that must be satisfied in order for an actual event to be emitted by
an LTTng tracer when the execution of an application or the Linux kernel
reaches an event source (tracepoint, system call, dynamic probe).
-Event sources can be listed with the linklttng:lttng-list(1) command.
+Event sources can be listed with the man:lttng-list(1) command.
-The linklttng:lttng-disable-event(1) command can be used to disable
+The man:lttng-disable-event(1) command can be used to disable
existing event rules.
Event rules are always assigned to a channel when they are created. If
from the current tracing session.
Events can be enabled while tracing is active
-(use linklttng:lttng-start(1) to make a tracing session active).
+(use man:lttng-start(1) to make a tracing session active).
Event source types
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
(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 <<filter-syntax,Filter expression syntax>> section
+ to true. See the <<filter-expr,Filter expression>> section
below for more information.
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 <<filter-syntax,Filter expression syntax>> section
+ to true. See the <<filter-expr,Filter expression>> 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
currently exist for the chosen tracing session, domain, and channel,
a new event rule is created. Otherwise, the existing event rule is
enabled if it is currently disabled
-(see linklttng:lttng-disable-event(1)).
+(see man:lttng-disable-event(1)).
The option:--all option can be used alongside the option:--tracepoint
or option:--syscall options. When this option is used, no '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.
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
-linklttng: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 linklttng: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 linklttng:lttng-track(1)).
+which is much more efficient (see man:lttng-track(1)).
-Examples:
+Filter expression examples:
----------------------------
msg_id == 23 && size >= 2048
$app.my_provider:my_context == 17.34e9 || some_enum >= 14
---------------------------------------------------------
+---------------------------------------
+$ctx.cpu_id == 2 && filename != "*.log"
+---------------------------------------
+
+------------------------------------------------
+eax_reg & 0xff7 == 0x240 && x[4] >> 12 <= 0x1234
+------------------------------------------------
+
[[log-levels]]
Log levels
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.
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 <<filter-syntax,Filter expression syntax>>
+ event fields. See the <<filter-expr,Filter expression>>
section above for more information.
SEE ALSO
--------
-linklttng:lttng-disable-event(1),
-linklttng:lttng(1)
+man:lttng-disable-event(1),
+man:lttng(1)
projects / lttng-tools.git / blobdiff