft int .Fo stats_blob_init .Fa "struct statsblob *sb" .Fa "uint32_t tpl_id" .Fa "uint32_t flags" .Fc .Ft int .Fo stats_blob_clone .Fa "struct statsblob **dst" .Fa "size_t dstmaxsz" .Fa "struct statsblob *src" .Fa "uint32_t flags" .Fc .Ft void .Fo stats_blob_destroy .Fa "struct statsblob *sb" .Fc .Ft int .Fo stats_voistat_fetch_dptr .Fa "struct statsblob *sb" .Fa "int32_t voi_id" .Fa "enum voi_stype stype" .Fa "enum vsd_dtype *retdtype" .Fa "struct voistatdata **retvsd" .Fa "size_t *retvsdsz" .Fc .Ft int .Fo stats_voistat_fetch_ .Fa "struct statsblob *sb" .Fa "int32_t voi_id" .Fa "enum voi_stype stype" .Fa " *ret" .Fc .Ft int .Fo stats_blob_snapshot .Fa "struct statsblob **dst" .Fa "size_t dstmaxsz" .Fa "struct statsblob *src" .Fa "uint32_t flags" .Fc .Ft int .Fo stats_blob_tostr .Fa "struct statsblob *sb" .Fa "struct sbuf *buf" .Fa "enum sb_str_fmt fmt" .Fa "uint32_t flags" .Fc .Ft int .Fo stats_voistatdata_tostr .Fa "const struct voistatdata *vsd" .Fa "enum vsd_dtype dtype" .Fa "enum sb_str_fmt fmt" .Fa "struct sbuf *buf" .Fa "int objdump" .Fc .Ft typedef int .Fn "\*(lp*stats_blob_visitcb_t\*(rp" "struct sb_visit *sbv" "void *usrctx" .Ft int .Fo stats_blob_visit .Fa "struct statsblob *sb" .Fa "stats_blob_visitcb_t func" .Fa "void *usrctx" .Fc .Sh DESCRIPTION The .Nm framework facilitates real-time kernel and user space statistics gathering. The framework is built around the .Dq statsblob , an object embedded within a contiguous memory allocation that is mostly opaque to consumers and stores all required state. A .Dq statsblob object can itself be embedded within other objects either directly or indirectly using a pointer. .Pp Objects or subsystems for which statistics are to be gathered are initialized from a template .Dq statsblob , which acts as the blueprint for an arbitrary set of Variables Of Interest (VOIs) and their associated statistics. Each template defines a schema plus associated metadata, which are kept separate to minimize the memory footprint of blobs. .Pp Data gathering hook functions added at appropriate locations within the code base of interest feed VOI data into the framework for processing. .Pp Each .Dq statsblob , consists of a .Vt struct statsblob header and opaque internal blob structure per the following diagram: .Bd -literal -offset indent --------------------------------------------------------- | struct | uint8_t | | statsblob | opaque[] | --------------------------------------------------------- .Ed .Pp The publicly visible 8-byte header is defined as: .Bd -literal -offset indent struct statsblob { uint8_t abi; uint8_t endian; uint16_t flags; uint16_t maxsz; uint16_t cursz; uint8_t opaque[]; }; .Ed .Pp .Va abi specifies which API version the blob's .Va opaque internals conform to .Pq Dv STATS_ABI_V1 is the only version currently defined . .Va endian specifies the endianness of the blob's fields .Po .Dv SB_LE for little endian, .Dv SB_BE for big endian, or .Dv SB_UE for unknown endianness .Pc . .Va cursz specifies the size of the blob, while .Va maxsz specifies the size of the underlying memory allocation in which the blob is embedded. Both .Va cursz and .Va maxsz default to units of bytes, unless a flag is set in .Va flags that dictates otherwise. .Pp Templates are constructed by associating arbitrary VOI IDs with a set of statistics, where each statistic is specified using a .Vt struct voistatspec per the definition below: .Bd -literal -offset indent struct voistatspec { vss_hlpr_fn hlpr; struct vss_hlpr_info *hlprinfo; struct voistatdata *iv; size_t vsdsz; uint32_t flags; enum vsd_dtype vs_dtype : 8; enum voi_stype stype : 8; }; .Ed .Pp It is generally expected that consumers will not work with .Vt struct voistatspec directly, and instead use the .Fn STATS_VSS_* helper macros. .Pp The .Nm framework offers the following statistics for association with VOIs: .Bl -tag -width ".Dv VS_STYPE_TDGST" .It Dv VS_STYPE_SUM The sum of VOI values. .It Dv VS_STYPE_MAX The maximum VOI value. .It Dv VS_STYPE_MIN The minimum VOI value. .It Dv VS_STYPE_HIST A static bucket histogram of VOI values, including a count of .Dq out-of-band/bucket Dc values which did not match any bucket. Histograms can be specified as .Dq Em C Ns ontinuous Em R Ns ange Dc .Pq CRHIST Pc , .Dq Em D Ns iscrete Em R Ns ange Dc .Pq DRHIST Pc or .Dq Em D Ns iscrete Em V Ns alue Dc .Pq DVHIST Pc , with 32 or 64 bit bucket counters, depending on the VOI semantics. .It Dv VS_STYPE_TDGST A dynamic bucket histogram of VOI values based on the t-digest method .Po refer to the t-digest paper in the .Sx SEE ALSO section below .Pc . .El .Pp A .Dq visitor software design pattern Ns -like scheme is employed to facilitate iterating over a blob's data without concern for the blob's structure. The data provided to visitor callback functions is encapsulated in .Vt struct sb_visit per the definition below: .Bd -literal -offset indent struct sb_visit { struct voistatdata *vs_data; uint32_t tplhash; uint32_t flags; int16_t voi_id; int16_t vs_dsz; enum vsd_dtype voi_dtype : 8; enum vsd_dtype vs_dtype : 8; int8_t vs_stype; uint16_t vs_errs; }; .Ed .Pp The .Fn stats_tpl_sample_rates and .Fn stats_tpl_sample_rollthedice functions utilize .Vt struct stats_tpl_sample_rate to encapsulate per-template sample rate information per the definition below: .Bd -literal -offset indent struct stats_tpl_sample_rate { int32_t tpl_slot_id; uint32_t tpl_sample_pct; }; .Ed .Pp The .Va tpl_slot_id member holds the template's slot ID obtained from .Fn stats_tpl_alloc or .Fn stats_tpl_fetch_allocid . The .Va tpl_sample_pct member holds the template's sample rate as an integer percentage in the range [0,100]. .Pp The .Vt stats_tpl_sr_cb_t conformant function pointer that is required as the .Fa arg1 of .Fn stats_tpl_sample_rates is defined as: .Bd -literal -offset indent enum stats_tpl_sr_cb_action { TPL_SR_UNLOCKED_GET, TPL_SR_RLOCKED_GET, TPL_SR_RUNLOCK, TPL_SR_PUT }; typedef int (*stats_tpl_sr_cb_t)(enum stats_tpl_sr_cb_action action, struct stats_tpl_sample_rate **rates, int *nrates, void *ctx); .Ed .Pp It is required that a conformant function: .Bl -dash .It Return an appropriate .Xr errno 2 on error, otherwise 0. .It When called with .Qq action == TPL_SR_*_GET , return the subsystem's rates list ptr and count, locked or unlocked as requested. .It When called with .Qq action == TPL_SR_RUNLOCK , unlock the subsystem's rates list ptr and count. Pair with a prior .Qq action == TPL_SR_RLOCKED_GET call. .It When called with .Qq action == TPL_SR_PUT , update the subsystem's rates list ptr and count to the sysctl processed values and return the inactive list details in .Fa rates and .Fa nrates for garbage collection by .Fn stats_tpl_sample_rates . .El .Pp Where templates need to be referenced via textual means, for example via a MIB variable, the following string based template spec formats can be used: .Bl -enum .It .Qq Qc Ns : .Ns , for example .Qq TCP_DEFAULT Qc Ns :1731235399 .It .Qq Qc .Ns , for example .Qq TCP_DEFAULT Qc .It : .Ns , for example :1731235399 .El .Pp The first form is the normative spec format generated by the framework, while the second and third forms are convenience formats primarily for user input. The use of inverted commas around the template name is optional. .Ss MIB Variables The in-kernel .Nm framework exposes the following framework-specific variables in the .Va kern.stats branch of the .Xr sysctl 3 MIB. .Bl -tag -width "templates" .It templates Read-only CSV list of registered templates in normative template spec form. .El .Ss Template Management Functions The .Fn stats_tpl_alloc function allocates a new template with the specified unique name and returns its runtime-stable template slot ID for use with other API functions. The .Fa flags argument is currently unused. .Pp The .Fn stats_tpl_fetch_allocid function returns the runtime-stable template slot ID of any registered template matching the specified name and hash. .Pp The .Fn stats_tpl_fetch function returns the pointer to the registered template object at the specified template slot ID. .Pp The .Fn stats_tpl_id2name function returns the name of the registered template object at the specified template slot ID. .Pp The .Fn stats_tpl_sample_rates function provides a generic handler for template sample rates management and reporting via .Xr sysctl 3 MIB variables. Subsystems can use this function to create a subsystem-specific .Xr SYSCTL_PROC 9 MIB variable that manages and reports subsystem-specific template sampling rates. Subsystems must supply a .Vt stats_tpl_sr_cb_t conformant function pointer as the sysctl's .Fa arg1 , which is a callback used to interact with the subsystem's stats template sample rates list. Subsystems can optionally specify the sysctl's .Fa arg2 as non-zero, which causes a zero-initialized allocation of arg2-sized contextual memory to be heap-allocated and passed in to all subsystem callbacks made during the operation of .Fn stats_tpl_sample_rates . .Pp The .Fn stats_tpl_sample_rollthedice function makes a weighted random template selection from the supplied array of template sampling rates. The cumulative percentage of all sampling rates should not exceed 100. If no seed is supplied, a PRNG is used to generate a true random number so that every selection is independent. If a seed is supplied, selection will be made randomly across different seeds, but deterministically given the same seed. .Pp The .Fn stats_tpl_add_voistats function is used to add a VOI and associated set of statistics to the registered template object at the specified template slot ID. The set of statistics is passed as an array of .Vt struct voistatspec which can be initialized using the .Fn STATS_VSS_* helper macros or manually for non-standard use cases. For static .Fa vss arrays, the .Fa nvss count of array elements can be determined by passing .Fa vss to the .Fn NVSS macro. The .Dv SB_VOI_RELUPDATE flag can be passed to configure the VOI for use with .Fn stats_voi_update_rel_ , which entails maintaining an extra 8 bytes of state in the blob at each update. .Ss Data Gathering Functions The .Fn stats_voi_update_abs_ and .Fn stats_voi_update_rel_ functions both update all the statistics associated with the VOI identified by .Fa voi_id . The .Dq abs call uses .Fa voival as an absolute value, whereas the .Dq rel call uses .Fa voival as a value relative to that of the previous update function call, by adding it to the previous value and using the result for the update. Relative updates are only possible for VOIs that were added to the template with the .Dv SB_VOI_RELUPDATE flag specified to .Fn stats_tpl_add_voistats . .Ss Utility Functions The .Fn stats_blob_alloc function allocates and initializes a new blob based on the registered template object at the specified template slot ID. .Pp The .Fn stats_blob_init function initializes a new blob in an existing memory allocation based on the registered template object at the specified template slot ID. .Pp The .Fn stats_blob_clone function duplicates the .Fa src blob into .Fa dst , leaving only the .Va maxsz field of .Fa dst untouched. The .Dv SB_CLONE_ALLOCDST flag can be passed to instruct the function to allocate a new blob of appropriate size into which to clone .Fa src , storing the new pointer in .Fa *dst . The .Dv SB_CLONE_USRDSTNOFAULT or .Dv SB_CLONE_USRDST flags can be set to respectively signal that .Xr copyout_nofault 9 or .Xr copyout 9 should be used because .Fa *dst is a user space address. .Pp The .Fn stats_blob_snapshot function calls .Fn stats_blob_clone to obtain a copy of .Fa src and then performs any additional functions required to produce a coherent blob snapshot. The flags interpreted by .Fn stats_blob_clone also apply to .Fn stats_blob_snapshot . Additionally, the .Dv SB_CLONE_RSTSRC flag can be used to effect a reset of the .Fa src blob's statistics after a snapshot is successfully taken. .Pp The .Fn stats_blob_destroy function destroys a blob previously created with .Fn stats_blob_alloc , .Fn stats_blob_clone or .Fn stats_blob_snapshot . .Pp The .Fn stats_blob_visit function allows the caller to iterate over the contents of a blob. The callback function .Fa func is called for every VOI and statistic in the blob, passing a .Vt struct sb_visit and the user context argument .Fa usrctx to the callback function. The .Fa sbv passed to the callback function may have one or more of the following flags set in the .Va flags struct member to provide useful metadata about the iteration: .Dv SB_IT_FIRST_CB , .Dv SB_IT_LAST_CB , .Dv SB_IT_FIRST_VOI , .Dv SB_IT_LAST_VOI , .Dv SB_IT_FIRST_VOISTAT , .Dv SB_IT_LAST_VOISTAT , .Dv SB_IT_NULLVOI and .Dv SB_IT_NULLVOISTAT . Returning a non-zero value from the callback function terminates the iteration. .Pp The .Fn stats_blob_tostr renders a string representation of a blob into the .Xr sbuf 9 .Fa buf . Currently supported render formats are .Dv SB_STRFMT_FREEFORM and .Dv SB_STRFMT_JSON . The .Dv SB_TOSTR_OBJDUMP flag can be passed to render version specific opaque implementation detail for debugging or string-to-binary blob reconstruction purposes. The .Dv SB_TOSTR_META flag can be passed to render template metadata into the string representation, using the blob's template hash to lookup the corresponding template. .Pp The .Fn stats_voistatdata_tostr renders a string representation of an individual statistic's data into the .Xr sbuf 9 .Fa buf . The same render formats supported by the .Fn stats_blob_tostr function can be specified, and the .Fa objdump boolean has the same meaning as the .Dv SB_TOSTR_OBJDUMP flag. .Pp The .Fn stats_voistat_fetch_dptr function returns an internal blob pointer to the specified .Fa stype statistic data for the VOI .Fa voi_id . The .Fn stats_voistat_fetch_ functions are convenience wrappers around .Fn stats_voistat_fetch_dptr to perform the extraction for simple data types. .Sh IMPLEMENTATION NOTES The following notes apply to STATS_ABI_V1 format statsblobs. .Ss Space-Time Complexity Blobs are laid out as three distinct memory regions following the header: .Bd -literal -offset indent ------------------------------------------------------ | struct | struct | struct | struct | | statsblobv1 | voi [] | voistat [] | voistatdata [] | ------------------------------------------------------ .Ed .Pp Blobs store VOI and statistic blob state .Po 8 bytes for .Vt struct voi and 8 bytes for .Vt struct voistat respectively .Pc in sparse arrays, using the .Fa voi_id and .Vt enum voi_stype as array indices. This allows O(1) access to any voi/voistat pair in the blob, at the expense of 8 bytes of wasted memory per vacant slot for templates which do not specify contiguously numbered VOIs and/or statistic types. Data storage for statistics is only allocated for non-vacant slot pairs. .Pp To provide a concrete example, a blob with the following specification: .Bl -dash .It Two VOIs; ID 0 and 2; added to the template in that order .It VOI 0 is of data type .Vt int64_t , is configured with .Dv SB_VOI_RELUPDATE to enable support for relative updates using .Fn stats_voi_update_rel_ , and has a .Dv VS_STYPE_MIN statistic associated with it. .It VOI 2 is of data type .Vt uint32_t with .Dv VS_STYPE_SUM and .Dv VS_STYPE_MAX statistics associated with it. .El .Pp would have the following memory layout: .Bd -literal -------------------------------------- | header | struct statsblobv1, 32 bytes |------------------------------------| | voi[0] | struct voi, 8 bytes | voi[1] (vacant) | struct voi, 8 bytes | voi[2] | struct voi, 8 bytes |------------------------------------| | voi[2]voistat[VOISTATE] (vacant) | struct voistat, 8 bytes | voi[2]voistat[SUM] | struct voistat, 8 bytes | voi[2]voistat[MAX] | struct voistat, 8 bytes | voi[0]voistat[VOISTATE] | struct voistat, 8 bytes | voi[0]voistat[SUM] (vacant) | struct voistat, 8 bytes | voi[0]voistat[MAX] (vacant) | struct voistat, 8 bytes | voi[0]voistat[MIN] | struct voistat, 8 bytes |------------------------------------| | voi[2]voistat[SUM]voistatdata | struct voistatdata_int32, 4 bytes | voi[2]voistat[MAX]voistatdata | struct voistatdata_int32, 4 bytes | voi[0]voistat[VOISTATE]voistatdata | struct voistatdata_numeric, 8 bytes | voi[0]voistat[MIN]voistatdata | struct voistatdata_int64, 8 bytes -------------------------------------- TOTAL 136 bytes .Ed .Pp When rendered to string format using .Fn stats_blob_tostr , the .Dv SB_STRFMT_FREEFORM .Fa fmt and the .Dv SB_TOSTR_OBJDUMP flag, the rendered output is: .Bd -literal struct statsblobv1@0x8016250a0, abi=1, endian=1, maxsz=136, cursz=136, \\ created=6294158585626144, lastrst=6294158585626144, flags=0x0000, \\ stats_off=56, statsdata_off=112, tplhash=2994056564 vois[0]: id=0, name="", flags=0x0001, dtype=INT_S64, voistatmaxid=3, \\ stats_off=80 vois[0]stat[0]: stype=VOISTATE, flags=0x0000, dtype=VOISTATE, \\ dsz=8, data_off=120 voistatdata: prev=0 vois[0]stat[1]: stype=-1 vois[0]stat[2]: stype=-1 vois[0]stat[3]: stype=MIN, flags=0x0000, dtype=INT_S64, \\ dsz=8, data_off=128 voistatdata: 9223372036854775807 vois[1]: id=-1 vois[2]: id=2, name="", flags=0x0000, dtype=INT_U32, voistatmaxid=2, \\ stats_off=56 vois[2]stat[0]: stype=-1 vois[2]stat[1]: stype=SUM, flags=0x0000, dtype=INT_U32, dsz=4, \\ data_off=112 voistatdata: 0 vois[2]stat[2]: stype=MAX, flags=0x0000, dtype=INT_U32, dsz=4, \\ data_off=116 voistatdata: 0 .Ed .Pp Note: The .Qq \e present in the rendered output above indicates a manual line break inserted to keep the man page within 80 columns and is not part of the actual output. .Ss Locking The .Nm framework does not provide any concurrency protection at the individual blob level, instead requiring that consumers guarantee mutual exclusion when calling API functions that reference a non-template blob. .Pp The list of templates is protected with a .Xr rwlock 9 in-kernel, and .Xr pthread 3 rw lock in user space to support concurrency between template management and blob initialization operations. .Sh RETURN VALUES .Fn stats_tpl_alloc returns a runtime-stable template slot ID on success, or a negative errno on failure. -EINVAL is returned if any problems are detected with the arguments. -EEXIST is returned if an existing template is registered with the same name. -ENOMEM is returned if a required memory allocation fails. .Pp .Fn stats_tpl_fetch_allocid returns a runtime-stable template slot ID, or negative errno on failure. -ESRCH is returned if no registered template matches the specified name and/or hash. .Pp .Fn stats_tpl_fetch returns 0 on success, or ENOENT if an invalid .Fa tpl_id is specified. .Pp .Fn stats_tpl_id2name returns 0 on success, or an errno on failure. EOVERFLOW is returned if the length of .Fa buf specified by .Fa len is too short to hold the template's name. ENOENT is returned if an invalid .Fa tpl_id is specified. .Pp .Fn stats_tpl_sample_rollthedice returns a valid template slot id selected from .Fa rates or -1 if a NULL selection was made, that is no stats collection this roll. .Pp .Fn stats_tpl_add_voistats return 0 on success, or an errno on failure. EINVAL is returned if any problems are detected with the arguments. EFBIG is returned if the resulting blob would have exceeded the maximum size. EOPNOTSUPP is returned if an attempt is made to add more VOI stats to a previously configured VOI. ENOMEM is returned if a required memory allocation fails. .Pp .Fn stats_voi_update_abs_ and .Fn stats_voi_update_rel_ return 0 on success, or EINVAL if any problems are detected with the arguments. .Pp .Fn stats_blob_init returns 0 on success, or an errno on failure. EINVAL is returned if any problems are detected with the arguments. EOVERFLOW is returned if the template blob's .Fa cursz is larger than the .Fa maxsz of the blob being initialized. .Pp .Fn stats_blob_alloc returns a pointer to a newly allocated and initialized blob based on the specified template with slot ID .Fa tpl_id , or NULL if the memory allocation failed. .Pp .Fn stats_blob_clone and .Fn stats_blob_snapshot return 0 on success, or an errno on failure. EINVAL is returned if any problems are detected with the arguments. ENOMEM is returned if the SB_CLONE_ALLOCDST flag was specified and the memory allocation for .Fa dst fails. EOVERFLOW is returned if the src blob's .Fa cursz is larger than the .Fa maxsz of the .Fa dst blob. .Pp .Fn stats_blob_visit returns 0 on success, or EINVAL if any problems are detected with the arguments. .Pp .Fn stats_blob_tostr and .Fn stats_voistatdata_tostr return 0 on success, or an errno on failure. EINVAL is returned if any problems are detected with the arguments, otherwise any error returned by .Fn sbuf_error for .Fa buf is returned. .Pp .Fn stats_voistat_fetch_dptr returns 0 on success, or EINVAL if any problems are detected with the arguments. .Pp .Fn stats_voistat_fetch_ returns 0 on success, or an errno on failure. EINVAL is returned if any problems are detected with the arguments. EFTYPE is returned if the requested data type does not match the blob's data type for the specified .Fa voi_id and .Fa stype . .Sh SEE ALSO .Xr errno 2 , .Xr arb 3 , .Xr qmath 3 , .Xr tcp 4 , .Xr sbuf 9 .Rs .%A "Ted Dunning" .%A "Otmar Ertl" .%T "Computing Extremely Accurate Quantiles Using t-digests" .%U "https://github.com/tdunning/t-digest/raw/master/docs/t-digest-paper/histo.pdf" .Re .Sh HISTORY The .Nm framework first appeared in .Fx 13.0 . .Sh AUTHORS .An -nosplit The .Nm framework and this manual page were written by .An Lawrence Stewart Aq lstewart@FreeBSD.org and sponsored by Netflix, Inc. .Sh CAVEATS Granularity of timing-dependent network statistics, in particular TCP_RTT, depends on the .Dv HZ timer. To minimize the measurement error avoid using HZ lower than 1000.