X-Git-Url: https://git.lttng.org/?p=lttng-tools.git;a=blobdiff_plain;f=doc%2Fman%2Flttng-enable-event.1.txt;h=d53feb5d59669de520a786b7faa6aef8acb57d81;hp=afdbd6747e336fe4a42ae14c311d57011aeb7f57;hb=11613178f13a68334d5163e5983fc4ef09911718;hpb=7c1a4458be934fec31aa27a0eb52e4d0b8cb3803 diff --git a/doc/man/lttng-enable-event.1.txt b/doc/man/lttng-enable-event.1.txt index afdbd6747..d53feb5d5 100644 --- a/doc/man/lttng-enable-event.1.txt +++ b/doc/man/lttng-enable-event.1.txt @@ -107,10 +107,10 @@ a _don't care_. For example, consider the following commands: [role="term"] ----------------------------------------------------------------- -lttng enable-event --userspace hello:world -lttng enable-event --userspace hello:world --loglevel=TRACE_INFO ----------------------------------------------------------------- +---- +$ lttng enable-event --userspace hello:world +$ lttng enable-event --userspace hello:world --loglevel=TRACE_INFO +---- Here, two event rules are created. The first one has a single condition: the tracepoint name must match `hello:world`. The second one has two @@ -133,12 +133,13 @@ The available conditions for the Linux kernel domain are: (option:--probe or option:--function option's argument) which must match event source's equivalent. + -Wildcard using the `*` character are supported _at the end_ of -tracepoint and system call names. +You can use `*` characters at any place in the tracepoint or system +call name as wildcards to match zero or more characters. To use a +literal `*` character, use :escwc:. * Filter expression (option:--filter option) executed against the dynamic values of event fields at execution time that must evaluate - to true. See the <> section + to true. See the <> section below for more information. The available conditions for the application domains are: @@ -146,14 +147,15 @@ The available conditions for the application domains are: * Tracepoint name ('EVENT' with option:--tracepoint option) which must match event source's equivalent. + -Wildcard using the `*` character are supported _at the end_ of -tracepoint names. When creating an event rule with a tracepoint name -containing a wildcard, specific tracepoint names can be excluded from -the match using the option:--exclude option. +You can use `*` characters at any place in the tracepoint name as +wildcards to match zero or more characters. To use a literal `*` +character, use :escwc:. When you create an event rule with a tracepoint +name containing a wildcard, you can exclude specific tracepoint names +from the match with the option:--exclude option. * Filter expression (option:--filter option) executed against the dynamic values of event fields at execution time that must evaluate - to true. See the <> section + to true. See the <> section below for more information. * Event's log level that must be at least as severe as a given log level (option:--loglevel option) or match exactly a given log @@ -173,10 +175,10 @@ chosen channel and tracing session. It is the equivalent of an 'EVENT' argument named `*` (wildcard). -[[filter-syntax]] -Filter expression syntax -~~~~~~~~~~~~~~~~~~~~~~~~ -Filter expressions can be specified with the option:--filter option +[[filter-expr]] +Filter expression +~~~~~~~~~~~~~~~~~ +A filter expression can be specified with the option:--filter option when creating a new event rule. If the filter expression evaluates to true when executed against the dynamic values of an event's fields when tracing, the filtering condition passes. @@ -185,66 +187,125 @@ NOTE: Make sure to **single-quote** the filter expression when running the command from a shell, as filter expressions typically include characters having a special meaning for most shells. -The filter expression syntax is very similar to C language conditional -expressions (expressions that can be evaluated by an `if` statement). - -The following logical operators are supported: - -[width="40%",options="header"] -|===================================== -| Name | Syntax -| Logical negation (NOT) | `!a` -| Logical conjunction (AND) | `a && b` -| Logical disjunction (OR) | `a \|\| b` -|===================================== - -The following comparison operators/relational operators are supported: +The filter expression syntax is similar to C language conditional +expressions (expressions that can be evaluated by an `if` statement), +albeit with a few differences: -[width="40%",options="header"] -|==================================== -| Name | Syntax -| Equal to | `a == b` -| Not equal to | `a != b` -| Greater than | `a > b` -| Less than | `a < b` -| Greater than or equal to | `a >= b` -| Less than or equal to | `a <= b` -|==================================== - -The arithmetic and bitwise operators are :not: supported. - -The precedence table of the operators above is the same as the one of -the C language. Parentheses are supported to bypass this. +* C integer and floating point number constants are supported, as well + as literal strings between double quotes (`"`). You can use `*` + characters at any place in a literal string as wildcards to match zero + or more characters. To use a literal `*` character, use :escwc:. ++ +Examples: `32`, `-0x17`, `0755`, `12.34`, ++"a :escbs:"literal string:escbs:""+, `"src/*/*.h"`. -The dynamic value of an event field is read by using its name as -a C identifier. +* The dynamic value of an event field is read by using its name as a C + identifier. ++ +The dot and square bracket notations are available, like in the C +language, to access nested structure and array/sequence fields. +Only a constant, positive integer number can be used within square +brackets. If the index is out of bounds, the whole filter expression +evaluates to false (the event is discarded). ++ +An enumeration field's value is an integer. ++ +When the expression's field does not exist, the whole filter expression +evaluates to false. ++ +Examples: `my_field`, `target_cpu`, `seq[7]`, `msg.user[1].data[2][17]`. -The dynamic value of a statically-known context field is read by -prefixing its name with `$ctx.`. Statically-known context fields are -context fields added to channels without the `$app.` prefix using the -man:lttng-add-context(1) command. +* The dynamic value of a statically-known context field is read by + prefixing its name with `$ctx.`. Statically-known context fields are + context fields added to channels without the `$app.` prefix using the + man:lttng-add-context(1) command. ++ +When the expression's statically-known context field does not exist, +the whole filter expression evaluates to false. ++ +Examples: `$ctx.prio`, `$ctx.preemptible`, +`$ctx.perf:cpu:stalled-cycles-frontend`. -The dynamic value of an application-specific context field is read by -prefixing its name with `$app.` (follows the format used to add such a -context field with the man:lttng-add-context(1) command). +* The dynamic value of an application-specific context field is read by + prefixing its name with `$app.` (follows the format used to add such a + context field with the man:lttng-add-context(1) command). ++ +When the expression's application-specific context field does not exist, +the whole filter expression evaluates to false. ++ +Example: `$app.server:cur_user`. + +The following precedence table shows the operators which are supported +in a filter expression. In this table, the highest precedence is 1. +Parentheses are supported to bypass the default order. + +IMPORTANT: Unlike the C language, the `lttng enable-event` filter +expression syntax's bitwise AND and OR operators (`&` and `|`) take +precedence over relational operators (`<`, `<=`, `>`, `>=`, `==`, and +`!=`). This means the filter expression `2 & 2 == 2` is true while the +equivalent C expression is false. + +[options="header"] +|=== +|Precedence |Operator |Description |Associativity +|1 |`-` |Unary minus |Right-to-left +|1 |`+` |Unary plus |Right-to-left +|1 |`!` |Logical NOT |Right-to-left +|1 |`~` |Bitwise NOT |Right-to-left +|2 |`<<` |Bitwise left shift |Left-to-right +|2 |`>>` |Bitwise right shift |Left-to-right +|3 |`&` |Bitwise AND |Left-to-right +|4 |`^` |Bitwise XOR |Left-to-right +|5 |`\|` |Bitwise OR |Left-to-right +|6 |`<` |Less than |Left-to-right +|6 |`<=` |Less than or equal to |Left-to-right +|6 |`>` |Greater than |Left-to-right +|6 |`>=` |Greater than or equal to |Left-to-right +|7 |`==` |Equal to |Left-to-right +|7 |`!=` |Not equal to |Left-to-right +|8 |`&&` |Logical AND |Left-to-right +|9 |`\|\|` |Logical OR |Left-to-right +|=== + +The arithmetic operators are :not: supported. + +All integer constants and fields are first casted to signed 64-bit +integers. The representation of negative integers is two's complement. +This means that, for example, the signed 8-bit integer field 0xff (-1) +becomes 0xffffffffffffffff (still -1) once casted. + +Before a bitwise operator is applied, all its operands are casted to +unsigned 64-bit integers, and the result is casted back to a signed +64-bit integer. For the bitwise NOT operator, it is the equivalent of +this C expression: + +[source,c] +---- +(int64_t) ~((uint64_t) val) +---- -When a comparison includes a non existent event field, the whole filter -expression evaluates to false (the event is discarded). +For the binary bitwise operators, it is the equivalent of those C +expressions: -C integer and floating point number constants are supported, as well as -literal strings between double quotes (`"`). Literal strings can contain -a wildcard character (`*`) at the end to match more than one string. -This wildcard can be escaped using :escwc:. +[source,c] +---- +(int64_t) ((uint64_t) lhs >> (uint64_t) rhs) +(int64_t) ((uint64_t) lhs << (uint64_t) rhs) +(int64_t) ((uint64_t) lhs & (uint64_t) rhs) +(int64_t) ((uint64_t) lhs ^ (uint64_t) rhs) +(int64_t) ((uint64_t) lhs | (uint64_t) rhs) +---- -LTTng-UST enumeration fields can be compared to integer values (fields -or constants). +If the right-hand side of a bitwise shift operator (`<<` and `>>`) is +not in the [0,{nbsp}63] range, the whole filter expression evaluates to +false. NOTE: Although it is possible to filter the process ID of an event when the `pid` context has been added to its channel using, for example, `$ctx.pid == 2832`, it is recommended to use the PID tracker instead, which is much more efficient (see man:lttng-track(1)). -Examples: +Filter expression examples: ---------------------------- msg_id == 23 && size >= 2048 @@ -258,6 +319,14 @@ $ctx.procname == "lttng*" && (!flag || poel < 34) $app.my_provider:my_context == 17.34e9 || some_enum >= 14 --------------------------------------------------------- +--------------------------------------- +$ctx.cpu_id == 2 && filename != "*.log" +--------------------------------------- + +------------------------------------------------ +eax_reg & 0xff7 == 0x240 && x[4] >> 12 <= 0x1234 +------------------------------------------------ + [[log-levels]] Log levels @@ -353,11 +422,11 @@ option:-u, option:--userspace:: Target ~~~~~~ -option:-c, option:--channel='CHANNEL':: +option:-c 'CHANNEL', option:--channel='CHANNEL':: Create or enable event rules in the channel named 'CHANNEL' instead of the default channel name `channel0`. -option:-s, option:--session='SESSION':: +option:-s 'SESSION', option:--session='SESSION':: Create or enable event rules in the tracing session named 'SESSION' instead of the current tracing session. @@ -409,16 +478,18 @@ option:--loglevel-only='LOGLEVEL':: Filtering and exclusion ~~~~~~~~~~~~~~~~~~~~~~~ -option:-x, option:--exclude='EVENT'[,'EVENT']...:: +option:-x 'EVENT'[,'EVENT']..., option:--exclude='EVENT'[,'EVENT']...:: Exclude events named 'EVENT' from the event rule. This option - can be used when the command's 'EVENT' argument contains a wildcard - (`*`) to exclude specific names. Only available with application - domains. + can be used when the command's 'EVENT' argument contains at least + one wildcard star (`*`) to exclude specific names. 'EVENT' can also + contain wildcard stars. To use a + literal `,` character, use :esccomma:. + Only available with the option:--userspace domain. -option:-f, option:--filter='EXPR':: +option:-f 'EXPR', option:--filter='EXPR':: Add filter expression condition to the event rule. Expression 'EXPR' must evaluate to true when executed against the dynamic values of - event fields. See the <> + event fields. See the <> section above for more information.