LinuxLists.cc - [PATCH v4 0/4] tracing/user_events: Introduce multi-format events

2024-02-22 00:18:34

Subject: [PATCH v4 0/4] tracing/user_events: Introduce multi-format events

2024-02-22 00:18:48

Subject: [PATCH v4 2/4] tracing/user_events: Introduce multi-format events

Currently user_events supports 1 event with the same name and must have
the exact same format when referenced by multiple programs. This opens
an opportunity for malicous or poorly thought through programs to
create events that others use with different formats. Another scenario
is user programs wishing to use the same event name but add more fields
later when the software updates. Various versions of a program may be
running side-by-side, which is prevented by the current single format
requirement.

Add a new register flag (USER_EVENT_REG_MULTI_FORMAT) which indicates
the user program wishes to use the same user_event name, but may have
several different formats of the event. When this flag is used, create
the underlying tracepoint backing the user_event with a unique name
per-version of the format. It's important that existing ABI users do
not get this logic automatically, even if one of the multi format
events matches the format. This ensures existing programs that create
events and assume the tracepoint name will match exactly continue to
work as expected. Add logic to only check multi-format events with
other multi-format events and single-format events to only check
single-format events during find.

Change system name of the multi-format event tracepoint to ensure that
multi-format events are isolated completely from single-format events.
This prevents single-format names from conflicting with multi-format
events if they end with the same suffix as the multi-format events.

Add a register_name (reg_name) to the user_event struct which allows for
split naming of events. We now have the name that was used to register
within user_events as well as the unique name for the tracepoint. Upon
registering events ensure matches based on first the reg_name, followed
by the fields and format of the event. This allows for multiple events
with the same registered name to have different formats. The underlying
tracepoint will have a unique name in the format of {reg_name}.{unique_id}.

For example, if both "test u32 value" and "test u64 value" are used with
the USER_EVENT_REG_MULTI_FORMAT the system would have 2 unique
tracepoints. The dynamic_events file would then show the following:
u:test u64 count
u:test u32 count

The actual tracepoint names look like this:
test.0
test.1

Both would be under the new user_events_multi system name to prevent the
older ABI from being used to squat on multi-formatted events and block
their use.

Deleting events via "!u:test u64 count" would only delete the first
tracepoint that matched that format. When the delete ABI is used all
events with the same name will be attempted to be deleted. If
per-version deletion is required, user programs should either not use
persistent events or delete them via dynamic_events.

Signed-off-by: Beau Belgrave <[email protected]>
---
include/uapi/linux/user_events.h | 6 +-
kernel/trace/trace_events_user.c | 102 +++++++++++++++++++++++++++----
2 files changed, 95 insertions(+), 13 deletions(-)

diff --git a/include/uapi/linux/user_events.h b/include/uapi/linux/user_events.h
index f74f3aedd49c..a03de03dccbc 100644
--- a/include/uapi/linux/user_events.h
+++ b/include/uapi/linux/user_events.h
@@ -12,6 +12,7 @@
#include <linux/ioctl.h>

#define USER_EVENTS_SYSTEM "user_events"
+#define USER_EVENTS_MULTI_SYSTEM "user_events_multi"
#define USER_EVENTS_PREFIX "u:"

/* Create dynamic location entry within a 32-bit value */
@@ -22,8 +23,11 @@ enum user_reg_flag {
/* Event will not delete upon last reference closing */
USER_EVENT_REG_PERSIST = 1U << 0,

+ /* Event will be allowed to have multiple formats */
+ USER_EVENT_REG_MULTI_FORMAT = 1U << 1,
+
/* This value or above is currently non-ABI */
- USER_EVENT_REG_MAX = 1U << 1,
+ USER_EVENT_REG_MAX = 1U << 2,
};

/*
diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index dda58681247e..044920c415e7 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -34,7 +34,8 @@

/* Limit how long of an event name plus args within the subsystem. */
#define MAX_EVENT_DESC 512
-#define EVENT_NAME(user_event) ((user_event)->tracepoint.name)
+#define EVENT_NAME(user_event) ((user_event)->reg_name)
+#define EVENT_TP_NAME(user_event) ((user_event)->tracepoint.name)
#define MAX_FIELD_ARRAY_SIZE 1024

/*
@@ -54,10 +55,13 @@
* allows isolation for events by various means.
*/
struct user_event_group {
- char *system_name;
- struct hlist_node node;
- struct mutex reg_mutex;
+ char *system_name;
+ char *system_multi_name;
+ struct hlist_node node;
+ struct mutex reg_mutex;
DECLARE_HASHTABLE(register_table, 8);
+ /* ID that moves forward within the group for multi-event names */
+ u64 multi_id;
};

/* Group for init_user_ns mapping, top-most group */
@@ -78,6 +82,7 @@ static unsigned int current_user_events;
*/
struct user_event {
struct user_event_group *group;
+ char *reg_name;
struct tracepoint tracepoint;
struct trace_event_call call;
struct trace_event_class class;
@@ -127,6 +132,8 @@ struct user_event_enabler {

#define ENABLE_BIT(e) ((int)((e)->values & ENABLE_VAL_BIT_MASK))

+#define EVENT_MULTI_FORMAT(f) ((f) & USER_EVENT_REG_MULTI_FORMAT)
+
/* Used for asynchronous faulting in of pages */
struct user_event_enabler_fault {
struct work_struct work;
@@ -330,6 +337,7 @@ static void user_event_put(struct user_event *user, bool locked)
static void user_event_group_destroy(struct user_event_group *group)
{
kfree(group->system_name);
+ kfree(group->system_multi_name);
kfree(group);
}

@@ -348,6 +356,11 @@ static char *user_event_group_system_name(void)
return system_name;
}

+static char *user_event_group_system_multi_name(void)
+{
+ return kstrdup(USER_EVENTS_MULTI_SYSTEM, GFP_KERNEL);
+}
+
static struct user_event_group *current_user_event_group(void)
{
return init_group;
@@ -367,6 +380,11 @@ static struct user_event_group *user_event_group_create(void)
if (!group->system_name)
goto error;

+ group->system_multi_name = user_event_group_system_multi_name();
+
+ if (!group->system_multi_name)
+ goto error;
+
mutex_init(&group->reg_mutex);
hash_init(group->register_table);

@@ -1482,6 +1500,11 @@ static int destroy_user_event(struct user_event *user)
hash_del(&user->node);

user_event_destroy_validators(user);
+
+ /* If we have different names, both must be freed */
+ if (EVENT_NAME(user) != EVENT_TP_NAME(user))
+ kfree(EVENT_TP_NAME(user));
+
kfree(user->call.print_fmt);
kfree(EVENT_NAME(user));
kfree(user);
@@ -1504,12 +1527,24 @@ static struct user_event *find_user_event(struct user_event_group *group,
*outkey = key;

hash_for_each_possible(group->register_table, user, node, key) {
+ /*
+ * Single-format events shouldn't return multi-format
+ * events. Callers expect the underlying tracepoint to match
+ * the name exactly in these cases. Only check like-formats.
+ */
+ if (EVENT_MULTI_FORMAT(flags) != EVENT_MULTI_FORMAT(user->reg_flags))
+ continue;
+
if (strcmp(EVENT_NAME(user), name))
continue;

if (user_fields_match(user, argc, argv))
return user_event_get(user);

+ /* Scan others if this is a multi-format event */
+ if (EVENT_MULTI_FORMAT(flags))
+ continue;
+
return ERR_PTR(-EADDRINUSE);
}

@@ -1889,8 +1924,12 @@ static bool user_event_match(const char *system, const char *event,
struct user_event *user = container_of(ev, struct user_event, devent);
bool match;

- match = strcmp(EVENT_NAME(user), event) == 0 &&
- (!system || strcmp(system, USER_EVENTS_SYSTEM) == 0);
+ match = strcmp(EVENT_NAME(user), event) == 0;
+
+ if (match && system) {
+ match = strcmp(system, user->group->system_name) == 0 ||
+ strcmp(system, user->group->system_multi_name) == 0;
+ }

if (match)
match = user_fields_match(user, argc, argv);
@@ -1923,6 +1962,33 @@ static int user_event_trace_register(struct user_event *user)
return ret;
}

+static int user_event_set_tp_name(struct user_event *user)
+{
+ lockdep_assert_held(&user->group->reg_mutex);
+
+ if (EVENT_MULTI_FORMAT(user->reg_flags)) {
+ char *multi_name;
+
+ multi_name = kasprintf(GFP_KERNEL_ACCOUNT, "%s.%llx",
+ user->reg_name, user->group->multi_id);
+
+ if (!multi_name)
+ return -ENOMEM;
+
+ user->call.name = multi_name;
+ user->tracepoint.name = multi_name;
+
+ /* Inc to ensure unique multi-event name next time */
+ user->group->multi_id++;
+ } else {
+ /* Non Multi-format uses register name */
+ user->call.name = user->reg_name;
+ user->tracepoint.name = user->reg_name;
+ }
+
+ return 0;
+}
+
/*
* Parses the event name, arguments and flags then registers if successful.
* The name buffer lifetime is owned by this method for success cases only.
@@ -1985,7 +2051,13 @@ static int user_event_parse(struct user_event_group *group, char *name,
INIT_LIST_HEAD(&user->validators);

user->group = group;
- user->tracepoint.name = name;
+ user->reg_name = name;
+ user->reg_flags = reg_flags;
+
+ ret = user_event_set_tp_name(user);
+
+ if (ret)
+ goto put_user;

ret = user_event_parse_fields(user, args);

@@ -1999,11 +2071,14 @@ static int user_event_parse(struct user_event_group *group, char *name,

user->call.data = user;
user->call.class = &user->class;
- user->call.name = name;
user->call.flags = TRACE_EVENT_FL_TRACEPOINT;
user->call.tp = &user->tracepoint;
user->call.event.funcs = &user_event_funcs;
- user->class.system = group->system_name;
+
+ if (EVENT_MULTI_FORMAT(user->reg_flags))
+ user->class.system = group->system_multi_name;
+ else
+ user->class.system = group->system_name;

user->class.fields_array = user_event_fields_array;
user->class.get_fields = user_event_get_fields;
@@ -2025,8 +2100,6 @@ static int user_event_parse(struct user_event_group *group, char *name,
if (ret)
goto put_user_lock;

- user->reg_flags = reg_flags;
-
if (user->reg_flags & USER_EVENT_REG_PERSIST) {
/* Ensure we track self ref and caller ref (2) */
refcount_set(&user->refcnt, 2);
@@ -2050,6 +2123,11 @@ static int user_event_parse(struct user_event_group *group, char *name,
user_event_destroy_fields(user);
user_event_destroy_validators(user);
kfree(user->call.print_fmt);
+
+ /* Caller frees reg_name on error, but not multi-name */
+ if (EVENT_NAME(user) != EVENT_TP_NAME(user))
+ kfree(EVENT_TP_NAME(user));
+
kfree(user);
return ret;
}
@@ -2641,7 +2719,7 @@ static int user_seq_show(struct seq_file *m, void *p)
hash_for_each(group->register_table, i, user, node) {
status = user->status;

- seq_printf(m, "%s", EVENT_NAME(user));
+ seq_printf(m, "%s", EVENT_TP_NAME(user));

if (status != 0)
seq_puts(m, " #");
--
2.34.1

2024-02-22 00:19:01

by Beau Belgrave

[permalink] [raw]

Subject: [PATCH v4 1/4] tracing/user_events: Prepare find/delete for same name events

The current code for finding and deleting events assumes that there will
never be cases when user_events are registered with the same name, but
different formats. Scenarios exist where programs want to use the same
name but have different formats. An example is multiple versions of a
program running side-by-side using the same event name, but with updated
formats in each version.

This change does not yet allow for multi-format events. If user_events
are registered with the same name but different arguments the programs
see the same return values as before. This change simply makes it
possible to easily accomodate for this.

Update find_user_event() to take in argument parameters and register
flags to accomodate future multi-format event scenarios. Have find
validate argument matching and return error pointers to cover when
an existing event has the same name but different format. Update
callers to handle error pointer logic.

Move delete_user_event() to use hash walking directly now that
find_user_event() has changed. Delete all events found that match the
register name, stop if an error occurs and report back to the user.

Update user_fields_match() to cover list_empty() scenarios now that
find_user_event() uses it directly. This makes the logic consistent
accross several callsites.

Signed-off-by: Beau Belgrave <[email protected]>
---
kernel/trace/trace_events_user.c | 107 +++++++++++++++++--------------
1 file changed, 59 insertions(+), 48 deletions(-)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 9365ce407426..dda58681247e 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -202,6 +202,8 @@ static struct user_event_mm *user_event_mm_get(struct user_event_mm *mm);
static struct user_event_mm *user_event_mm_get_all(struct user_event *user);
static void user_event_mm_put(struct user_event_mm *mm);
static int destroy_user_event(struct user_event *user);
+static bool user_fields_match(struct user_event *user, int argc,
+ const char **argv);

static u32 user_event_key(char *name)
{
@@ -1493,17 +1495,24 @@ static int destroy_user_event(struct user_event *user)
}

static struct user_event *find_user_event(struct user_event_group *group,
- char *name, u32 *outkey)
+ char *name, int argc, const char **argv,
+ u32 flags, u32 *outkey)
{
struct user_event *user;
u32 key = user_event_key(name);

*outkey = key;

- hash_for_each_possible(group->register_table, user, node, key)
- if (!strcmp(EVENT_NAME(user), name))
+ hash_for_each_possible(group->register_table, user, node, key) {
+ if (strcmp(EVENT_NAME(user), name))
+ continue;
+
+ if (user_fields_match(user, argc, argv))
return user_event_get(user);

+ return ERR_PTR(-EADDRINUSE);
+ }
+
return NULL;
}

@@ -1860,6 +1869,9 @@ static bool user_fields_match(struct user_event *user, int argc,
struct list_head *head = &user->fields;
int i = 0;

+ if (argc == 0)
+ return list_empty(head);
+
list_for_each_entry_reverse(field, head, link) {
if (!user_field_match(field, argc, argv, &i))
return false;
@@ -1880,10 +1892,8 @@ static bool user_event_match(const char *system, const char *event,
match = strcmp(EVENT_NAME(user), event) == 0 &&
(!system || strcmp(system, USER_EVENTS_SYSTEM) == 0);

- if (match && argc > 0)
+ if (match)
match = user_fields_match(user, argc, argv);
- else if (match && argc == 0)
- match = list_empty(&user->fields);

return match;
}
@@ -1922,11 +1932,11 @@ static int user_event_parse(struct user_event_group *group, char *name,
char *args, char *flags,
struct user_event **newuser, int reg_flags)
{
- int ret;
- u32 key;
struct user_event *user;
+ char **argv = NULL;
int argc = 0;
- char **argv;
+ int ret;
+ u32 key;

/* Currently don't support any text based flags */
if (flags != NULL)
@@ -1935,41 +1945,34 @@ static int user_event_parse(struct user_event_group *group, char *name,
if (!user_event_capable(reg_flags))
return -EPERM;

+ if (args) {
+ argv = argv_split(GFP_KERNEL, args, &argc);
+
+ if (!argv)
+ return -ENOMEM;
+ }
+
/* Prevent dyn_event from racing */
mutex_lock(&event_mutex);
- user = find_user_event(group, name, &key);
+ user = find_user_event(group, name, argc, (const char **)argv,
+ reg_flags, &key);
mutex_unlock(&event_mutex);

- if (user) {
- if (args) {
- argv = argv_split(GFP_KERNEL, args, &argc);
- if (!argv) {
- ret = -ENOMEM;
- goto error;
- }
+ if (argv)
+ argv_free(argv);

- ret = user_fields_match(user, argc, (const char **)argv);
- argv_free(argv);
-
- } else
- ret = list_empty(&user->fields);
-
- if (ret) {
- *newuser = user;
- /*
- * Name is allocated by caller, free it since it already exists.
- * Caller only worries about failure cases for freeing.
- */
- kfree(name);
- } else {
- ret = -EADDRINUSE;
- goto error;
- }
+ if (IS_ERR(user))
+ return PTR_ERR(user);
+
+ if (user) {
+ *newuser = user;
+ /*
+ * Name is allocated by caller, free it since it already exists.
+ * Caller only worries about failure cases for freeing.
+ */
+ kfree(name);

return 0;
-error:
- user_event_put(user, false);
- return ret;
}

user = kzalloc(sizeof(*user), GFP_KERNEL_ACCOUNT);
@@ -2052,25 +2055,33 @@ static int user_event_parse(struct user_event_group *group, char *name,
}

/*
- * Deletes a previously created event if it is no longer being used.
+ * Deletes previously created events if they are no longer being used.
*/
static int delete_user_event(struct user_event_group *group, char *name)
{
- u32 key;
- struct user_event *user = find_user_event(group, name, &key);
+ struct user_event *user;
+ struct hlist_node *tmp;
+ u32 key = user_event_key(name);
+ int ret = -ENOENT;

- if (!user)
- return -ENOENT;
+ /* Attempt to delete all event(s) with the name passed in */
+ hash_for_each_possible_safe(group->register_table, user, tmp, node, key) {
+ if (strcmp(EVENT_NAME(user), name))
+ continue;

- user_event_put(user, true);
+ if (!user_event_last_ref(user))
+ return -EBUSY;

- if (!user_event_last_ref(user))
- return -EBUSY;
+ if (!user_event_capable(user->reg_flags))
+ return -EPERM;

- if (!user_event_capable(user->reg_flags))
- return -EPERM;
+ ret = destroy_user_event(user);

- return destroy_user_event(user);
+ if (ret)
+ goto out;
+ }
+out:
+ return ret;
}

/*
--
2.34.1

2024-02-22 00:19:15

by Beau Belgrave

[permalink] [raw]

Subject: [PATCH v4 4/4] tracing/user_events: Document multi-format flag

User programs can now ask user_events to handle the synchronization of
multiple different formats for an event with the same name via the new
USER_EVENT_REG_MULTI_FORMAT flag.

Add a section for USER_EVENT_REG_MULTI_FORMAT that explains the intended
purpose and caveats of using it. Explain how deletion works in these
cases and how to use /sys/kernel/tracing/dynamic_events for per-version
deletion.

Signed-off-by: Beau Belgrave <[email protected]>
---
Documentation/trace/user_events.rst | 27 ++++++++++++++++++++++++++-
1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/Documentation/trace/user_events.rst b/Documentation/trace/user_events.rst
index d8f12442aaa6..1d5a7626e6a6 100644
--- a/Documentation/trace/user_events.rst
+++ b/Documentation/trace/user_events.rst
@@ -92,6 +92,24 @@ The following flags are currently supported.
process closes or unregisters the event. Requires CAP_PERFMON otherwise
-EPERM is returned.

++ USER_EVENT_REG_MULTI_FORMAT: The event can contain multiple formats. This
+ allows programs to prevent themselves from being blocked when their event
+ format changes and they wish to use the same name. When this flag is used the
+ tracepoint name will be in the new format of "name.unique_id" vs the older
+ format of "name". A tracepoint will be created for each unique pair of name
+ and format. This means if several processes use the same name and format,
+ they will use the same tracepoint. If yet another process uses the same name,
+ but a different format than the other processes, it will use a different
+ tracepoint with a new unique id. Recording programs need to scan tracefs for
+ the various different formats of the event name they are interested in
+ recording. The system name of the tracepoint will also use "user_events_multi"
+ instead of "user_events". This prevents single-format event names conflicting
+ with any multi-format event names within tracefs. The unique_id is output as
+ a hex string. Recording programs should ensure the tracepoint name starts with
+ the event name they registered and has a suffix that starts with . and only
+ has hex characters. For example to find all versions of the event "test" you
+ can use the regex "^test\.[0-9a-fA-F]+$".
+
Upon successful registration the following is set.

+ write_index: The index to use for this file descriptor that represents this
@@ -106,6 +124,9 @@ or perf record -e user_events:[name] when attaching/recording.
**NOTE:** The event subsystem name by default is "user_events". Callers should
not assume it will always be "user_events". Operators reserve the right in the
future to change the subsystem name per-process to accommodate event isolation.
+In addition if the USER_EVENT_REG_MULTI_FORMAT flag is used the tracepoint name
+will have a unique id appended to it and the system name will be
+"user_events_multi" as described above.

Command Format
^^^^^^^^^^^^^^
@@ -156,7 +177,11 @@ to request deletes than the one used for registration due to this.
to the event. If programs do not want auto-delete, they must use the
USER_EVENT_REG_PERSIST flag when registering the event. Once that flag is used
the event exists until DIAG_IOCSDEL is invoked. Both register and delete of an
-event that persists requires CAP_PERFMON, otherwise -EPERM is returned.
+event that persists requires CAP_PERFMON, otherwise -EPERM is returned. When
+there are multiple formats of the same event name, all events with the same
+name will be attempted to be deleted. If only a specific version is wanted to
+be deleted then the /sys/kernel/tracing/dynamic_events file should be used for
+that specific format of the event.

Unregistering
-------------
--
2.34.1

2024-02-22 22:06:56

by Steven Rostedt

[permalink] [raw]

Subject: Re: [PATCH v4 1/4] tracing/user_events: Prepare find/delete for same name events

On Thu, 22 Feb 2024 00:18:04 +0000
Beau Belgrave <[email protected]> wrote:

> The current code for finding and deleting events assumes that there will
> never be cases when user_events are registered with the same name, but
> different formats. Scenarios exist where programs want to use the same
> name but have different formats. An example is multiple versions of a
> program running side-by-side using the same event name, but with updated
> formats in each version.
>
> This change does not yet allow for multi-format events. If user_events
> are registered with the same name but different arguments the programs
> see the same return values as before. This change simply makes it
> possible to easily accomodate for this.

accommodate? ;-)

>
> Update find_user_event() to take in argument parameters and register
> flags to accomodate future multi-format event scenarios. Have find

accommodate

> validate argument matching and return error pointers to cover when
> an existing event has the same name but different format. Update
> callers to handle error pointer logic.
>
> Move delete_user_event() to use hash walking directly now that
> find_user_event() has changed. Delete all events found that match the
> register name, stop if an error occurs and report back to the user.
>
> Update user_fields_match() to cover list_empty() scenarios now that
> find_user_event() uses it directly. This makes the logic consistent
> accross several callsites.

across ?

I'll update this.

-- Steve

>
> Signed-off-by: Beau Belgrave <[email protected]>

2024-02-22 22:12:02

by Steven Rostedt

[permalink] [raw]

Subject: Re: [PATCH v4 2/4] tracing/user_events: Introduce multi-format events

On Thu, 22 Feb 2024 00:18:05 +0000
Beau Belgrave <[email protected]> wrote:

> Currently user_events supports 1 event with the same name and must have
> the exact same format when referenced by multiple programs. This opens
> an opportunity for malicous or poorly thought through programs to

malicious? ;-)

-- Steve

> create events that others use with different formats. Another scenario
> is user programs wishing to use the same event name but add more fields
> later when the software updates. Various versions of a program may be
> running side-by-side, which is prevented by the current single format
> requirement.
>
> Add a new register flag (USER_EVENT_REG_MULTI_FORMAT) which indicates
> the user program wishes to use the same user_event name, but may have
> several different formats of the event. When this flag is used, create
> the underlying tracepoint backing the user_event with a unique name
> per-version of the format. It's important that existing ABI users do
> not get this logic automatically, even if one of the multi format
> events matches the format. This ensures existing programs that create
> events and assume the tracepoint name will match exactly continue to
> work as expected. Add logic to only check multi-format events with
> other multi-format events and single-format events to only check
> single-format events during find.
>
> Change system name of the multi-format event tracepoint to ensure that
> multi-format events are isolated completely from single-format events.
> This prevents single-format names from conflicting with multi-format
> events if they end with the same suffix as the multi-format events.
>
> Add a register_name (reg_name) to the user_event struct which allows for
> split naming of events. We now have the name that was used to register
> within user_events as well as the unique name for the tracepoint. Upon
> registering events ensure matches based on first the reg_name, followed
> by the fields and format of the event. This allows for multiple events
> with the same registered name to have different formats. The underlying
> tracepoint will have a unique name in the format of {reg_name}.{unique_id}.
>
> For example, if both "test u32 value" and "test u64 value" are used with
> the USER_EVENT_REG_MULTI_FORMAT the system would have 2 unique
> tracepoints. The dynamic_events file would then show the following:
> u:test u64 count
> u:test u32 count
>
> The actual tracepoint names look like this:
> test.0
> test.1
>
> Both would be under the new user_events_multi system name to prevent the
> older ABI from being used to squat on multi-formatted events and block
> their use.
>
> Deleting events via "!u:test u64 count" would only delete the first
> tracepoint that matched that format. When the delete ABI is used all
> events with the same name will be attempted to be deleted. If
> per-version deletion is required, user programs should either not use
> persistent events or delete them via dynamic_events.
>
> Signed-off-by: Beau Belgrave <[email protected]>