Re: [PATCH] blk queue io tracing support

[Jens Axboe <axboe@suse.de>]

On Wed, Aug 31 2005, Nathan Scott wrote:
> Hi Jens,
> 
> On Wed, Aug 24, 2005 at 11:28:39AM +0200, Jens Axboe wrote:
> > Ok, updated version.
> 
> One thing I found a bit awkward was the way its putting all inodes
> in the root of the relayfs namespace, with the cpuid tacked on the
> end of the bdevname - I was a bit confused at first when a trace of
> sdd on my 4P box spontaneously created files for "partitions" sdd0,
> sdd1, sdd2, and sdd3 ;).
> 
> I suppose if many more users of relayfs spring into existance, this
> is going to get quite ugly.  Below is a patch that aligns the names
> to the conventions used in sysfs; so, for example, when running two
> traces simultaneously on /dev/sdd and /dev/sdb, instead of this:
> 
> # find /relay
> /relay
> /relay/sdd3
> /relay/sdd2
> /relay/sdd1
> /relay/sdd0
> /relay/sdb3
> /relay/sdb2
> /relay/sdb1
> /relay/sdb0
> 
> it now uses this...
> 
> # find /relay
> /relay
> /relay/block
> /relay/block/sdd
> /relay/block/sdd/trace3
> /relay/block/sdd/trace2
> /relay/block/sdd/trace1
> /relay/block/sdd/trace0
> /relay/block/sdb
> /relay/block/sdb/trace3
> /relay/block/sdb/trace2
> /relay/block/sdb/trace1
> /relay/block/sdb/trace0
> 
> and does the correct dynamic setup and teardown of the hierarchy
> as the userspace tool starts and stops tracing.  I had to modify
> the relayfs rmdir code a bit to make this work properly, I'll
> send a separate patch for that shortly.
> 
> > http://www.kernel.org/pub/linux/kernel/people/axboe/tools/blktrace.c
> > 
> > has been updated as well, the protocol version was increased to
> > accomodate the trace structure changes.
> 
> I have the associated userspace change for this, as well as several
> other fixes and tweaks for your tool - if you could slap a copyright
> and license notice onto that source (pretty please? :) I'll send 'em
> right along.

I've committed this patch. However, there's an issue with it:


> +static struct dentry *blk_create_tree(const char *blk_name)
> +{
> +	struct dentry *dir;
> +
> +	spin_lock(&blk_tree_lock);
> +	if (!blk_tree_root) {
> +		blk_tree_root = relayfs_create_dir("block", NULL);
> +		if (!blk_tree_root) {
> +			spin_unlock(&blk_tree_lock);
> +			return NULL;
> +		}
> +	}
> +	dir = relayfs_create_dir(blk_name, blk_tree_root);
> +	if (!dir)
> +		blk_remove_root();
> +	spin_unlock(&blk_tree_lock);

That doesn't look very safe, relayfs_create_dir() could block. I've
changed the blk_tree_lock to be a simple mutex instead. The patch is
committed to the git repo.

-- 
Jens Axboe