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Subject[PATCH 2/2] tracing/events: Convert format output to seq_file
From: Steven Rostedt <srostedt@redhat.com>

Two new events were added that broke the current format output.

Both from the SCSI system: scsi_dispatch_cmd_done and scsi_dispatch_cmd_timeout

The reason is that their print_fmt exceeded a page size. Since the output
of the format used simple_read_from_buffer and trace_seq, it was limited
to a page size in output.

This patch converts the printing of the format of an event into seq_file,
which allows greater than a page size to be shown.

I diffed all event formats comparing the output with and without this
patch. All matched except for the above two, which showed just:

FORMAT TOO BIG

without this patch, but now properly displays the output with this patch.

v2: Remove updating *pos in seq start function.
[ Thanks to Li Zefan for pointing that out ]

Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Kei Tokunaga <tokunaga.keiich@jp.fujitsu.com>
Cc: James Bottomley <James.Bottomley@suse.de>
Cc: Tomohiro Kusumi <kusumi.tomohiro@jp.fujitsu.com>
Cc: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/trace/trace_events.c | 208 +++++++++++++++++++++++++++++--------------
1 files changed, 141 insertions(+), 67 deletions(-)
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 53cffc0..45a8968 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -29,6 +29,8 @@ DEFINE_MUTEX(event_mutex);

LIST_HEAD(ftrace_events);

+#define COMMON_FIELD_COUNT 5
+
struct list_head *
trace_get_fields(struct ftrace_event_call *event_call)
{
@@ -544,85 +546,155 @@ out:
return ret;
}

-static ssize_t
-event_format_read(struct file *filp, char __user *ubuf, size_t cnt,
- loff_t *ppos)
+enum {
+ FORMAT_HEADER = 1,
+ FORMAT_PRINTFMT = 2,
+};
+
+static void *f_next(struct seq_file *m, void *v, loff_t *pos)
{
- struct ftrace_event_call *call = filp->private_data;
+ struct ftrace_event_call *call = m->private;
struct ftrace_event_field *field;
struct list_head *head;
- struct trace_seq *s;
- int common_field_count = 5;
- char *buf;
- int r = 0;
-
- if (*ppos)
- return 0;
+ loff_t index = *pos;

- s = kmalloc(sizeof(*s), GFP_KERNEL);
- if (!s)
- return -ENOMEM;
+ (*pos)++;

- trace_seq_init(s);
+ head = trace_get_fields(call);

- trace_seq_printf(s, "name: %s\n", call->name);
- trace_seq_printf(s, "ID: %d\n", call->event.type);
- trace_seq_printf(s, "format:\n");
+ switch ((unsigned long)v) {
+ case FORMAT_HEADER:

- head = trace_get_fields(call);
- list_for_each_entry_reverse(field, head, link) {
- /*
- * Smartly shows the array type(except dynamic array).
- * Normal:
- * field:TYPE VAR
- * If TYPE := TYPE[LEN], it is shown:
- * field:TYPE VAR[LEN]
- */
- const char *array_descriptor = strchr(field->type, '[');
-
- if (!strncmp(field->type, "__data_loc", 10))
- array_descriptor = NULL;
-
- if (!array_descriptor) {
- r = trace_seq_printf(s, "\tfield:%s %s;\toffset:%u;"
- "\tsize:%u;\tsigned:%d;\n",
- field->type, field->name, field->offset,
- field->size, !!field->is_signed);
- } else {
- r = trace_seq_printf(s, "\tfield:%.*s %s%s;\toffset:%u;"
- "\tsize:%u;\tsigned:%d;\n",
- (int)(array_descriptor - field->type),
- field->type, field->name,
- array_descriptor, field->offset,
- field->size, !!field->is_signed);
- }
+ if (unlikely(list_empty(head)))
+ return NULL;

- if (--common_field_count == 0)
- r = trace_seq_printf(s, "\n");
+ field = list_entry(head->prev, struct ftrace_event_field, link);
+ return field;

- if (!r)
- break;
+ case FORMAT_PRINTFMT:
+ /* all done */
+ return NULL;
}

- if (r)
- r = trace_seq_printf(s, "\nprint fmt: %s\n",
- call->print_fmt);
+ /*
+ * To separate common fields from event fields, the
+ * LSB is set on the first event field. Clear it in case.
+ */
+ v = (void *)((unsigned long)v & ~1L);

- if (!r) {
- /*
- * ug! The format output is bigger than a PAGE!!
- */
- buf = "FORMAT TOO BIG\n";
- r = simple_read_from_buffer(ubuf, cnt, ppos,
- buf, strlen(buf));
- goto out;
+ field = v;
+ if (field->link.prev == head)
+ return (void *)FORMAT_PRINTFMT;
+
+ field = list_entry(field->link.prev, struct ftrace_event_field, link);
+
+ /* Set the LSB to notify f_show to print an extra newline */
+ if (index == COMMON_FIELD_COUNT)
+ field = (struct ftrace_event_field *)
+ ((unsigned long)field | 1);
+
+ return field;
+}
+
+static void *f_start(struct seq_file *m, loff_t *pos)
+{
+ loff_t l = 0;
+ void *p;
+
+ /* Start by showing the header */
+ if (!*pos)
+ return (void *)FORMAT_HEADER;
+
+ p = (void *)FORMAT_HEADER;
+ do {
+ p = f_next(m, p, &l);
+ } while (p && l < *pos);
+
+ return p;
+}
+
+static int f_show(struct seq_file *m, void *v)
+{
+ struct ftrace_event_call *call = m->private;
+ struct ftrace_event_field *field;
+ const char *array_descriptor;
+
+ switch ((unsigned long)v) {
+ case FORMAT_HEADER:
+ seq_printf(m, "name: %s\n", call->name);
+ seq_printf(m, "ID: %d\n", call->event.type);
+ seq_printf(m, "format:\n");
+ return 0;
+
+ case FORMAT_PRINTFMT:
+ seq_printf(m, "\nprint fmt: %s\n",
+ call->print_fmt);
+ return 0;
}

- r = simple_read_from_buffer(ubuf, cnt, ppos,
- s->buffer, s->len);
- out:
- kfree(s);
- return r;
+ /*
+ * To separate common fields from event fields, the
+ * LSB is set on the first event field. Clear it and
+ * print a newline if it is set.
+ */
+ if ((unsigned long)v & 1) {
+ seq_putc(m, '\n');
+ v = (void *)((unsigned long)v & ~1L);
+ }
+
+ field = v;
+
+ /*
+ * Smartly shows the array type(except dynamic array).
+ * Normal:
+ * field:TYPE VAR
+ * If TYPE := TYPE[LEN], it is shown:
+ * field:TYPE VAR[LEN]
+ */
+ array_descriptor = strchr(field->type, '[');
+
+ if (!strncmp(field->type, "__data_loc", 10))
+ array_descriptor = NULL;
+
+ if (!array_descriptor)
+ seq_printf(m, "\tfield:%s %s;\toffset:%u;\tsize:%u;\tsigned:%d;\n",
+ field->type, field->name, field->offset,
+ field->size, !!field->is_signed);
+ else
+ seq_printf(m, "\tfield:%.*s %s%s;\toffset:%u;\tsize:%u;\tsigned:%d;\n",
+ (int)(array_descriptor - field->type),
+ field->type, field->name,
+ array_descriptor, field->offset,
+ field->size, !!field->is_signed);
+
+ return 0;
+}
+
+static void f_stop(struct seq_file *m, void *p)
+{
+}
+
+static const struct seq_operations trace_format_seq_ops = {
+ .start = f_start,
+ .next = f_next,
+ .stop = f_stop,
+ .show = f_show,
+};
+
+static int trace_format_open(struct inode *inode, struct file *file)
+{
+ struct ftrace_event_call *call = inode->i_private;
+ struct seq_file *m;
+ int ret;
+
+ ret = seq_open(file, &trace_format_seq_ops);
+ if (ret < 0)
+ return ret;
+
+ m = file->private_data;
+ m->private = call;
+
+ return 0;
}

static ssize_t
@@ -820,8 +892,10 @@ static const struct file_operations ftrace_enable_fops = {
};

static const struct file_operations ftrace_event_format_fops = {
- .open = tracing_open_generic,
- .read = event_format_read,
+ .open = trace_format_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
};

static const struct file_operations ftrace_event_id_fops = {
--
1.7.1



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