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author | Lachlan McIlroy <lachlan@redback.melbourne.sgi.com> | 2008-12-29 00:47:18 -0500 |
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committer | Lachlan McIlroy <lachlan@redback.melbourne.sgi.com> | 2008-12-29 00:47:18 -0500 |
commit | 0a8c5395f90f06d128247844b2515c8bf3f2826b (patch) | |
tree | d95382dcdfa303b99d480c01763d6cb6767fdaca /Documentation/tracepoints.txt | |
parent | 25051158bbed127e8672b43396c71c5eb610e5f1 (diff) | |
parent | 3c92ec8ae91ecf59d88c798301833d7cf83f2179 (diff) |
[XFS] Fix merge failures
Merge git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6
Conflicts:
fs/xfs/linux-2.6/xfs_cred.h
fs/xfs/linux-2.6/xfs_globals.h
fs/xfs/linux-2.6/xfs_ioctl.c
fs/xfs/xfs_vnodeops.h
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Diffstat (limited to 'Documentation/tracepoints.txt')
-rw-r--r-- | Documentation/tracepoints.txt | 94 |
1 files changed, 54 insertions, 40 deletions
diff --git a/Documentation/tracepoints.txt b/Documentation/tracepoints.txt index 5d354e167494..6f0a044f5b5e 100644 --- a/Documentation/tracepoints.txt +++ b/Documentation/tracepoints.txt | |||
@@ -3,28 +3,30 @@ | |||
3 | Mathieu Desnoyers | 3 | Mathieu Desnoyers |
4 | 4 | ||
5 | 5 | ||
6 | This document introduces Linux Kernel Tracepoints and their use. It provides | 6 | This document introduces Linux Kernel Tracepoints and their use. It |
7 | examples of how to insert tracepoints in the kernel and connect probe functions | 7 | provides examples of how to insert tracepoints in the kernel and |
8 | to them and provides some examples of probe functions. | 8 | connect probe functions to them and provides some examples of probe |
9 | functions. | ||
9 | 10 | ||
10 | 11 | ||
11 | * Purpose of tracepoints | 12 | * Purpose of tracepoints |
12 | 13 | ||
13 | A tracepoint placed in code provides a hook to call a function (probe) that you | 14 | A tracepoint placed in code provides a hook to call a function (probe) |
14 | can provide at runtime. A tracepoint can be "on" (a probe is connected to it) or | 15 | that you can provide at runtime. A tracepoint can be "on" (a probe is |
15 | "off" (no probe is attached). When a tracepoint is "off" it has no effect, | 16 | connected to it) or "off" (no probe is attached). When a tracepoint is |
16 | except for adding a tiny time penalty (checking a condition for a branch) and | 17 | "off" it has no effect, except for adding a tiny time penalty |
17 | space penalty (adding a few bytes for the function call at the end of the | 18 | (checking a condition for a branch) and space penalty (adding a few |
18 | instrumented function and adds a data structure in a separate section). When a | 19 | bytes for the function call at the end of the instrumented function |
19 | tracepoint is "on", the function you provide is called each time the tracepoint | 20 | and adds a data structure in a separate section). When a tracepoint |
20 | is executed, in the execution context of the caller. When the function provided | 21 | is "on", the function you provide is called each time the tracepoint |
21 | ends its execution, it returns to the caller (continuing from the tracepoint | 22 | is executed, in the execution context of the caller. When the function |
22 | site). | 23 | provided ends its execution, it returns to the caller (continuing from |
24 | the tracepoint site). | ||
23 | 25 | ||
24 | You can put tracepoints at important locations in the code. They are | 26 | You can put tracepoints at important locations in the code. They are |
25 | lightweight hooks that can pass an arbitrary number of parameters, | 27 | lightweight hooks that can pass an arbitrary number of parameters, |
26 | which prototypes are described in a tracepoint declaration placed in a header | 28 | which prototypes are described in a tracepoint declaration placed in a |
27 | file. | 29 | header file. |
28 | 30 | ||
29 | They can be used for tracing and performance accounting. | 31 | They can be used for tracing and performance accounting. |
30 | 32 | ||
@@ -42,14 +44,16 @@ In include/trace/subsys.h : | |||
42 | 44 | ||
43 | #include <linux/tracepoint.h> | 45 | #include <linux/tracepoint.h> |
44 | 46 | ||
45 | DEFINE_TRACE(subsys_eventname, | 47 | DECLARE_TRACE(subsys_eventname, |
46 | TPPTOTO(int firstarg, struct task_struct *p), | 48 | TPPROTO(int firstarg, struct task_struct *p), |
47 | TPARGS(firstarg, p)); | 49 | TPARGS(firstarg, p)); |
48 | 50 | ||
49 | In subsys/file.c (where the tracing statement must be added) : | 51 | In subsys/file.c (where the tracing statement must be added) : |
50 | 52 | ||
51 | #include <trace/subsys.h> | 53 | #include <trace/subsys.h> |
52 | 54 | ||
55 | DEFINE_TRACE(subsys_eventname); | ||
56 | |||
53 | void somefct(void) | 57 | void somefct(void) |
54 | { | 58 | { |
55 | ... | 59 | ... |
@@ -61,31 +65,41 @@ Where : | |||
61 | - subsys_eventname is an identifier unique to your event | 65 | - subsys_eventname is an identifier unique to your event |
62 | - subsys is the name of your subsystem. | 66 | - subsys is the name of your subsystem. |
63 | - eventname is the name of the event to trace. | 67 | - eventname is the name of the event to trace. |
64 | - TPPTOTO(int firstarg, struct task_struct *p) is the prototype of the function | ||
65 | called by this tracepoint. | ||
66 | - TPARGS(firstarg, p) are the parameters names, same as found in the prototype. | ||
67 | 68 | ||
68 | Connecting a function (probe) to a tracepoint is done by providing a probe | 69 | - TPPROTO(int firstarg, struct task_struct *p) is the prototype of the |
69 | (function to call) for the specific tracepoint through | 70 | function called by this tracepoint. |
70 | register_trace_subsys_eventname(). Removing a probe is done through | ||
71 | unregister_trace_subsys_eventname(); it will remove the probe sure there is no | ||
72 | caller left using the probe when it returns. Probe removal is preempt-safe | ||
73 | because preemption is disabled around the probe call. See the "Probe example" | ||
74 | section below for a sample probe module. | ||
75 | |||
76 | The tracepoint mechanism supports inserting multiple instances of the same | ||
77 | tracepoint, but a single definition must be made of a given tracepoint name over | ||
78 | all the kernel to make sure no type conflict will occur. Name mangling of the | ||
79 | tracepoints is done using the prototypes to make sure typing is correct. | ||
80 | Verification of probe type correctness is done at the registration site by the | ||
81 | compiler. Tracepoints can be put in inline functions, inlined static functions, | ||
82 | and unrolled loops as well as regular functions. | ||
83 | |||
84 | The naming scheme "subsys_event" is suggested here as a convention intended | ||
85 | to limit collisions. Tracepoint names are global to the kernel: they are | ||
86 | considered as being the same whether they are in the core kernel image or in | ||
87 | modules. | ||
88 | 71 | ||
72 | - TPARGS(firstarg, p) are the parameters names, same as found in the | ||
73 | prototype. | ||
74 | |||
75 | Connecting a function (probe) to a tracepoint is done by providing a | ||
76 | probe (function to call) for the specific tracepoint through | ||
77 | register_trace_subsys_eventname(). Removing a probe is done through | ||
78 | unregister_trace_subsys_eventname(); it will remove the probe. | ||
79 | |||
80 | tracepoint_synchronize_unregister() must be called before the end of | ||
81 | the module exit function to make sure there is no caller left using | ||
82 | the probe. This, and the fact that preemption is disabled around the | ||
83 | probe call, make sure that probe removal and module unload are safe. | ||
84 | See the "Probe example" section below for a sample probe module. | ||
85 | |||
86 | The tracepoint mechanism supports inserting multiple instances of the | ||
87 | same tracepoint, but a single definition must be made of a given | ||
88 | tracepoint name over all the kernel to make sure no type conflict will | ||
89 | occur. Name mangling of the tracepoints is done using the prototypes | ||
90 | to make sure typing is correct. Verification of probe type correctness | ||
91 | is done at the registration site by the compiler. Tracepoints can be | ||
92 | put in inline functions, inlined static functions, and unrolled loops | ||
93 | as well as regular functions. | ||
94 | |||
95 | The naming scheme "subsys_event" is suggested here as a convention | ||
96 | intended to limit collisions. Tracepoint names are global to the | ||
97 | kernel: they are considered as being the same whether they are in the | ||
98 | core kernel image or in modules. | ||
99 | |||
100 | If the tracepoint has to be used in kernel modules, an | ||
101 | EXPORT_TRACEPOINT_SYMBOL_GPL() or EXPORT_TRACEPOINT_SYMBOL() can be | ||
102 | used to export the defined tracepoints. | ||
89 | 103 | ||
90 | * Probe / tracepoint example | 104 | * Probe / tracepoint example |
91 | 105 | ||