On Mon, 26 Jan 2015 21:40:20 +0000
Al Viro <v...@zeniv.linux.org.uk> wrote:
> Is the following correct?
> * only one directory in the entire tree (/instances) allows mkdir/rmdir.
yes
> * ftrace_trace_arrays always starts with global_trace and the rest
> is in 1-to-1 correspondence with subdirectories of /instances.
pretty much.
> * tr->name is NULL for global_trace and non-NULL for everything
> else.
yes.
> * all modifications of that list are happening from mkdir/rmdir
yes.
> * in the end of ->mkdir tr->dir set to the dentry of our subdirectory,
> and it's non-NULL (or trace_array creation simply fails)
yes.
> * global_array.dir is set to magical value ((struct dentry *)1) upon
This is new for this patch series. Currently, global_array.dir points
to the dentry of /sys/kernel/debug/tracing.
> the first call of tracing_init_dentry(). Prior to that it's NULL. BTW, may
> I politely inquire what the fuck are those contortions in
> tracing_init_dentry_tr() about? Looks like a stunningly convoluted way
> to trigger that automount point creation early in tracer_init_tracefs().
> Why not do that right there explicitly?
Yeah, that could be cleaned up. Before the tracefs code, it made much
more sense to keep that as a single function. Now that global_array.dir
is treated differently as the subdirs, it does make sense to have
global_arry.dir initialized in a separate function.
I'll update my patch series to do this.
>
> What are mount options doing? I mean, sure, you set the mode/uid/gid
> of root. Which is not modifiable anyway... And AFAICS that's all those
> options are affecting.
You mean in tracefs.c/inode.c? I have no idea, they are there from
debugfs cut and paste ;-)
>
> AFAICS, nothing ever removes files in debugfs root. Right? If so, you don't
I'm not sure about that. Well, not from tracing or from userspace. But
I believe things can be removed from debugfs root with module unload.
But are you talking about tracefs root?
> need the games with simple_pin_fs() - they are pointless in such situation
> anyway. Just do tracefs_mount = kern_mount(&trace_fs_type); in tracefs_init()
> and be done with that; lose the tracefs_mount_count and all calls of
> simple_{pin,release}_fs().
OK, cool. Because I had no idea what hey were used for anyway. ;-)
>
> While we are at it, what the hell is tracefs_file_operations about? Looks
> like some bastard offspring of /dev/null, but I don't see anything that would
> use it...
Hehe, again, this is what debugfs did and I just brought it over
thinking I needed it.
Thanks,
-- Steve
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