tracing/events: Convert format output to seq_file

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>

1 files changed, 141 insertions, 67 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 53cffc0b0801..45a8968707aa 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 = {