Messages in this thread | | | Date | Wed, 30 Sep 2009 10:20:49 -0400 | From | Theodore Tso <> | Subject | Re: [PATCH] ext4: Add a stub for mpage_da_data in the trace header |
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On Wed, Sep 30, 2009 at 09:33:35AM -0400, Christoph Hellwig wrote: > On Tue, Sep 29, 2009 at 02:40:07PM -0700, Josh Stone wrote: > > The tracepoint ext4_da_write_pages has a struct mpage_da_data* > > parameter, but that struct is only defined in fs/ext4/ext4.h. This > > patch adds a forward declaration for that struct, so this tracepoint > > header can still be used by tools like SystemTap. > > That's not what the tracepoints are for anyway. No hacks for out of > tree crap like this please - just use the trace buffer directly like > ftrace and then you don't actually need any data types. >
Josh, you do realize that SystemTap can pull stuff out of the trace buffer by examining information found in
/sys/kernel/debug/tracing/events/*/*/format
right? For example:
name: ext4_sync_fs ID: 600 format: field:unsigned short common_type; offset:0; size:2; field:unsigned char common_flags; offset:2; size:1; field:unsigned char common_preempt_count; offset:3; size:1; field:int common_pid; offset:4; size:4; field:int common_tgid; offset:8; size:4;
field:dev_t dev; offset:12; size:4; field:int wait; offset:16; size:4;
print fmt: "dev %s wait %d", jbd2_dev_to_name(REC->dev), REC->wait
No need to for users to download gigabytes and gigabytes of DWARF crapola (and for developers to grow old waiting for a kernel compile with -g enabled to complete); SystemTap can just get what it needs straight out of /sys/kernel/debug/tracing/events, and then reading what it needs out of the ring buffer.
In any case I've added the blind structure pointer to include/trace/events/ext4.h, but in the long term you're *much* better off pulling the information you need from the ftrace ring buffer and getting the information you need to interpret it out of /sys/kernel/debug/tracing.
- Ted
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