[PATCH 15/18] tracing: Add string type for dynamic strings in function based events

Steven Rostedt
2018-02-02T23:10:22Z

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From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Add a "string" type that will create a dynamic length string for the
event, this is the same as the __string() field in normal TRACE_EVENTS.

[ missing 'static' found by Fengguang Wu's kbuild test robot ]
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
Documentation/trace/function-based-events.rst | 19 ++-
kernel/trace/trace_event_ftrace.c | 183 +++++++++++++++++++++++---
2 files changed, 181 insertions(+), 21 deletions(-)

diff --git a/Documentation/trace/function-based-events.rst b/Documentation/trace/function-based-events.rst
index 99ae77cd59e6..6c643ea749e7 100644
--- a/Documentation/trace/function-based-events.rst
+++ b/Documentation/trace/function-based-events.rst
@@ -99,7 +99,7 @@ as follows:
's8' | 's16' | 's32' | 's64' |
'x8' | 'x16' | 'x32' | 'x64' |
'char' | 'short' | 'int' | 'long' | 'size_t' |
- 'symbol'
+ 'symbol' | 'string'

FIELD := <name> | <name> INDEX | <name> OFFSET | <name> OFFSET INDEX

@@ -342,3 +342,20 @@ the format "%s". If a nul is found, the output will stop. Use another type
bash-1470 [003] ...2 980.678715: path_openat->link_path_walk(name=/lib64/ld-linux-x86-64.so.2)
bash-1470 [003] ...2 980.678721: path_openat->link_path_walk(name=ld-2.24.so)
bash-1470 [003] ...2 980.678978: path_lookupat->link_path_walk(name=/etc/ld.so.preload)
+
+
+Dynamic strings
+===============
+
+Static strings are fine, but they can waste a lot of memory in the ring buffer.
+The above allocated 64 bytes for a character array, but most of the output was
+less than 20 characters. Not wanting to truncate strings or waste space on
+the ring buffer, the dynamic string can help.
+
+Use the "string" type for strings that have a large range in size. The max
+size that will be recorded is 512 bytes. If a string is larger than that, then
+it will be truncated.
+
+ # echo 'link_path_walk(string name)' > function_events
+
+Gives the same result as above, but does not waste buffer space.
diff --git a/kernel/trace/trace_event_ftrace.c b/kernel/trace/trace_event_ftrace.c
index dd24b840329d..273c5838a8e2 100644
--- a/kernel/trace/trace_event_ftrace.c
+++ b/kernel/trace/trace_event_ftrace.c
@@ -39,6 +39,7 @@ struct func_event {
struct func_arg *last_arg;
int arg_cnt;
int arg_offset;
+ int has_strings;
};

struct func_file {
@@ -83,6 +84,8 @@ typedef u32 x32;
typedef u16 x16;
typedef u8 x8;
typedef void * symbol;
+/* 2 byte offset, 2 byte length */
+typedef u32 string;

#define TYPE_TUPLE(type) \
{ #type, sizeof(type), is_signed_type(type) }
@@ -105,7 +108,8 @@ typedef void * symbol;
TYPE_TUPLE(u8), \
TYPE_TUPLE(s8), \
TYPE_TUPLE(x8), \
- TYPE_TUPLE(symbol)
+ TYPE_TUPLE(symbol), \
+ TYPE_TUPLE(string)

static struct func_type {
char *name;
@@ -124,6 +128,16 @@ enum {
FUNC_TYPE_MAX
};

+#define MAX_STR 512
+
+/* Two contexts, normal and NMI, hence the " * 2" */
+struct func_string {
+ char buf[MAX_STR * 2];
+};
+
+static struct func_string __percpu *str_buffer;
+static int nr_strings;
+
/**
* arch_get_func_args - retrieve function arguments via pt_regs
* @regs: The registers at the moment the function is called
@@ -163,6 +177,23 @@ int __weak arch_get_func_args(struct pt_regs *regs,
return 0;
}

+static void free_arg(struct func_arg *arg)
+{
+ list_del(&arg->list);
+ if (arg->func_type == FUNC_TYPE_string) {
+ nr_strings--;
+ if (WARN_ON(nr_strings < 0))
+ nr_strings = 0;
+ if (!nr_strings) {
+ free_percpu(str_buffer);
+ str_buffer = NULL;
+ }
+ }
+ kfree(arg->name);
+ kfree(arg->type);
+ kfree(arg);
+}
+
static void free_func_event(struct func_event *func_event)
{
struct func_arg *arg, *n;
@@ -171,10 +202,7 @@ static void free_func_event(struct func_event *func_event)
return;

list_for_each_entry_safe(arg, n, &func_event->args, list) {
- list_del(&arg->list);
- kfree(arg->name);
- kfree(arg->type);
- kfree(arg);
+ free_arg(arg);
}
ftrace_free_filter(&func_event->ops);
kfree(func_event->call.print_fmt);
@@ -255,6 +283,17 @@ static int add_arg(struct func_event *fevent, int ftype, int unsign)
list_add_tail(&arg->list, &fevent->args);
fevent->last_arg = arg;

+ if (ftype == FUNC_TYPE_string) {
+ fevent->has_strings++;
+ nr_strings++;
+ if (nr_strings == 1) {
+ str_buffer = alloc_percpu(struct func_string);
+ if (!str_buffer) {
+ free_arg(arg);
+ return -ENOMEM;
+ }
+ }
+ }
return 0;
}

@@ -344,8 +383,19 @@ process_event(struct func_event *fevent, const char *token, enum func_states sta
return FUNC_STATE_TYPE;

case FUNC_STATE_TYPE:
- if (token[0] == '[')
+ if (token[0] == '[') {
+ /* Strings are already arrays */
+ if (fevent->last_arg->func_type == FUNC_TYPE_string)
+ break;
return FUNC_STATE_ARRAY;
+ }
+ if (fevent->last_arg->func_type == FUNC_TYPE_string) {
+ type = kstrdup("__data_loc char[]", GFP_KERNEL);
+ if (!type)
+ break;
+ kfree(fevent->last_arg->type);
+ fevent->last_arg->type = type;
+ }
/* Fall through */
case FUNC_STATE_ARRAY_END:
if (WARN_ON(!fevent->last_arg))
@@ -473,7 +523,7 @@ process_event(struct func_event *fevent, const char *token, enum func_states sta
return FUNC_STATE_END;
}

-static long long get_arg(struct func_arg *arg, unsigned long val)
+static long long __get_arg(struct func_arg *arg, unsigned long val)
{
char buf[8];
int ret;
@@ -485,8 +535,8 @@ static long long get_arg(struct func_arg *arg, unsigned long val)

val = val + (arg->indirect ^ INDIRECT_FLAG);

- /* Arrays do their own indirect reads */
- if (arg->array)
+ /* Arrays and strings do their own indirect reads */
+ if (arg->array || arg->func_type == FUNC_TYPE_string)
return val;

ret = probe_kernel_read(buf, (void *)val, arg->size);
@@ -510,6 +560,15 @@ static long long get_arg(struct func_arg *arg, unsigned long val)
return val;
}

+static long long get_arg(struct func_arg *arg, long *args)
+{
+ /* Is arg an address and not a parameter? */
+ if (arg->arg < 0)
+ return __get_arg(arg, 0);
+ else
+ return __get_arg(arg, args[arg->arg]);
+}
+
static void get_array(void *dst, struct func_arg *arg, unsigned long val)
{
void *ptr = (void *)val;
@@ -525,6 +584,67 @@ static void get_array(void *dst, struct func_arg *arg, unsigned long val)
}
}

+static int read_string(char *str, unsigned long addr)
+{
+ unsigned long flags;
+ struct func_string *strbuf;
+ char *ptr = (void *)addr;
+ char *buf;
+ int ret;
+
+ if (!str_buffer)
+ return 0;
+
+ strbuf = this_cpu_ptr(str_buffer);
+ buf = &strbuf->buf[0];
+
+ if (in_nmi())
+ buf += MAX_STR;
+
+ local_irq_save(flags);
+ ret = strncpy_from_unsafe(buf, ptr, MAX_STR);
+ if (ret < 0)
+ ret = 0;
+ if (ret > 0 && str)
+ memcpy(str, buf, ret);
+ local_irq_restore(flags);
+
+ return ret;
+}
+
+static int calculate_strings(struct func_event *func_event, int nr_args, long *args)
+{
+ struct func_arg *arg;
+ unsigned long val;
+ int str_count = 0;
+ int size = 0;
+
+ list_for_each_entry(arg, &func_event->args, list) {
+ if (arg->func_type != FUNC_TYPE_string)
+ continue;
+ if (arg->arg < nr_args)
+ val = get_arg(arg, args);
+ else
+ goto skip;
+ size += read_string(NULL, val);
+ skip:
+ if (++str_count >= func_event->has_strings)
+ return size;
+ }
+ return size;
+}
+
+static int get_string(unsigned long addr, unsigned int idx,
+ unsigned int *info, char *data)
+{
+ int len;
+
+ len = read_string(data, addr);
+ *info = len << 16 | idx;
+
+ return len;
+}
+
static void func_event_trace(struct trace_event_file *trace_file,
struct func_event *func_event,
unsigned long ip, unsigned long parent_ip,
@@ -538,6 +658,8 @@ static void func_event_trace(struct trace_event_file *trace_file,
long args[func_event->arg_cnt];
long long val = 1;
unsigned long irq_flags;
+ int str_offset;
+ int str_idx = 0;
int nr_args = 0;
int size;
int pc;
@@ -550,6 +672,12 @@ static void func_event_trace(struct trace_event_file *trace_file,

size = func_event->arg_offset + sizeof(*entry);

+ if (func_event->arg_cnt)
+ nr_args = arch_get_func_args(pt_regs, 0, func_event->arg_cnt, args);
+
+ if (func_event->has_strings)
+ size += calculate_strings(func_event, nr_args, args);
+
event = trace_event_buffer_lock_reserve(&buffer, trace_file,
call->event.type,
size, irq_flags, pc);
@@ -559,21 +687,22 @@ static void func_event_trace(struct trace_event_file *trace_file,
entry = ring_buffer_event_data(event);
entry->ip = ip;
entry->parent_ip = parent_ip;
- if (func_event->arg_cnt)
- nr_args = arch_get_func_args(pt_regs, 0, func_event->arg_cnt, args);

list_for_each_entry(arg, &func_event->args, list) {
- if (arg->arg < nr_args) {
- /* Is arg an address and not a parameter? */
- if (arg->arg < 0)
- val = get_arg(arg, 0);
- else
- val = get_arg(arg, args[arg->arg]);
- } else
+ if (arg->arg < nr_args)
+ val = get_arg(arg, args);
+ else
val = 0;
if (arg->array)
get_array(&entry->data[arg->offset], arg, val);
- else
+ else if (arg->func_type == FUNC_TYPE_string) {
+ str_offset = sizeof(struct func_event_hdr) +
+ func_event->arg_offset;
+
+ str_idx += get_string(val, str_offset + str_idx,
+ (unsigned int *)&entry->data[arg->offset],
+ &entry->data[func_event->arg_offset + str_idx]);
+ } else
memcpy(&entry->data[arg->offset], &val, arg->size);
}

@@ -610,6 +739,11 @@ static void make_fmt(struct func_arg *arg, char *fmt)

fmt[c++] = '%';

+ if (arg->func_type == FUNC_TYPE_string) {
+ fmt[c++] = 's';
+ goto out;
+ }
+
if (arg->func_type == FUNC_TYPE_char) {
if (arg->array)
fmt[c++] = 's';
@@ -667,6 +801,7 @@ func_event_print(struct trace_iterator *iter, int flags,
char fmt[FMT_SIZE];
void *data;
bool comma = false;
+ int info;
int a;

entry = (struct func_event_hdr *)iter->ent;
@@ -692,6 +827,11 @@ func_event_print(struct trace_iterator *iter, int flags,
comma = true;
write_data(s, arg, fmt, data);
}
+ } else if (arg->func_type == FUNC_TYPE_string) {
+ info = *(unsigned int *)data;
+ info = (info & 0xffff) - sizeof(struct func_event_hdr);
+ data = &entry->data[info];
+ trace_seq_printf(s, fmt, data);
} else
write_data(s, arg, fmt, data);
}
@@ -866,7 +1006,10 @@ static int __set_print_fmt(struct func_event *func_event,
len = update_len(len, i);
}
} else {
- i = snprintf(buf + r, len, ", REC->%s", arg->name);
+ if (arg->func_type == FUNC_TYPE_string)
+ i = snprintf(buf + r, len, ", __get_str(%s)", arg->name);
+ else
+ i = snprintf(buf + r, len, ", REC->%s", arg->name);
r += i;
len = update_len(len, i);
}
--
2.15.1